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THE
ACTION OF LIGHTNING
THE MEANS OF DEFENDING LIFE AND
PROPERTY FROM ITS EFFECTS
BY
AKTHUB PAENELL
MAJOR IN THE CORPS OF ROYAL ENGINEERS
i/TT '
1 U '
LONDON
CROSBY LOCKWOOD AND CO.
7, STATIONEES' HALL COURT, LUDGATE HILL
1882
FSIWTBD BY J. S. VIRTUE AND CO., LIM7TBD,
CITT BOAD.
PREFACE.
THE object of this work is to present in some detail the
probable nature of the action of lightning, and to suggest
means which shall tend to give better and more economical
defence to life and property against its effects than is
afforded by the methods now in use.
The work is divided into three Pari;s.
Part I. consists of recorded facts and opinions. The
latter have been compiled partly as supplying evidence of
the ideas generally entertained on the subject, and partly
for the purpose of fortifying the views now advanced.
Part II. is a superstructure of theory erected on the
foundation of fact and electrical law comprised in the fore-
going Part.
Part III. is the practical outcome of this theory, and
describes the various defensive measures advocated.
DEVONPORT,
April 30^, 1881.
TABLE OF CONTENTS,
LIST OF AUTHORITIES.
PART I. FACTS AND OPINIONS.
CHAPTER I. NOTES ON LIGHTNING.
PAGE
SECTION A. ELECTRICAL NOTES . . . . 1
(a) Electricity 1
(b) Electrical Measurement . . . . ... 2
(e) Potential 3
(d) Insulation 4
(e) Induction . . . 4
(/) Condensation 5
(g] Electric Sparks 6
SECTION B. THE CONDUCTIVITY OF MATERIALS . ... 6
SECTION C. THE ELECTRICITY AND MAGNETISM OF THE EARTH 10
(a) Atmospheric Electricity 10
(b) Rain and Hail ; . . 12
(c) Clouds . 13
(d) Terrestrial Electricity 14
(e) Earth Currents 16
(/) The Earth's Magnetism 17
(g) Aurorso 20
(*) St. Elmo's Fires . . . . - . . . .21
(i) Waterspouts 22
<*) Earthquakes 23
(I) Volcanic Eruptions 25
VI TABLE OF CONTENTS.
PAGE
SECTION D. LIGHTNING DISCHARGES 26
(*) The Nature of Lightning 26
(b) The Action of Lightning on Materials . . . .30
(e) Return Strokes 31
(d) The Effect of Lightning on Persons . . .32
(e) The Effect of Lightning on Telegraphs .... 33
SECTION E. THE INFLUENCE OF METALS ON LIGHTNING . . 35
SECTION F. PRESERVATIVES FROM LIGHTNING . . . .36
SECTION G. STATISTICAL AND GEOGRAPHICAL NOTES . . .39
CHAPTER II.- NOTES ON LIGHTNING ENGINEERING.
SECTION A. HISTORICAL NOTES 47
SECTION B. DETAILS OF LIGHTNING RODS 52
SECTION C. POINTS OF RODS .59
SECTION D. EARTH CONNECTIONS OF RODS 65
SECTION E. THE APPLICATION OF RODS 70
SECTION F. THE INSPECTION OF RODS 75
SECTION G. THB PROTECTIVE POWERS OF RODS . . .77
CHAPTER III. SOME INCIDENTS OF LIGHTNING
ACTION.
CHAPTER IV. SOME INSTANCES OF EXISTING LIGHT-
NING RODS.
PART II. THE THEORY OF THE ACTION OF
LIGHTNING.
CHAPTER V. ELECTRICAL DEFINITIONS AND DATA.
SECTION A. ELECTRICAL DEFINITIONS 145
(a) Fundamental Terms 145
(b) The Influence of Bodits 147
(c) The Nature of Condensers 147
TABLE OF CONTENTS. Vll
PAGE
SECTION B. ELECTRICAL DATA 148
(a) Electrical Formulae 148
(b) The Three Elements of Electricity 149
(c) Collectors and Insulators 150
(d) Electrical Explosions 150
(e) Electrical Keturn Strokes 151
(/) Electrical Leaks 151
(g] Illustrations of Electrical Action 152
CHAPTER VI. THE CONSTITUTION OF THE TERRES-
TRIAL CONDENSER.
SECTION A. THE FUNCTION OF THE EARTH IN THE TERRESTRIAL
CONDENSER 154
(a) The Relation between the Earth and the Clouds . .154
(b) The Earth's Electricity 156
SECTION B. THE THEORY or DESCENDING LIGHTNING . . 160
(a) Facts Regarding Descending Lightning . . . .160
(b) Descending Lightning from the Aspect of Electrical Law 165
SECTION C. THE OUTLINE OF THE TERRESTRIAL PLATE . .167
SECTION D. THE INFLUENCES OF THE MATERIALS COMPOSING
THE TERRESTRIAL CONDENSER . . . .170
(a) Table of Influences of Various Substances . . .171
(I) Remarks on the Table 174
SECTION E. THE DISCHARGE OF THE TERRESTRIAL CONDENSER 174
(a) The Various Forms of Terrestrial Electrical Discharge . 174
(b) The Rationale of Thunderbolts 176
CHAPTER VII. THE ACTION OF THUNDERBOLTS.
SECTION A. THE ELECTRICAL CONDITIONS OF THE EARTH'S
SURFACE 179
(a) The Accumulation of Electricity on the Earth's Surface 179
(b) Surfaces of Water 180
() Moist Earth . . . 182
(d) Rocky and Dry Surfaces 182
(e) Paved Surfaces 183
(/) Surfaces Formed by Railway Metals . . . .185
(ff) The Shape and Geological Formation of the Ground . 185
(h) Analysis of Incidents in regard to Conditions of Surface 186
TABLE OF CONTENTS.
PAGE
SECTION B. DETAILS OP THUNDERBOLT ACTION . . . .187
(a) Classification of Objects on the Earth's Surface . . 187
() Electrical Connection 189
(c) Explosive Action 190
(d) Local Plates . 194
(<?) Persons in the Open Air 196
(/) Local Dielectrics 198
(g) Accidental Dielectrics Formed by Local Plates . . 201
(/*) The Protection Afforded by the Interiors of Buildings . 203
(i) The Dangers to which Interiors are Liable . . . 204
(A) The Special Danger from Chimneys . . . .206
(/) Simultaneous Strokes of Lightning 209
SECTION C. ANALYSIS OF THUNDERBOLT INCIDENTS . . . 209
(1) Buildings 210
(2) Ships . . . 212
(3) Metals 213
(4) Chimneys 215
(5) Trees 215
(6) Flagstaff's, Masts, &c 216
(7) Telegraphs . . 216
(8) Persons 216
(9) Animals 218
(10) Simultaneous Strokes . . . . . . .218
(11) Repeated Strokes 219
(12) Accurately defined Strokes 219
(13) Horizontally directed portions of Strokes . . .219
(14) Acts of Mechanical Force (except to Lightning Rods) ex-
clusive of Rending of Masonry 219
(15) Objects which, when Struck, probably formed Local
Plates . 219
(16) Objects which, when Struck, probably formed Local
Plates, associated with Local Dielectrics . . . 220
(17) Objects which, when Struck, probably formed Local
Plates, accidentally constituting Local Dielectrics . 220
(18) Objects which, when Struck, probably formed Local
Dielectrics . . . .220
SECTION D. ATMOSPHERIC DIELECTRICAL CONDITIONS . . 220
(a) The Influence of Rainfall 221
(&) The Temperature of the Air 222
(c) Atmospheric Electricity 223
TABLE OF CONTENTS. IX
PAGE
SECTION E. CLOUDS AND CLOUD EXPLOSIONS . . . . 223
(a) The Electrical Conditions of the Clouds . . . .223
(b) The Electricity Due to the Conversion of the Clouds into
Rain 224
(c) Cloud Explosions 225
(d) Thunderstorms 226
SECTION F. TERRESTRIAL RETURN STROKES .... 227
(a) Nature of Terrestrial Return Strokes .... 227
(b) Return Strokes Induced by Cloud Explosions . . . 228
(c) Return Strokes Induced by Thunderbolts . . .229
(d) The Effect of Return Strokes on Telegraphs . . ,230
SECTION G. TERRESTRIAL LEAKS 231
(a) Atmospheric Porous Leaks 231
(b) Terrestrial Angular Leaks 232
(c) The Value of Metal Points in Relation to the Earth . 233
(d) Terrestrial Valves afforded by Features of Civilisation . 235
(<?) The Angular Leakage of Metals 236
CHAPTER VIII.THE PRESENT SYSTEM OF LIGHT-
NING RODS.
SECTION A. OBSERVATIONS ON THE HISTORY OF LIGHTNING
RODS 238
(a) The Invention of Lightning Rods 238
(b) Theory of the Functions of Rods 238
(c) The Opposition to the Use of Rods 242
(d) Diverse Systems of Application 244
SECTION B. COMMENTS ON THE THEORY AND PRACTICE OF
LIGHTNING ROD DEFENCE .... 245
(a) The Exposure of Elevated Metal ..... 246
(b) The Costliness of Rods 249
(c) The Sources of Failure to which Rods are Liable . . 254
(d) The Tendency of Rods to Disfigure Buildings . . .257
SECTION C. ANALYSIS OF LIGHTNING INCIDENTS CONNECTED
WITH RODS , 258
(1) Rods Struck 258
(2) Constructions Struck, but not the Rods .... 259
(3) Constructions, without Rods, Damaged, Close to Other
Constructions which had Rods, but Received no
Damage 259
X TABLE OF CONTENTS.
PAGE
(4) Buildings Struck before being Supplied with Rods, but
not Subsequently 259
(5) Causes to which the Failures of Rods have been Attributed
by Authorities 259
(6) Rods which probably Acted as Local Plates . . .260
(7) Rods which probably Acted as Accidental Dielectrics . 260
(8) Rods which probably Acted as Local Dielectrics . . 260
(9) Ends of Rods Fused 260
(10) Mechanical Injuries to Rods 260
(11) Deviations of the Explosions from the Rods . . .261
(12) Notes 261
SECTION D. SUMMARY OF REMARKS ON LIGHTNING RODS . . 264
PART III. PRACTICAL MEASURES ADVOCATED
FOR THE DEFENCE OF LIFE AND PRO-
PERTY FROM THE EFFECTS OF LIGHT-
NING.
CHAPTER IX. PRACTICAL MEASURES ADVOCATED.
SECTION A. THE DEFENCE OF LARGE AREAS .... 267
(a) The Defence of Countries and Districts .... 267
(b) The Defence of Towns 269
SECTION B. THE DEFENCE OF CONSTRUCTIONS .... 270
(a} The Removal of Metal and Explosive Conditions . .271
(b) The Reduction of the Explosiveness of the Ground . . 276
(c) The Conversion of Chimney Grates into Electric Taps . 278
(d) The Application of Electric Taps to the Ground Sur-
rounding the Building 280
(c) Summary of Proposals for the Defence of Buildings . 285
(/) The Defence of Coal Mines . . . . .287
(g) The Defence of Ships 288
SECTION C. THE DEFENCE OF INDIVIDUALS .... 289
(a) Rules for the Guidance of Individuals . . . .289
(b} Agricultural Labourers 291
TABLE OP CONTENTS. XI
LIST OF AUTHOKITIES.
Most of the notes and incidents in Chapters I., II., and III. have
been extracted from the following authorities, which are respectively
denoted by the accompanying abbreviations :
(1.) " Encyclopsedia Britannica." Edition 1857 . . Enc. Br.
(2.) "The Life of Benjamin Franklin, written by Himself."
Edited by John Bigelow. London: Lippincott. 1879. frank,
(3.) " Aide-Memoire to the Military Sciences, framed from
Contributions of Officers of the different Services, and
edited by a Committee of the Corps of Royal Engineers."
London : John Weale. 1853. Article on " Geognosy,"
by Colonel J. E. Portlock, B.E., F.R.S. . . Portl. A. M.
Article on "Electricity," by Colonel R. J. Nelson, R.E.
Nets. A. M.
(4.) Franqois Arago's " Meteorological Essays," translated by
Colonel Sabine, R.A., F.R.S. London: Longmans. 1855. Ar.
(5.) "Papers on Subjects Connected with the Duties of the
Corps of Royal Engineers." Vol. XVIII. Article by Lieut.
T. Fraser, R.E., " How Earthquakes can be Observed and
Registered." Fras. R. E. JP.
(6.) "Aide-Memoire for the use of Officers of Royal Engineers."
Compiled by Colonel A. C. Cooke, C.B., R.E. Vol. 1.
London. 1879 E. E. A.
(7.) "Library of Useful Knowledge. Natural Philosophy."
Vol. II. "Electricity," by Dr. Roget. London: Bald-
win . t Roy.
(8.) "Elementary Treatise on Physics, Experimental and
Applied." Translated and edited from " Ganot's Elements
de Physique," by E. Atkinson, Ph.D., F.C.S., Professor of
Experimental Science, R.M.C., Sandhurst. Third Edition.
London: Longmans. 1868 Gan.
(9.) " The Medical Remembrancer, or Book of Emergencies,"
by Edward B. L. Shaw. Fourth Edition. London:
Churchill. 1856 Shaw.
(10.) Journal of the Society of Telegraph Engineers for 1872.
S. T. E.
(11.) Herschel's Meteorology. A. and C. Black. 1862.. Hersch.
(12.) Kaemtz's Meteorology. Translated by C. V. Walker.
1845 Kaetn.
(13.) "Electricity and Magnetism," by Fleeming Jenkin,
F.R.S.S., L. and E., M.I.C.E., Professor of Engineering
Xll TABLE OF CONTENTS.
in the University of Edinburgh. London: Longmans.
1873 Jen.
(14.) Culley's "Lectures on Construction and Maintenance of
Telegraph Lines," delivered at the S.M.E., Chatham.
February, 1869 Cull.
(15.) "The Atmosphere," by Camille Flammarion. Translated
from the French, and edited by James Glaisher, F.R.S.
London. 1873 Flam.
(16.) "On the Nature of Thunderstorms, and on the means of
Protecting Buildings and Shipping against the Destructive
Effects of Lightning," by W. Snow Harris, F.R.S. London :
Parker. 1843. . . . . . . Harr.
(17.) " Lessons in Electricity," delivered at the Royal Institu-
tion in 1875-6, by John Tyndall, Professor of Natural
Philosophy, Royal Institution of Great Britain. London :
Longmans. 1876 Tynd.
(18.) "On the Protection of Buildings from Lightning," by
R. J. Mann, M.D. A paper read at a meeting of the
Society of Arts, 28th April, 1875, and published in their
Journal. Letter from Dr. Mann to the Times, 23rd
November, 1877. "Further Remarks concerning the Light-
ning Rod," by Dr. Mann. A paper read at a meeting of
the Society of Arts, 15th March, 1878, and published in
their Journal. Mann.
(19.) Chambers's" English Dictionary." 1877. . . Chamb.
(20.) "On Lightning and Lightning Conductors," by W. H.
Preece, M.I.C.E. A paper read at a meeting of the Society
of Telegraph Engineers, on the 27th November, 1872, and
published in their Journal. Also other papers by the same
author Preece.
(21.) Inaugural address to the Society of Telegraph Engineers,
on the 15th January, 1874, by Sir William Thomson,
F.R.S., LL.D. (also other quotations from the same
author). Thorns.
(22.) Registrar-General's Report for England and Wales 1877-
1878 Beg. Engl
(23.) Registrar-General's Report for Ireland, 1877-1878. Reg. Irel.
(24.) W*r Office Instructions as to >.
f u~v,*^ -} / 24th July, 1829,
che application of lightning
18th March, 1846,
conductors for the protection V ' } W. 0.
^
of powder magazines andj ( 6th A 1875 .
other buildings. '
[NOTE. The appendixes A and B to W.O. Instructions of 25th of May, 1858, are
by Sir W. Snow Harris.]
TABLE OF CONTENTS. XI 11
(25.) "Rough Notes on Electricity." Chatham. 1873 . Chath.
(26.) "Lightning Conductors, their History, Nature, and Mode
of Application," by Richard Anderson, F.C.S., F.G.S.,
Member of the Society of Telegraph Engineers. London :
Spon. 1879 And.
(27.) " Encyclopaedia of Experimental Philosophy." "Electri-
city," by the Rev. Francis Lunn, A.M., F.R.S. . Lunn.
(28.) Clark and Sabine's Electrical Tables and Formulae . Clark.
(29.) Desohanel's "Natural Philosophy," edited by Professor
Everett, F.R.S. 1872 Desch.
(30.) "How to Build a House," a translation by B. Bucknall,
Architect, of Viollet-le-Duc's ' Histoire d'une Maison."
London : Sampson Low & Co. 1874 . . . Violl.
(31.) Buchan' s "Handy Book of Meteorology." Second Edition.
Edinburgh: Blackwood. 1868 . . . . Such.
(32.) " Scrambles amongst the Alps in the Years 1860-69," by
Edward Whymper. London: Murray. 1871. . Whymp.
(33.) Report of Major Majendie, R.A., H.M. Inspector of Ex-
plosives, to the Home Secretary, dated 17th September,
1878 Rep. Expl.
(34.) Royal Engineers' Journal, 1876.; No. Ixiii. . . R.E.J.
(35.) The Wellington Weekly Gazette W.W.G.
(36.) The Telegraphic Journal and Electrical Review . . . Tel.
(37.) Symons' Meteorological Magazine . . . S.M.M.
(38.) The Times newspaper . . . . * . . Times.
(39.) The Illustrated London News I.L.tf.
(40.) The Standard newspaper Stand.
(41.) The Graphic newspaper Graph.
(42.) The Western Morning News W.M.N.
(43.) The Western Weekly News W.W.N.
(44.) Kentish newspaper K.P.
(45.) Mr. Von Fischer Treuenfeld, M.S.T.E. . . . Trett.
(46.) M. Francisque Michel franc. Mich.
(47.) Mr. G. J. Symons, F.R.S Sym.
(48.) Mr. Latimer Clark, F.R.S Lat. Clark.
(49.) Mr. James Graves, M.S.T.E. .... Grav.
(50.) M. E. Nouel Nouel.
(51.) Captain D. Galton, F.R.S., C.B Gait.
(52.) Professor Abel, F.R.S Abel.
(53 ) Mr. W. E. Ayrton, M.S.T.E Ayrt.
(54.) " A Physical Treatise on Electricity and Magnetism," by
J. E. H. Gordon, B.A. Camb., Assistant Secretary of the
British Association. London : Sampson Low & Co.
1880. . Gord.
I. A a 1-4
ON LIGHTNING.
fart S.
FACTS AND OPINIONS.
CHAPTEE I. NOTES ON LIGHTNING.
(A.) ELECTRICAL NOTES.
(a) Electricity.
(1.) ELECTRICITY is one form of energy, and therefore
necessarily force, and not matter. (Preece, 337.)
(2.) " Electricity is a powerful physical agent which
manifests itself mainly by attractions and repulsions,
but also by luminous and heating effects, by violent
commotions, and many other phenomena." (Gan. 584.)
(3.) "It may be impossible that we shall ever arrive at
a perfect knowledge of the subtle operations from whence
the phenomena of electricity result. Therefore any theo-
retical view of them, as of many other questions in
physical science, is but a sort of intellectual contrivance
for representing to the mind the order and connection sub-
sisting between observed phenomena." (Harr. 66.)
(3a.) " We have as yet no conception of electricity apart
from the electrified body; we have no experience of its
independent existence." (Gord. i. 1.)
(4.) The science of electricity "has two great divisions ;
the one called 'Frictional electricity,' the other 'Voltaic
electricity.' " (Tynd. 19.)
2 LIGHTNING.
I. A I 58.
(5.) Electricity is derived from the following sources,
viz. :
1. Friction.
2. Induction.
3. The contact of dissimilar metals.
4. The contact of metals with liquids.
5. " A mere variation of the character of the contact of two bodies."
6. " Chemical action produces a continuous flow of electricity
(roltaic electricity)."
7. "Heat, suitably applied to dissimilar metals, produces a con-
tinuous flow of electricity (thermo-electricity)."
8. The heating and cooling of certain crystals (pyro-electricity)."
9. " The motion of magnets and of bodies carrying electric currents
(magneto-electricity) ."
10. " The friction of sand against a metal plate."
11. "The friction of condenged water particles against a safety
valve, or, better still, against a boxwood muzzle, through which
steam is driven (Armstrong's hydro-electric machine)." (Tynd. 110.)
(b) Electrical Measurement.
(6.) In electro-static measurement, it is found by experi-
ment that when F is the force of repulsion or attraction
between two small electrified bodies, Q and Q^ the
charges or quantities in those bodies, and D their dis-
tance apart, then
F = -j^ 1 , and, where Qj = Q, F ^ 2 ,
whence the value of Q, can be determined. (Jen. 95.)
(7.) If Q is the quantity of electricity on a body,
S ,, ,, capacity of such body, and
P ,, potential
then Q = PS. (Jen. 96 & 97.)
(8.) " The following table of dimensions and constants
is taken from the British Association Report on Electrical
Standards, 1863."
" Fundamental units
Length = L.
Time = T.
Mass = M."
NOTES ON LIGHTNING. 3
I. A c 912.
Derived mechanical units
Force = F = ^ L .
Velocity =V==."
" Electrostatic system of units
Quantity of electricity = Q = _1.
T .
Strength of electric current = =
Electro-motive force = E = ..
m
Eesistance of conductor =. R =_."
L
(Jen. 163 & 164.)
(9.) Distance = 1. Mass = m. Time = t. Velocity =
7 7
T . Acceleration = - = _. Force = acceleration x mass
t t t*
= ~. Work = force X distance = ~. (Desch.)
t t
(10.) Quantity = fll = ^LL*. Potential = work
t quantity
= ^. Capacity = ^ntity
t potential
(11.) Ohm's law.
n Electro-motive force / T Q0 N
Laurent = =r ; . (Jen. 82.)
Resistance
(0) Potential.
(12.) Potential may be compared with a head of water.
07^. 10 & 40.)
B2
4 LIGHTNING.
I. A de 1320.
(13.) " Difference of potential is a difference of electrical
condition in virtue of which work is done by positive
electricity in moving from the point at a higher potential
to that at a lower." (Jen. 26.)
(d) Insulation.
(14.) An insulated surface can only lose its electricity
gradually. (Jen. 3.)
(15.) " We may expect that if from any cause the distribu-
tion of electricity in a body can be varied, even without its
total amount being changed, this redistribution will take
place almost instantaneously in the electrified conductor,
and much more slowly in the electrified insulator."
(Jen. 3.)
(16.) " No substance is found to insulate so perfectly as
to possess the power of keeping the two electricities
asunder for more than a limited time. A perpetual leak-
age is always occurring from the one to the other through
the mass of the insulator, until the combination or neutral-
isation is complete, and all signs of electricity disappear."
(Jen. 8.)
(e) Induction.
(17.) If a positively charged body A be brought
near an uncharged body B, "it attracts negative elec-
tricity to that end of the body B which is near it, and
repels positive electricity to the remoter portions of B."
(Jen. 11.)
(18.) "Induction of electricity must take place in the
space surrounding every electrified body." (Jen. 12.)
(19.) "Induction always takes place between two con-
ductors at different potentials separated by an insulator."
(Jen. 13.)
{20.) " The very existence of the original charge im-
plies the induced charge." (Jen. 13.)
NOTES ON LIGHTNING. 5
I. A/ 20a 26.
(200.) " The only manner in which we can in any way
account for the observed facts of attraction, repulsion, and
induction is by assuming that the forces are transmitted
by a strain or distortion of the medium which fills the
space between the electrified bodies." (Gord. i. 20.)
(/) Condensation.
(21.) " Whenever a conductor is charged, a kind of
Leyden jar is necessarily formed. The conductor is the
inner coating, the air the dielectric, and the nearest sur-
rounding conductors . . . form the outer coating." (Jen.
19.)
(22.) "A condenser is an apparatus for condensing a
large quantity of electricity on a comparatively small sur-
face. The form may vary considerably, but in all cases
consists essentially of two insulated conductors, separated
by a non-conductor, and depends on the action of induc-
tion." (Gan. 622.)
(23.) Condensation is the " operation of obtaining elec-
tricity of high potential from a source of comparatively
low potential." (Chath. 134.)
(24.) Franklin found that the electricity in a condenser
resides in the dielectric. This can be proved by making
the coatings of a Leyden jar movable. (Tynd. 78.)
(25.) "The coefficient by which the capacity of an air
condenser must be multiplied in order to give the capacity
of the same condenser when another dielectric is sub-
stituted for air is constant for each substance, and is
called the ' specific inductive capacity' of the dielectric."
(Jen. 97.)
(25#.) Specific inductive capacity is " the specific power
of the substance of which the insulator is composed of
receiving and transmitting that electric strain which we
call induction." (Gord. i. 69.)
(26.) Approximate specific inductive capacities :
6 LIGHTNING.
I. A ^27 31; Bl, 2.
Air 1
Pitch 1-8
Glass . .1-9
India-rubber. . . . 2*8
Gutta-percha. . . .4*2
Mica 5
(Jen. 96.)
(g) Electric Sparks.
(27.) Electric sparks are said to overcome the resistance
of the air, but this resistance has nothing in common with
the resistance which is the subject of Ohm's law." (Jen.
92.)
(28.) Sir Charles Wheatstone found in a special case the
duration of an electric spark to be TT&tro of a second, but
this was the maximum. In other cases it was less than
nn>fcoTT<r of a second. (Tynd. 85.)
(29.) " The recombination of the two electricities which
constitute the electrical discharge may be either continu-
ous or sudden ; . . . . sudden, as when the opposite elec-
tricities accumulate on the surface of two adjacent con-
ductors, till their mutual attraction is strong enough to
overcome the intervening resistances, whatever they may
be." (Gan. 638.)
(30.) " The brush forms when the electricity leaves the
conductor in a continuous flow, the spark when the dis-
charge is discontinuous." (Gan. 639.)
(31.) " When an electric discharge is sent through gun-
powder placed on the table of a Henley's discharger, it is
not ignited, but is projected in all directions." ( Gan. 643.)
(B.) THE CONDUCTIVITY OF MATERIALS.
(1.) Cavendish estimated iron to be 400,000,000 times
more conductive than water. (Harr. 7.)
(2.) Relative conductivity of building metals (according
to Sir Win. Snow Harris) :
Lead 1
Tin 2
Iron 2
Zinc 4
Copper 12
(W. 0. 1875, 36.)
NOTES ON LIGHTNING. 7
I. B 36.
(3.) Extracts from table of conductivity given by Sir
W. S. Harris:
Most
Perfect.
" Condttcton."
( Metals.
I Charcoal.
( Plumbago.
Flame.
I Smoke.
( Living animals.
Perfect." \ Living vegetables.
Wood.
Snow and Ice.
Aqueous vapour.
Common earth and
stone.
Dry chalk and
lime.
Marble and porce-
lain.
v Paper.
Less
Perfect."
" Imperfect."
"Most
Perfect."
' Insulator t."
Ice at 0.
Dried vegetable sub-
stances.
Dried animal sub-
stances.
Parchment, leather,
feathers.
Bituminous matter.
Silk.
Animal fur and hair.
Dry gases, including
atmosphere.
Pure steam of high
elasticity.
Glass and all vitre-
f actions.
All resins and resinous
bodies.
(Earr. 7.)
(3.) Matthiesen gives graphite and gas-coke as 1,450
to 40,000 times less conductive than pure copper. (Jen.
257.)
(4.) Earefied gases are found to be tolerably good con-
ductors. (Jen. 93.)
(5.) The conductivity of silver to that of gutta-percha is
85 X 10 20 to I. (Jen. 85.)
(6.) Extracts from Eoget's <; Catalogue of Bodies in the
order of their Conducting Power : "
The least perfect or least oxidable
metals.
The more oxidable metals.
Charcoal prepared from the harder
woods and well burned.
Plumbago.
Metallic ores.
Animal fluids.
Pure water.
Snow.
Living vegetables.
Living animals.
Flame.
Smoke.
Steam.
Rarefied air.
Earths and stones in their ordinary
state.
Vegetable ashes.
Animal ashes.
Ice below 13 Fahrenheit.
Lime.
8
LIGHTNING,
I. B 710.
Chalk.
India-rubber.
Siliceous and argillaceous stones
in proportion to their hard-
ness.
Dry marble.
Porcelain.
Dry atmospheric air and other
gases.
Leather.
Dry paper.
Cotton.
Feathers.
Hair, especially that of a living cat.
Wool.
Dyed silk.
Bleached silk.
Baw silk.
Glass and other vitrefactiona.
Fat.
Kesins and bituminous substances.
(Rog. ii. 6.)
(7.) The deposition of moisture on an insulator increases
the conducting power. (Hog. ii. 7.)
(8.) Lunn gives practically the same order of conductivity
as Roget. The following are the principal differences,
viz. :
/ 1st. " Sea water."
a) In lieu of 2nd . Spring water>
"pure water. ) ^ R ain water."
(/3) Between "rain water" and "snow," "ice above 13 D Fahr."
is inserted,
(y) For "earths and stones in their ordinary state" "moist
earths and stones."
(i) Between "porcelain" and "air," "dry vegetable bodies" are
inserted. (Lunn t 72.)
(9.) Extracts from Tyndall's list of conductivity :
" Conductors."
The common metals.
Well-burned charcoal.
Bain water.
Linen.
Vegetables and animals.
" Semi-Conductors."
Wood.
Marble.
Straw.
" Insulators"
Chalk.
India-rubber.
Paper.
Hair.
Silk.
Glass.
(Tynd. 18.)
(10.) Conductivity of pure copper = 100,000,000. Ditto
of solution of concentrated common salt = 31-52. (Clark.}
NOTES ON LIGHTNING. 9
I. B 1114.
(11.) Extracts from list in E. E. Aide-Memoire of ' ' Bodies
arranged in the order of their relative conducting power : "
" Conductors."
"Most Perfect"
All known metals.
Well-burned charcoal.
Plumbago.
Burning gaseous matter, as flame.
Smoke.
" Less Perfect."
Dry chalk and lime.
Marble and porcelain.
Paper.
Wood in its ordinary state.
Water.
Snow and ice from 32 to 0.
Living animals.
Living vegetables.
Aqueous vapour.
Common earth and stone.
"Non-conductors or Insulators."
" Less Perfect."
Ice below of Fahrenheit.
Dried vegetable substances.
Dried animal substances.
Parchment, leather, feathers.
Fur and hair.
Silk.
Most Perfect."
Dry air and other gases.
Pure steam of high elasticity.
Glass and all vitrefactions.
All resins and resinous bodies.
(R. E. A. 56.)
(12.) Order of conductivity of metals, fro.:
Silver 100
Copper 99-9
Gold 80
Zinc 29
Platina 18
Iron 16-8
Tin 13-1
Lead 8*3
German silver . . . 7'7
Mercury 1*6
Bismuth 1*2
Graphite 0-07
(. E. A. 56.)
(13.) Those bodies are " conveniently designated as
conductors which when applied to a charged electroscope
discharge it almost instantaneously, semi-conductors being
those which discharge it in a short but measurable time a
few seconds for instance ; while non-conductors effect no
discharge in the course of a minute." (G-an. 587.)
( 14. ) The following list * ' is arranged in order of decreas-
ing conductivity, or, what is the same thing, of increased
resistance. The arrangement is not invariable, however.
Conductivity depends on many physical conditions." The
following are extracts from the list :
B 3
10
I. B 15, 16.
" Conductors."
Metals.
Well-burnt charcoal.
Graphite.
Aqueous solutions.
Water.
Snow.
Vegetables.
Animals.
Linen.
Cotton.
LIGHTNING.
Ofll 3.
" Semi-conductors."
Wood.
Ice at 0.
" Non-conductors."
Ice at 25 C.
Lime.
Caoutchouc.
Air and dry gases.
Dry paper.
Silk.
Glass.
Resins.
(Gan. 586.)
(15.) The average result of the researches of Sir
Humphrey Davy, Becquerel, Lenz, Ohm, and Pouillet as
regards the relative conductivity of copper and iron fixes
the proportion as that of 100 to 16. (And. 55.)
(16.) Specific resistances of substances in absolute units,
as given by Professor Everett, F.R.S., in his "Units and
Physical Constants : "
Silver, hard drawn
Copper
Gold
Iron, annealed
1609
1642
2154
9827
Lead, pressed .... 19,847
Water at 22 C. . . 7' 18 X 10 10
Gutta-percha at 24 C. 2-53 X 10 23
(Gord. i. 259.)
(0.) THE ELECTRICITY AND MAGNETISM OF THE EARTH.
(a) Atmospheric Electricity.
(1.) "The electric telegraph forces us to combine our
ideas with reference to terrestrial magnetism and atmo-
spheric electricity. We must look on the earth and air as
a whole a globe of earth and air and consider its elec-
tricity, whether at rest or in motion." This science is that
of " terrestrial electricity." (Thorns. Tel. 15/1/74.)
(2.) " The subject of atmospheric electricity is yet in its
infancy, and is one of extreme difficulty." (Do. S. T. E.
369.)
(3.) "No connection between atmospheric electricity,
thunderstorms, or generally the state of the weather, has
yet been discovered." (Do.}
NOTES QN LIGHTNING. 11
I. C4 14.
(4.) "There is no reason to suppose that clouds are
essential to electrical discharge in the atmosphere. On
the contrary, instances are recorded, both in ancient and
modern times, of lightning flashes occurring in a perfectly
clear sky." (Do.)
(5.) " In fair weather, the surface of the earth is always,
in these countries at all events, found negatively elec-
trified." (Do. Tel. 15/1/74.)
(6.) " Positive electricity of the air is merely inferential.
The result obtained in daily observations is precisely the
same as if the earth were electrified negatively, and the air
had no electricity in it whatever." (Do.)
(7.) " Probably all space is non-conductive, and the
upper regions of the air have no electricity." (Do.)
(8.) The atmosphere always contains free electricity,
sometimes positive, and sometimes negative. (Gfan. 827.)
(9.) The electricity of the ground is always negative;
but it varies according to the hygrometric and thermometric
states of the air. (Do. 828.)
(10.) " Many hypotheses have been propounded to ex-
plain the origin of atmospheric electricity. Some have
ascribed it to the friction of the air against the ground,
some to the vegetation of plants, or to the evaporation of
water. Some again have compared the earth to a vast
voltaic pile, and others to a thermo- electrical apparatus.
Many of these causes may in fact concur in producing the
phenomena." (Do.)
(11.) Yolta showed that evaporation produced electricity,
and Pouillet and others have proved that the evaporation
must be that of undistilled water. (Do.)
(12.) Evaporation and vegetation are great sources of
the electricity of the atmosphere. (Her&ch. 127.)
(13.) Friction is probably one of the causes of atmo-
spheric electricity. Evaporation is a more powerful source,
but it must be accompanied by chemical decomposition.
Combustion and vegetation are also sources. (Kaem. 336.)
(14.) "It is considered that electricity is being per-
12 LIGHTNING.
I. C I 1522.
petually evolved from the earth (as from a huge electric
machine) by the incessant changes in the mechanical as
well as chemical condition of its constituents ; such changes
for instance as those accompanying variations of tempera-
ture produced by the enormous extent of evaporation from
the land and fresh water as well as from the ocean by the
absorption and re-irradiation of solar heat ; by the escape
of central heat ; or by the decomposition and recomposition
perpetually in progress over the face of the earth, of all
descriptions, from slow putrefaction to rapid combustion,
&c., &c., all of which are more or less associated with
changes in electric condition." (Nets. A. M.}
(b) Rain and Sail.
(15.) D'Alibard and Franklin found that every shower
of rain is accompanied by electricity. (Kaem. 328.)
(16.) Rain and (especially) hail are probably causes
of lightning. The electriferous globules of the clouds
coalesce into rain, and a sudden increase of electric tension
results. Each great flash of lightning is generally suc-
ceeded by a sudden rush of rain. (HerscJi. 131.)
(17.) The condensed vapours liberate electricity. Rain
or hail follows flashes of lightning. These are the effect
of rain rather than the cause of it. (Kaem. 368.)
(18.) Rain falling during thunderstorms contains nitric
acid. (Ar. 64.)
(19.) Thundery weather is known to turn milk sour, to
spoil beer, and to hasten the corruption of meat. (Do. 98.)
(20.) " The formation of hail appears to be indisputably
connected with the presence of an abundant quantity of
fulminating matter in the clouds." (Do. 235.)
(21.) Hail commits great ravages in France on agricul-
ture, and especially in the vine districts. (Do. 233.)
(22.) The use of pointed captive balloons is suggested
by Arago in order to dissipate hailstorms and thunder-
storms. (Do.}
NOTES ON LIGHTNING. 13
I. C 023 32.
(23.) " Hailstorms are those in which the development
of electricity attains the largest proportions. The thick
clouds in which the meteor becomes elaborated are laden
with a large quantity of electrical fluid." (Flam. 442.)
(24.) Hail is formed of globules of ice, and generally
precedes thunderstorms. It is not well accounted for.
(Gan. 816824.)
(25.) It generally falls in the hottest time of day, and
in spring or summer. (Do.}
(26.) Electricity is present in dew, fog, and snow.
(JTaem. 342.)
(c) Clouds.
(27.) Cloud is only fog. Fog is always in a compara-
tively high electric state. (Hersch. 129.)
(28.) The following heights of thunderclouds have been
observed :
By De L'Isle, at Paris, in 1712 .... 26,510 feet.
Abbe Chappe, at Tobolsk, in 1761 . . 10,960
Lambert, at Berlin, 1773 . . . { ^
Le Gentil, at Mauritius .... 2,953
,, Pondicherry, in 1769 . . 10,827
D'Abbadie, at Abyssinia, in 1843 5 . ( a f Q l\
( O,DOU )
Once in Austria (See incident No. 3, Chap. III.) 92
(Ar. 17.)
(29.) Thunderclouds are about 1,300 to 1,400 yards
distant from the earth in winter, and 3,300 to 4,400 in
summer. (Gan. 816 824.)
(30.) The thickness of a low-lying stormcloud at Gratz,
in Austria, on 15th June, 1826, was found to be 120 feet.
(And. 69.)
(31.) Clouds approach each other either by electric
action, or when driven by winds. (Harr. 59.)
(32.) Wind and electric attraction tend to make the
clouds approach the earth. (Mann. 1875, 531.)
14 LIGHTNING.
I. C<Z33 41.
(33.) When a charged thundercloud " is generated in
the upper regions of the air, and hemmed round by its
incumscribing insulation, all the complicated phenomena
of induction immediately appear." (Do. 530.)
(34.) " The broad masses of insulated clouds are con-
ductors ready to receive large charges .... the surround-
ing spaces of clearer and drier air are the insulators that
imprison the accumulating charge, and the vapours that
ascend from the earth and drift in with the winds from
side regions are the carriers and feeders of the charge."
(Do.)
(35.) " The real function of the cloud is simply the
bringing into continuous electrical communication a wide
stretch of electrically charged air." (Do.)
(36.) "When a stormcloud hangs low over the earth,
the negative reaction of that part of the ground is very
largely intensified by induction." (Do.)
(d) Terrestrial Electricity.
(37.) "When the atmosphere is tempestuous, there are
simultaneously great perturbations in the interior of the
earth, and at the surface, or below the surface of waters."
(Ar. 93.)
(38.) Cases have happened during thunderous weather
of surfaces of springs and wells being troubled, of inun-
dations being caused, and of subterraneous noises. (Do.
94.)
(39.) By the influence of a thunderstorm, flames may be
developed under water, and shoot upwards from its surface.
(Do. 100.)
(40.) It cannot be doubtful that local circumstances
influence the frequency of thunderstorms. (Do. 115.)
(41.) Mr. L. W. Dillwyn, writing in 1803, considers that
limestone regions are more subject to thunderstorms than
others. (Do. 116.)
NOTES ON LIGHTNING. 15
I. 04251.
(42.) The course of lightning is influenced by the ter-
restrial bodies near which it explodes. (Do. 92.)
(43.) Thunderclouds often follow the course of rivers.
(Do. 7.)
(44.) " There can be no doubt that thunderstorms will
visit some districts in preference to others, and that light-
ning will descend constantly on some selected spots, and
will entirely keep away from others." (And. 63.)
(45.) " There can be no doubt, from thousands of obser-
vations made, that it is one of the characteristics of the
electric force to seek its way towards waters." (Do. 69.)
(46.) The surface of the earth is one of the terminating
planes of the electrical action. (W. 0. 1858. App. E. 4.)
(47.) The terminating electric plane of a lightning
discharge is sometimes beneath the surface of the ground.
(Do. 1875, 2.)
(48.) Light dry soils, such as shingle and sand, are to
be regarded as non-conducting matter resting on the
electric surface. (Do. 3.)
(49.) The electricity on the earth's surface is induced by
the clouds. (Harr. 11 et passim.}
(50.) " The potential of the earth's surface is assumed
as the zero or datum level from which all other potentials
are measured ; nevertheless we know that the potentials of
different places on and in the earth differ considerably,
sometimes to the extent of several hundred volts, though
this is rare. We obtain this information from the currents
observed to flow through wires joining parts of the earth
widely separated." (Jen. 365.)
(51.) "Not much is known of the distribution of elec-
tricity on the surface of the earth. According to Sir
Win. Thomson the most probable distribution is analogous
to that which would be produced if the earth's surface
generally were charged with negative electricity held as a
charge on the inner armature of a condenser, the outer
armature of which was in the upper regions of the atmo-
sphere, the lower part of which acts as a dielectric." (Do.)
16 LIGHTNING.
I. C e 52- 60.
(52. ) The earth has been named the common reservoir
of electricity. (Gan. 58.)
(53.) " Peltier drew the conclusion from his experiments
' that the earth itself, and more particularly the fiery
liquid mass forming the inner bulk of it, over which the
solid crust and the ocean lie, both thinner in comparison
than the skin of an apple, forms one immense reservoir of
electricity.' As light comes from the sun, generated as we
believe by heat, so the electric force, he held, comes from
the interior of the globe, likewise generated by heat."
(And. 71.)
(54.) " On the whole, Peltier's explanation, such as it is,
may fairly be accepted, in the present state of scientific in-
vestigation, as one of the bestthatcan be given." (Do. 72.)
(e) Earih Currents.
(55.) Earth currents are irregular currents of electricity
which manifest themselves by abnormal disturbances of
telegraphs. (Gan. 837.)
(56.) Sabine considers earth currents are magnetic dis-
turbances " due to a peculiar action of the sun, and pro-
bably independent of its radiant heat and light." (Do.)
(57.) Balfour Stewart considers earth currents as secon-
dary currents due to small but rapid changes in the earth's
magnetism. (Do.)
(58.) Earth currents are constantly passing through the
telegraph wires, ' ' due to the varying potential of different
parts of the earth's surface." ( Cull. 28.)
(59.) Earth currents depend " either on difference of
potential between the earth at the two stations or on induc-
tion from passing clouds." (Jen. 310.)
(60.) Powerful earth currents were experienced on tele-
graph lines in Ireland and Scotland on August 12th, 1880.
On the same day there was a thunderstorm in the S.W. of
Ireland, and on the night of that day a brilliant aurora
NOTES ON LIGHTNING. 17
I. C/60a 64.
was seen in Aberdeen and other parts of Scotland, and a
violent thunderstorm occurred at Vienna. (Stand. 14/8/80.
Tel. 1/9/80.)
(60.) " Magnetic observations are complicated by the
existence of certain currents of electricity which move in
the earth." (Gord. i. 199.)
(605.) Mr. C. V. Walker, F.B.S., published in 18612
a series of investigations on earth currents, and determined
therefrom :
1st. " That currents of electricity are at all times
moving in definite directions in the earth."
2nd. " That their direction is not determined by local
causes."
3rd. " That there is no apparent difference, except in
degree, between the currents collected in times of great
magnetic disturbance, and those collected during the ordi-
nary calin periods."
4th. ' ' That the prevailing directions of earth currents
or the currents of most frequent occurrence are approxi-
mately N.E. and S.W. respectively." (Do.)
(/) The Earth's Magnetism.
(61.) " Magnets are substances which have the property
of attracting iron, and the term magnetism is applied to
the cause of this attraction, and to the resulting phenomena."
(Gan. 557.)
(62.) " Magnetic substances are substances which, like
iron, steel, and nickel, are attracted by the magnet." (Do.
562.)
(63.) " The earth acts as a great magnet. Dr. Gilbert,
of Colchester, made that clear nearly three hundred years
ago." (Thorns. Tel. 15/1/74.)
(64.) "The declination is accidentally disturbed in its
daily variations by many causes, such as earthquakes, the
aurora borealis, and volcanic eruptions. The effect of the
18 LIGHTNING.
I. 06569.
aurora is felt at great distances. Auroras which are only
visible in the north of Europe act on the needle even in
these (Paris) latitudes, where accidental variations of 20'
have been observed. In polar regions the needle fre-
quently oscillates several degrees ; its irregularity on the
day before the aurora borealis is a presage of the occur-
rence of this phenomenon." (Gan. 567.)
(65.) " Another remarkable phenomenon is the miscel-
laneous occurrence of magnetic perturbations in very dis-
tant countries. Thus Sabine mentions a magnetic disturb-
ance which was felt simultaneously at Toronto, the Cape,
Prague, and Yan Diemen's Land. Such simultaneous
perturbations have received the name of magnetic storms."
(Do.)
(66.) " The magnetic intensity increases with the lati-
tude. Humboldt found a point of minimum intensity on
the magnetic equator in Northern Peru." (Do. 573.)
(67.) "Observations have led to the discovery that the
magnetism of the earth is in a state of constant fluctuation
like the waves of the sea." (Do. 574.)
(68.) " Ampere assumes that each individual molecule
of a magnetic substance is traversed by a closed electric
current." .... "The resultant of the actions of all
the molecular currents is equivalent to that of a single
current which traverses the outside of a magnet." (Do.
719.)
(69.) "In order to explain on this supposition terrestrial
magnetic effects, the existence of electrical currents is as-
sumed which continually circulate round our globe from
east to west perpendicular to the magnetic meridian. The
resultant of their action is a single current traversing the
magnetic equator from east to west. These currents are
supposed to be thermo-electric currents due to the variations
of temperature caused by the successive influence of the
sun on the different parts of the globe from east to west.
These currents direct magnetic needles and impart a
natural magnetisation to iron minerals." (Do.)
NOTES ON LIGHTNING. 19
I. C 70735.
(70.) As regards the distribution of the magnetic force
on the surface of the earth, "it is conceivable that this
force may be wholly due to currents flowing round the
earth, and maintained by the thermo-electric action of the
sun, or to some other cause connected with the rotation of
the earth." (Jen. 367.)
(71.) "It is one of the greatest mysteries of science.
.... What can be the cause of this magnetism in the in-
terior of the earth ? . . . . Electric currents afford the more
favourable hypothesis. . . . But what sustains the electric
currents ? . . . . We have none of the elements of the pro-
blem of thermo-electricity in the underground temperature
which could possibly explain, in accordance with any
knowledge of thermo-electricity, how there could be
sustained currents round the earth." (Thorns. Tel.
15/1/74.)
(72.) "It was suggested by the great astronomer
(Halley) that there is a nucleus in the interior of the
earth, and that the mystery is explained by a magnet not
rigidly connected with the upper crust of the earth, but
revolving round an axis of figure of the outer crust, and
exhibiting a gradual precessional motion independent of
the precessional motion of the outer rigid crust." (Do.)
(73.) "If we could have simultaneous observations of
the underground currents, of the three magnetic elements,
and of the aurora, we should have a mass of evidence from
which, I believe, without fail, we ought to be able to con-
clude an answer more or less definite to the question I
have put." (Do.}
(73.) " There is no doubt that the earth is affected by
electrical phenomena occurring in the sun." (Gord.
i. 21.)
(735.) Professor Balfour Stewart has pointed out that the
magnetic storm of unprecedented magnitude that occurred
in August and September, 1859, was synchronous with the
period of maximum activity of one of the largest sun-spots
ever observed. (Do. 197.)
20 LIGHTNING.
I. 0^74 82.
(g) Aurora.
(74.) Aurora is "a remarkable luminous phenomenon,
which is frequently seen in the "atmosphere at the two
terrestrial poles." (to. 837.)
(75.) " The constant direction of their arc as regards the
magnetic meridian, and their action on the magnetic needle
show that they (aurorse) ought to be attributed to electrical
currents in the higher regions of the atmosphere." (Do.)
(76.) " This hypothesis is confirmed by the circumstance
observed in France and other countries on August 29th
and September 1st, 1859, that two brilliant auroree boreales
acted powerfully on the wire of the electric telegraph."
(Do.)
(77.) " According to M. De la Eive, the auroree
boreales are due to electric discharges which take place in
Polar regions between the positive electricity of the atmo-
sphere and the negative electricity of the terrestrial globe;
electricities which themselves are separated by the action
of the sun on the equatorial regions." (Do.)
(78.) "The aurora borealis is one of the grand results
of atmospheric electricity. Instead of a furious and violent
storm limited to a few leagues, it is a gentle and gradual
recomposition of the negative fluid of the earth with the
positive fluid of the atmosphere taking place in the aerial
heights, in the upper hydrogenous atmosphere. This dis-
engagement of electricity in a vast sheet is only visible at
night." (Flam. 497.)
(79.) " We have the strongest possible reason for be-
lieving that aurora consists'of electric currents." (Thorns.
Tel. 15/1/74.)
(80.) "Aurora borealis is properly comparable with the
phenomenon presented by vacuum tubes." (Do.)
(81.) Magnetic storms are always associated with aurorse.
(Do.}
(82.) " According to Balfour Stewart, aurorse and earth
currents are to be regarded as secondary currents due to
NOTES ON LIGHTNING. 21
I. C h 83 89.
small but rapid changes of the earth's magnetism; he
likens the body of the earth to the magnetic core of a
BuhmkorfFs machine, the lower strata of the atmosphere
forming the insulator, while the upper and rarer, and
therefore electrically conducting, strata may be considered
as the secondary coil. On this analogy the sun may per-
haps be likened to the primary current which performs the
part of producing changes in the magnetic state of the
core." (Gan. 837.)
(83.) "It is principally in the neighbourhood of the
Polar circle, where thunderstorms are rare, that these mani-
festations of terrestrial electricity are seen to the fullest
advantage." (Flam. 497.)
(84.) "A French scientific commission to the North
observed one hundred and fifty aurorse in two hundred
days." (Gan. 836.)
(85.) "They are visible at a considerable distance from
the Poles and over an immense area. Sometimes the same
aurora borealis has been seen at the same time at Moscow,
Warsaw, -Rome, and Cadiz." (Do. 837.)
(h} St. Elmo's Fires.
(86.) In thunderstorms the projecting parts of bodies,
and especially the metallic parts, sometimes shine with
rather a vivid light. This light is called St. Elmo's Fire.
(Ar. 102.)
(87.) " The St. Elmo's Fires are a slow manifestation of
electricity, a quiet and steady outflow which radiates gently
over the topmost parts of lightning conductors of buildings
and vessels during thunder weather, when the terrestrial
electric tension is strongly attracted by that of the clouds."
(Flam. 493.)
(88.) " The 'electric glow' is from a negatively electri-
fied pointed conductor." (Tynd. 92.)
(89.) The glow is sometimes seen on the masts of ships, and
it is mentioned by the ancients as appearing on the points
22 LIGHTNING.
I. C t 9099.
of lancea. It is called St. Ermo's, or St. Elmo's Fire, after
the sailor's saint, Erasmus, who suffered martyrdom at
Gaeta at the beginning of the fourth century." (Do.}
(90.) Nitrogen gas has the greatest power of originat-
ing this luminous appearance when it is artificially formed.
(Harr. 45.)
(91.) St. Elmo's Fires are several times mentioned by
Pliny, Seneca, Csesar, and Livy. English sailors call them
" comazants." (Do. 19.)
(92.) In January, 1748, several comazants settled on the
spindles of the masts of the merchant ship Dover, and burnt
like large torches. (Do.)
(93.) In May, 1821, in the North Atlantic Ocean, be-
tween Bermuda and Halifax, St. Elmo's Fireswere observed
on the masts of H.M.S. Newcastle. (Do.}
(94.) Priestley's " History of Electricity " states that the
cross of the church steeple of Plauzet, in France, always
during thunderstorms had its three pointed extremities
surrounded with a body of flame. (Do.)
(95.) St. Elmo's Fires are often seen over the spires of
Notre Dame, Paris, during violent thunderstorms. (Flam.
494.)
(96.) On the 2nd March, 1869, the cross on the steeple
(130 feet high) of the Church of St. Catherine de Fier-
bois, Chinon, France, appeared, towards the end of a
storm, with " a crown of fire " around it. No thunder had
been audible. (Do.)
(i) Waterspouts.
(97.) Waterspouts "are masses of vapour suspended in
the lower layers of the atmosphere, which they traverse,
and endowed with a gyratory motion." (Gan. 819.)
(98.) Waterspouts are generally accompanied by hail
and rain, and often emit thunder and lightning. (Do.)
(99.) "When they take place on the sea .... the water
is disturbed and rises in the form of a cone, whilst the clouds
NOTES ON LIGHTNING. 23
I. k 100105.
are depressed in the form of an inverted cone ; the two
cones then unite to form a continuous column from the sea
to the cloud." (Do.)
(100.) The origin of waterspouts is not known. " Peltier
and many others ascribe to them an electrical origin."
(Do.)
(101.) At Illinois, U.S., on the 4th of June, 1814, Mr.
Griswold observed a waterspout with incessant lightning
between the clouds and the earth near the surface of the
spout; but no thunder was heard. (Ar. 155.)
(102.) At Banbury, in England, on the 3rd of December,
1872, what was at first supposed to be a " fireball " was
seen by four persons from different points. It appears to
have been a whirlwind of vapour or waterspout, accom-
panied by a whizzing sound, sulphurous smell, and sparks
or flashes, rising high into the air, and passing about six
to ten feet over the ground for about two miles, uprooting
trees on its way, till, at a place where the ground had the
appearance of being cut up by a cannon ball, it vanished.
(S.T.K 371.)
(103.) A waterspout was seen on the rifle ranges at
Norwich in July, 1880. It lasted half an hour. (Graph.
24/7/80.)
(104.) A waterspout passed over Gower, in Glamorgan-
shire, on the 22nd July, 1880. Thunderclouds had pre-
viously gathered. It consisted of a large slender column
of dense vapour or rain descending from the clouds to the
earth, and lasted about five minutes, when it was absorbed
in heavy black clouds, and these then discharged for about
an hour a perfect deluge of rain. (8. M. M. August, 1880.)
(k) Earthquakes.
(105.) The proximate cause of earthquakes " seems
referable to the action of internal heat or fire." (Enc. Br.
Art. Earthquake.}
24 LIGHTNING.
I. 106112.
(106.) " There is good reason for holding that earth-
quakes are closely connected with volcanic agency. Both
probably spring from the same cause." (-O0.)
(107.) " Whilst the action of water has been generally
to wear down, transport, and redeposit in nearly regular
and horizontal order, or in other words, to restore the level
of the earth's surface, the action of heat has, in conjunc-
tion with electricity, &c., tended to disturb that level, and
to raise some portions of the surface above others."
(Portl. A.M.]
(108.) " The facts of disturbance are palpable, and the
nature of the forces producing them can be inferred by
reasoning, though not demonstrated by observation.
Electricity may be fairly classed with such forces, and
yet it may only be a secondary cause ; but assuredly ample
reason has been adduced for the assumption that heat must
at least be a primary one." (-00.)
(109.) "Mr. Howorth quotes from Dr. Zollner's paper
in the Philosophical Magazine on the subject of the correla-
tion of earthquakes with magnetic disturbance, wherein it
is stated that Kriel has given many cases where magnetic
disturbances coincide with earthquakes ; hence he thinks
connection between the two phenomena probable." (Tel.
15/9/74.)
(110.) In 1822, there occurred in France, and over a
great part of the Continent, " an extraordinary number of
violent thunderstorms, accompanied by earthquakes and
simultaneous eruptions of Mount Vesuvius, the latter on a
scale not witnessed for centuries." (And. 76.)
(1100.) A great earthquake occurred in Chili in 1822.
(Portl A.M.]
(111.) At the earthquake or upheaval of Sabrina, a
small island among the Azores, in 1811, Captain Tillard
observed columns of dust and ashes and much lightning.
(Ar. 12.)
(112.) Cuvier asserts that "both men and animals suffer
from a certain malaise during the period of these convul-
NOTES ON LIGHTNING. 25
i. cnis 117.
sions, and he attributes the reason to electrical disturbance."
(Stand. 12/11/80.)
(113.) Earthquakes occurred in 1880 as follows: At
Manilla in July, at Smyrna in July, at Valparaiso in Sep-
tember, at Lisbon, Madrid, and other parts of the peninsula
in October, at Agram and over Southern Austria in Novem-
ber and December, and at Odessa, Bucharest, and over South
Eastern Europe in December. (Stand. July Dec. '80.)
(113$.) The shocks of earthquake at Agram in January,
1881, were accompanied by " loud subterranean thunder."
(Stand. 27/1/81.)
(/) Volcanic Eruptions.
(114.) Pliny wrote to Tacitus, A.D. 79, of lightning
attending an eruption of Mount Vesuvius. Padre della
Torre, in 1182, mentions lightnings as often seen there in
the midst of smoke. Bracini relates of the eruption of
Vesuvius in 1631 that frequent lightnings issued from a
cloud of smoke from the crater and killed several persons.
Valetta mentions lightnings happening at the eruption of
1707. The same circumstances are recorded of the eruption
of 1767. (Ar. 11.)
(115.) Sir William Hamilton mentions lightning with-
out thunder at the eruption of Vesuvius of 1779, and with
thunder at that of 1794. A house struck at San Jorio by
the lightning during the latter eruption showed the same
effects as if occasioned by atmospheric lightning. (Do.
12.)
(116.) Earthquakes are a portion of the phenomena of
volcanic eruptions, ' ' the earthquake often preceding the
volcanic eruption, being the result of unusual movements
in the interior of the earth, which is connected with its
surface by the volcano." (Portl. A. M.)
(117.) "The phenomena more nearly preceding an
eruption (of Mount Vesuvius) are the occurrence of earth-
quakes, increasing in intensity and frequency for some
c
26 LIGHTNING.
I. 0118122; Da 16.
days beforehand, also the irregularity of the diurnal
variations of the magnetic needle." (Fras. R. E. P.)
(118.) ' ' One of the remarkable attendants of an eruption
is the frequency of lightning flashes, considered by Dr.
Palniieri to be due to the condensation of the vapour of
water from the crater ; just as in an ordinary thunderstorm
lightning occurs at the time the vapour is condensing, as
is proved by the rain that follows." (-Do.)
(119.) Seneca mentions lightning appearing at an
eruption of Mount Etna. In 1755 lightning attended an
eruption of Mount Etna. (Ar. 12.)
(120.) At a little volcano which appeared in 1831
between Sicily and Pantellaria, columns of black dust
arose with lightning and thunder. (Do. 13.)
(121.) During the earthquakes at Manilla in July, 1880,
all the volcanoes of the island were in eruption. (Stand.
July, 1880.)
(122.) Mount Vesuvius was in eruption in September
and November, 1880. (Do. 9/80 & 11/80.)
(D.) LIGHTNING DISCHARGES.
(a) The Nature of Lightning.
(1.) A thunderbolt is defined as "a shaft of lightning,
particularly if passing in a direction towards the earth."
(Chaml.)
(2.) Seneca defined thunderbolts as lightnings that
reach the ground. (Ar. 24.)
(3.) Foudre (anglice, thunderbolt), is the term exclusively
applied in France to zigzag lightning. (Do.)
(4.) Arago divides lightnings into zigzag, sheet, and
fireballs or globular lightning. (Do.)
(5.) Arago mentions zigzag lightning generally under
the name of " fulminating matter." (Do. passim.)
(6.) Lightning is " simply incandescent matter. It in-
NOTES ON LIGHTNING. 27
I. D7 13.
dicates the path, of the discharge and nothing more."
(Preece, 338.)
(7.) "Maffei, Chappe, and others, deem that lightning
or thunderbolts are almost always elaborated on the
ground ; that it is from the ground they suddenly dart ;
that instead of descending from the clouds to the earth,
their course is on the contrary from the earth to the clouds.
Those who are partisans of this opinion say they have dis-
tinctly seen lightning rise like rockets." (Ar. 101.)
(8.) "It is difficult to conceive the possibility of dis-
tinguishing by the eye whether a flash of lightning
between the clouds and the earth rises or descends." (Do.)
(9.) There are numerous instances of lightning moving
from below upwards. (JKaem. 347.)
(10.) The spark probably leaves both bodies at once.
Kaemtz has actually observed this in the case of two
clouds. (Do.)
(11.) " The lightning discharge is the electrical discharge
which strikes between a thundercloud and the ground.
The latter by the induction from the electricity of the cloud
becomes charged with contrary electricity, and, when the ten-
dency of the two electricities to combine exceeds the resist-
ance of the air, the spark passes, which is often expressed
by saying that a thunderbolt has fallen." (Gan. 828.)
(12.) " Lightning in general strikes from above, but
ascending lightning is also sometimes observed ; probably
this is the case when the clouds being negatively, the
earth is positively electrified, for all experiments show
that at the ordinary pressure the positive fluid passes
through the atmosphere more easily than negative elec-
tricity." (Do. 831.)
(13.) " It is evident, upon ordinary electrical principles,
that if two clouds, or one cloud and the earth, be oppo-
sitely excited and charged, the spark and the discharge
may either pass from the cloud to the earth or from the
earth to the cloud, as circumstances to us imperceptible
may direct." (Lunn, 9.)
c2
28 LIGHTNING.
I. D 1424.
(14.) " People always speak of lightning falling, and
never of its rising or ascending, which must often be the
case." (Graves, 8. T. E. 413.)
(15.) " Lightning is the joint work of the positive and
negative electricity. When the proper conditions obtain
between the earth and the cloud for the production of a flash,
then both the positive and negative exert their utmost
to approach each other, selecting the easiest available
channel, such as trees, bell- wires, church steeples, &c."
(Do.)
(16.) ''Lightning is an enormous electric spark passing
between two clouds, or from a cloud to the earth." (Jen.
105.)
(17.) " In the latter case, the electrified cloud is attracted
towards any prominence or good conductor, which be-
comes electrified by induction, and the spark of lightning
passes when the difference of potential is sufficient to over-
come the mechanical resistance of the air." (Do.)
(18.) "The thunderbolt as a rule falls only during
heavy showers, by taking advantage of the semi-communi-
cation with the earth offered by the vertical series of rain
drops." (Nouel. Tel. 1/9/74.)
(19.) Lightning sometimes escapes from the upper sur-
faces of clouds. (Ar. 40.)
(20.) Lightning exists in our climate without thunder,
in a clear sky, in the shape of "heat lightnings." (Do.
58.)
(21.) Lightning has been known to occur without thun-
der in a cloudy sky. (Do. 59.)
(22.) Fulminating explosions have been produced by
thunderstorms without any luminous appearance. (Do.
98.)
(23.) Thunderbolts often develope by their action smoke,
and generally a sulphurous odour. (Do. 62.)
(24.) " Clouds are not perfect conductors, and therefore
do not part with all their discharge at once. Hence a
single discharge does not deprive a cloud of the whole of
NOTES ON LIGHTNING. 29
I. D25 34.
its charge. There may be several successive discharges.
The electroscope and galvanometer show this." (Preece,
334.)
(25.) <f The evidences concerning ' ball lightning ' are so
numerous that it is impossible to deny that it exists." (Do.
368.)
(26.) " Fireballs are among the most interesting and
mysterious of electrical phenomena." (Lat. Clark,
8. T. E. 371.)
(27.) The striking distance of lightning varies from 650
feet to 6,500 feet. (Mann, 1875, 531.)
(28.) The duration of the flash does not exceed roVo of a
second. (Do.)
(29.) The most brilliant and extensive flashes have not
a duration equal to the r - -Vo- of a second. (Ar. 48.)
(30.) The following lengths of flashes have been ob-
served :
In Abyssinia, by M. D'Abbadie . . . 3'7 miles.
In Toulouse, by M. Petit . . . . 9-6
In Weimar, by M. Weissenborn 6'2
(Do. 169.)
(31.) Lightning finds a path of least resistance; hence
the zigzags, and the length of the flashes, often several
miles. (Sersch. 133.)
(32.) Lightning always takes what is technically called
the " line of least resistance." (And. 142.)
(33.) When lightning strikes an object it frequently
divides into several distinct forks or channels. (Lat.
Clark, S.T. E. 371.)
(34.) " In the tropics a heavily charged cloud does not
generally discharge its electricity in a single ray as it
does in countries of moderate climate ; on the contrary,
it frequently takes place from a central point in many
radial directions at the same time." (Treu. S. T. E.
377.)
30 LIGHTNING.
I. D I 3546.
( 1} The Action of Lightning on Materials.
(35.) Cceteris parilus, the highest points are those which
lightning strikes by preference. (Ar. 139.)
(36.) " It is only as it enters metallic bodies, or at the
moment of quitting them, that lightning produces much
damage." (Do. 140.)
(37.) Lightning often fuses metals, not by ' ' cold fusion,"
but by heating them like ordinary fire. (Do. 66.)
(38.) It sometimes contracts metallic wires. (Do. 75.)
(39.) It sometimes fuses and then vitrifies earthy sub-
stances. (Do. 78.)
(40.) Lightning can transport bodies. (Do. 86.)
(41.) Its action imparts magnetism ; and in passing near
a compass needle it affects its magnetism, and sometimes
inverts its poles. (Do. 88, 89.)
(42.) It forms " fulgurites " by striking sand, fusing
it, and giving it the form of vitrified hollow tubes. Some
of these tubes have been found 30 or 40 feet long. (Do.
79.)
(43.) Fulgurites is fused quartz due to lightning striking
sand. (Hersch. 135.)
(44.) " The shivering of trees into small splinters like a
broom is probably owing to the rarefaction of the sap in the
longitudinal pores, or capillary pipes, in the substance of the
wood, and the blowing up of bricks or stones in a hearth,
rending stones out of a foundation, and splitting of walls,
are also probably effects sometimes of rarefied moisture in
the earth, under the hearth, or in the walls." (Frank. 429.)
(45.) Bodies such as air, glass, resins, dry wood, stones,
and substances generally which resist the progress of dis-
charge, involve an explosive form of action attended by
light, heat, and an enormous expansive force. (W. 0.
1858, App.A. 2.)
(46.) " It is, in fact, this terrible expansive power which
we have to dread in cases of buildings struck by lightning,
NOTES ON LIGHTNING. 31
I. DC 47 54.
rather than the actual heat attendant on the discharge
itself." (Do. 6.)
(47.) With metallic substances the expansive action of
lightning ceases. (Do. 3.)
(48.) The particular faces of a building that are most
exposed to be struck are perhaps those most exposed to the
prevailing winds of a country during thunderstorms. (Ar.
198.)
(49.) Nollet says that cater is parlous, spires covered with
slates are more often struck than those built with stone.
This is probably on account of the metal nails and wooden
laths used in fixing the slates. (Do. 199.)
(50.) It is futile to consider low elevation of buildings
as an absolute safeguard. (Do.)
(c) Return Strokes.
(51.) " Many persons who are killed by lightning are
killed by the simple shock resulting from the sudden dis-
charge of electricity from their bodies, which had been
inductively electrified from the clouds ; the lightning pass-
ing from cloud to cloud discharges these, and the escape of
the electricity from the body previously charged produces
the shock." (Jen. 363.)
(52.) " Lord Mahon fused metals and produced strong
physiological effects by the return stroke." (Tynd. 106.)
(53.) "In nature, disastrous effects may be produced
by the return stroke. The earth's surface, and animals
or men upon it, may be powerfully influenced by one
end of an electrified cloud. Discharge may occur at the
other end, possibly miles away. The restoration of the
electric equilibrium by the return stroke may be so violent
as to cause death." (Do.)
(54.) "It was the action of the return shock upon a dead
frog's limbs, observed in the laboratory of Professor
Galvani, that led to Gralvani's experiments on animal
32 LIGHTNING.
I. D d 5564.
electricity, and led further to the discovery by Volta of the
electricity which bears his name." (Do.)
(55.) Return shock is "a violent and sometimes fatal
shock which men and animals experience, even when at a
great distance from the place where the lightning discharge
passes. This is caused by the inductive action which the
thundercloud exerts on bodies placed within the sphere
of its activity." ( Gan. 832. )
(56.) " These bodies are then charged with the opposite
electricity to that of the cloud ; but when the latter is dis-
charged by the recombination of its electricity with that of
the ground the induction ceases, and the bodies reverting
rapidly from the electrical to the neutral state, the concus-
sion in question is produced." (-00.)
(57.) " The return shock is always less violent than the
direct one ; there is no instance of its having produced any
inflammation, yet plenty of cases in which it has killed
both men and animals." (Do.)
(58.) " The shocks experienced by living people on the
instant of a discharge of lightning without fatal results are
generally 'return shocks.' " (Mann, 1875, 539.)
(d) The Effect of Lightning on Persons,
(59.) People killed by lightning suffer no pain. (Tynd.
99.)
(60.) Persons struck see previously no lightning. (Ar.
13.)
(61.) The most frequent result of non-fatal strokes is
partial paralysis of the legs or arms. (Do. 256.)
(62.) Instances have occurred of the hair being burnt
off persons in non-fatal strokes. (Do.)
(63.) Moderate strokes frequently appear to rid men and
animals of maladies. (Do. 258.)
(64.) Moderate strokes have been known to accelerate
the growth of trees. (Do.)
NOTES ON LIGHTNING. 33
I. D e 6570.
(65.) " Lightning, Death from. The body in these cases
retains its warmth for some time, even after death has
actually taken place. The first thing to be done is to
strip off the clothes and dash cold water upon the trunk in
considerable quantities for ten or fifteen minutes ; this, in
slight cases, will speedily bring about a reaction. The
body should also be assiduously rubbed, and artificial
respiration be effected. Stimulants of the most active kind
are to be resorted to, but that of electricity or galvanism
is the one specially called for in this modification of
asphyxia." (Shaw, 77.)
(e) The Effect of Lightning on Telegraphs.
(66.) The accidents that telegraphs suffer from might
be divided into three classes :
"1. Those affecting the wires."
"2. Those affecting the poles."
" 3. Those affecting the instruments."
(Preece, 342.)
(67.) " Each of these classes may be divided into those
which are the result of direct discharge, and those which
are the result of induction." (-00.)
(68.) "In the first case, the wires, poles, or instruments
form a path or circuit for a portion of the discharge itself ;
in the second case, they are influenced by currents which
are induced by the approach, recession, or sudden neutral-
isation of charged clouds." (Do.)
(69.) "The direct effects are not nearly so numerous as
the induced." (Do. 343.)
(70.) As regards induced effects during a thunderstorm,
wires are pervaded by repeated currents which ring bells,
demagnetise needles, throw apparatus out of adjustment,
c3
34 LIGHTNING.
I. D71 79.
shock clerks, and make false signals on railway block in-
struments." (-#0.)
(71.) During the construction of the Husac tunnel, two
premature explosions of blasting charges were caused by
induced currents, producing fatal effects, (Do.)
(72.) " Not only are the overground wires affected, but
those buried two feet deep underground." (Do.)
(73.) " Sometimes poles have been shivered, but usually
a discharge which has taken the wire in its path divides
itself among several poles, and cuts out with the smooth-
ness of a gouge grooves from the top to the bot-
tom." (Do.)
(74.) Mr. S. A. Yarley's carbon, or " lightning bridge "
protector is in use with post-office instruments. (Do.
350.)
(75.) In India, where thunderstorms are far more intense
than in England, " every office is protected by earth-plates
separated from line-plates by a thin layer of air, the
interval being maintained by thin ebonite washers." (Dr.
Werner Siemens' plate dischargers.) The posts are of
iron. Accidents are rare. (Do. 352.)
(76.) Some submarine mines used in the defence of
Venice and Pola were exploded from the sudden develop-
ment of induced currents in the mines. (Abel, S. T. E.
374.)
(77.) Instruments are sometimes damaged in India by
currents not sufficient to charge the upper plate of the
Siemens' discharger to a " sparkling potential." (Ayrt,
S. T. .363.)
(78.) An atmospheric discharge of very high potential
" will jump from the line wire to the insulator stalks if
they be connected with the earth, smashing the insulators
in its path." (Do.)
(79.) On the 4th July, 1871, at the underground tele-
graph line on the Manchester and Liverpool railway,
whilst a jointer, during a thunderstorm, was jointing
some wires, he found that sparks were given off to
NOTES ON LIGHTNING. 35
I. E 17.
his jointer's box while resting on the ground. (Mr.
G. E. Preece, S. T, E. 356.)
(E.) THE INFLUENCE OF METALS ON LIGHTNING.
(1.) One of the objects of Sir. "W. Snow Harris's treatise,
as stated in his preface, was "to remove the misapprehen-
sion which exists as to the attractive effect of metallic
bodies in storms of lightning." (Harr. Pref.)
(2.) "In every instance of damage to buildings or
shipping by lightning, the cause of the electrical discharge
is determined in a similar way, through points presenting
the least resistance to its progress, and the mischief in-
variably occurs between detached masses of metal." (Do.
88.)
(3.) "When a charged thundercloud hangs low over
the earth, all projecting bodies rising from the ground are
most powerfully influenced by the inductive aciton, and
conducting bodies such as rods, tubes, and sheets of metal
more powerfully than bodies that have less conducting
capacity." (Mann, 1875, 531.)
(4.) Metals have no attraction or affinity for lightning.
(W. 0. 1858, App. A. 9.)
(5.) Lightning falls on trees, rocks, and buildings,
whether they have metal about them or not. (Do.)
(6.) Alluding to the village church of Eosenberg in
Carinthia, Austria, which was repeatedly struck in the
seventeenth and eighteenth centuries, before rods were
known, " very possibly there were large pieces of metal
on the wall or in the roof ; or if not, there may have
been masses of water near, underground, sufficient to
account for the manifestation of the electric force."
(And. 64.)
(7.) "As the use of metals, especially iron, in the con-
struction of buildings, both exterior and interior, is rapidly
extending, this becomes a very important consideration iii
36 LIGHTNING.
I. E 812 ; F 13.
planning the design of lightning conductors." (Do.
140.)
(8.) A human body may form a path of least resistance
between insulated metals in a building, and thus may re-
ceive a discharge. (Do. 160.)
(9.) " Practical experience has pretty fully proved that
an electric discharge has a very great affinity for all metal
bodies, whether they are insulated from the earth or con-
nected with it." (Do. 168.)
(10.) Quoting Dr. Holtz, of Greisswald, "there can be
no doubt whatever that the large increase of the use of
metals in the construction and ornamentation of modern
houses has led to far greater damage to which they are
exposed from lightning." (Do. 225.)
(11.) " Lightning seeks out by preference metallic sub-
stances, whether external or concealed, which are either at
or near the point towards which it falls, or near its subse-
quent serpentine course." (Ar. 139,)
(12.) When there are several metallic masses on a roof
separated from each other, "it is difficult or impossible to
say which of them will be struck by preference," therefore
the safe plan is to unite them all metallically to the con-
ductor. (Do. 224.)
(F.) PRESERVATIVES FROM LIGHTNING.
(1 .) Pliny relates that the ancients believed that thunder-
bolts never penetrated beyond 6 feet below the surface of
the ground, and that they regarded most caves as asylums,
(Ar. 188.)
(2.) Suetonius relates that the Emperor Augustus
retired into a vault when thunderstorms were foreseen.
(Do.)
(3.) Kaempfer relates that the Emperors of Japan have
similar ideas. (Do. 189.)
NOTES ON LIGHTNING. 37
I. F4 14.
(4.) The Romans covered their tents with sealskins as
preservatives. The Emperor Augustus always wore one.
(Do. 190.)
(5.) The Chinese consider that mulberry and peach
trees preserve against lightning. (Do. 191.)
(6.) Mr. Hugh Maxwell, writing in 1787 of his American
experience, says of trees :
Elm . .
Chestnut .
Oak _ ^ ] Often struck.
Pine .
Ash / Rarely.
Beech J x
Birch \ Never.
Maple )
(Do.)
(7.) M. de Thury has met with instances in his French
experience of the following trees being struck : viz. beech,-
pine, fir, cherry, acacia, elm, oak, and poplar. (Do.
192.)
(8.) Pines and resinous trees are said to be less dan-
gerous than oaks and elms. (Gan. 131.)
(9.) Men are often struck in the middle of open plains.
(Ar. 192.)
(10.) Facts show that under trees the danger is still
greater. (Do.)
(11.) Dr. Winthrop suggested (and Franklin approved
the idea) that one ought to place oneself from 16 to 40
feet from a large tree, or intermediate between two trees
at this distance. (Do.)
(12.) Henley also approved, and, in the case of only
one tree, recommended a distance of five or six yards
beyond the extremities of the largest branches. (Do.)
(13.) The best thing to do in a storm is to lie flat on the
ground and not to mind getting wet. (Mann, 1878,
338.)
(14.) There is danger in moving when caught in the
open air in a thunderstorm, and the inconvenience of
getting wet by remaining stationary should be balanced
38 LIGHTNING.
I. F. 1521.
against the chances of lessening the risk of being struck.
(Ar. 199.}
(15.) The danger of being struck is sensibly increased by
metals attached to the person. (Do. 194.)
(16.) Persons afraid of lightning have made glass cages
as asylums. (Do. 193.)
(17.) Franklin recommended the following precautions
to be adopted in houses :
(a.) Avoid the neighbourhood of fireplaces, as light-
ning often enters by the chimney.
(b.) Avoid also metals, including gildings, mir-
rors, &c.
(c) The best place, consistently with (a) and (#), is the
middle of the room.
(d) The less the contact with walls and floors, the less
the danger. A hammock suspended by silken
cords in the middle of a large room is good.
(e) Keep generally near substances which are bad
conductors, such as silk, glass, pitch, mattresses,
&c. (Do. 198.)
(18.) Volta thought large fires would prevent thunder-
storms. (Do. 212.)
(19.) At Caserna, in Eomagna, by the advice of the cure,
the inhabitants on the approach of thunderstorms used to
place heaps of straw and brushwood at about every 50
feet, and set them on fire, and for three years they ex-
perienced no thunder nor hail. (Do.)
(20.) Sailors believe that the firing of artillery disperses
thunderclouds, and agriculturists, in some French districts,
also think so ; but the bombardments of Rio Janeiro in
1711, and of Dannholm, near Stralsund, in 1806, both
events that occurred during thunderstorms, failed to dis-
perse, them and equally powerless is the constant prac-
tice of the Artillery School at Vincennes. (Do. 214.)
(21.) An idea has prevailed in France that ringing
NOTES ON LIGHTNING. 39
I. G 18.
church bells during a thunderstorm was efficacious. This
was based on superstition, the bells having been blessed.
On the contrary, bell-ringers incur danger from lightning.
(Do. 219.)
(G.) STATISTICAL AND GEOGRAPHICAL NOTES.
(1.) During the 50 years from 1793 to 1843 more
than 253 of H.M. ships are known to have suffered.
(Harr. Preface.}
(2.) Mainly during the 16 years from 1799 to 1815,
150 cases have happened of British ships being struck,
70 seamen have been killed, 133 wounded, 100 lower
masts (with corresponding topmasts and smaller spars)
have been destroyed, and damage has been done to the
value of 100,000. (Do.)
(3.) In the 6 years from 1809 to 1815, 30 British
line-of -battle ships, and 15 frigates, were more or less
disabled from lightning. (Do.)
(4.) In 15 months of the years 1829-30, 3 British liners,
1 frigate, and 1 brig, were more or less disabled. (Do.)
(5.) The average annual damage done by lightning in
England alone was estimated in Nicholson's Journal of
Science (in 1843) as 50,000. (Do.)
(6.) Previous to 1872, the average annual number of
deaths in England from lightning was 18, and in France,
95. (Preece, 836.)
(7.) According to Mr. Symons, the meteorologist, in two
storms in June 1872, 200 separate accidents came to his
notice, involving 10 persons killed, 33 persons injured, 60
houses struck, of which at least 10 were burnt down, 23
horses and cattle, and 99 sheep, killed. (Do.)
(8.) Deaths by lightning in England and Wales in each
of the years 1877, 1878. (Extract from Eegistrar-General's
Eeport.)
40
LIGHTNING.
Division.
District.
Date of
Death.
Sex.
Occupation.
1
*3
2
3
4
6
Hartley Wintney .
"Woodstock . . .
Woodbridge . .
Atherstone .
1877.
26 Nov.
16 Aug.
29 Mar.
9 May
Male .
Male .
Male .
Male
TOTAL ....
Agricultural Labourer
Agricultural Labourer
Agricultural Labourer
Labourer
12
1
1
1
1
7
8
9
9
Chapel-en-le-Frith
Bolton ....
Skipton ....
Huddersfield
7 July
5 July
1 6 May
8 Auir
Male ,
Male .
Male .
Male .
Agricultural Labourer
Coal Miner ....
Hawker
Joiner
1
1
1
1
9
9
10
11
1
2
Sheffield ....
Aysgarth . . .
Houghton - le -
Spring. . . .
Bangor . ...
Woolwich . . .
Croydon ....
7 July
15 Oct.
16 Aug.
10 May
1878.
29 Aug.
1 3 Aug.
Female
Male .
Female
Male .
Female
Male .
Wife of Coal Miner .
Agricultural Labourer
Widow of Coal Miner
Quarry Labourer . .
TOTAL ....
Wife of Gardener . .
1
1
1
1
24
1
2
2
2
2
4
4
,5
Dartford. . . .
Blean
East Grinstead. .
Abingdon . . .
Braintree . . .
Depwade. . . .
Liskeard ....
24 Aug.
31 Aug.
23 July
23 Aug.
12 Aug.
12 Aug.
3 Aug.
Female
Male .
Male .
Male .
Male .
Female
Male .
Wife, Bricklayer's Lab.
Labourer
Labourer . ...
Bricklayer ....
Agricultural Labourer
Wife, Agric. Labourer
Farmer ...
1
fi
Cheltenham .
10 Aug.
Male .
Carter
1
6
6
Newcastle - under -
Lyme ....
24 July
31 Aug.
Female
Male .
Wife of Chair Mender
1
2
6
Atherstone .
6 Aug.
Male .
Miner ... .
I
7
8
Bourn ....
Runcorn ....
30 Aug.
6 Aug.
Male .
Male .
Son, Agric. Labourer .
Gardener
1
1
8
8
8
9
9
9
10
11
Northwich . . .
Ormskirk . . .
Burnley ....
Skirlaugh
Scarborough . .
Thirsk ....
Darlington . . .
Cardigan
24 July
27 June
7 Aug.
14 May
30 Aug.
16 Aug.
20 Mar.
20 July
Male .
Male .
Male .
Male .
Male .
Male .
Male .
Male .
Agricultural Labourer
Son of Farmer .
Son of Labourer
Son of Farmer .
Accountant .
Son of Farmer .
Shoemaker ....
1
1
1
1
I
1
1
1
(Reg. Eng.}
NOTES ON LIGHTNING. 41
I. G9, 10.
(9.) Deaths by lightning registered in Ireland in each
of the years 1877, 1878. (Extract from Registrar-General's
Report. )
Divi-
sion.
Superintendent
Registrar's Dis-
trict.
Date of
Death.
Sex.
Occupation.
j All Ages. [
1877.
TOTAL ....
7
II
S t r ibcin 6
21 June
Male
Labourer . .
1
IL
Millford .' .'
5 June
Female
Farmer's Widow . .
1
III.
V.
Bailieborough
Tullamore .
20 June
20 June
Female
Male .
Labourer's Daughter .
Tobacco Labourer . .
1
1
VI.
Swineford .
19 June
Male .
Son of Landholder .
1
VI.
Swineford .
19 June
Female
Daughter of Landholder
1
VIII.
Tralee . .
14 Sept.
Female
Child of Labourer . .
1
1878.
TOTAL ....
6
II.
Manorhamilton
13 April
Male .
Farmer's Son . . .
1
III.
Ardee . .
1 6 April
Male .
Farmer's Son . . .
1
VI.
Oughterard .
23 July
Male .
Landholder ....
1
VII.
Du.' t f^cjxvHii
27 June
Male
Farmer
1
VITT
D U.HH13/I1 wBi v
21 July
Male
Labourer ....
1
V 1-L-L*
VIII.
Rathkeale .
23 July
Male !
Farmer's Son . . .
1
(Reg. Ire.}
(10.) Deaths by lightning in England and Wales in the
8 years, 1871 78. (Extract from Eegistrar-General's
Report.)
Total in
1871.
1872.
1873.
1874.
1875.
1876.
1877.
1878.
the eight
Years,
1871-78.
ENGLAND .
28
46
21
25
17
19
12
24
192
Division I.
1
1
4
1
~
1
8
II.
"d
2
3
3
1
*2
5
22
III.
6
9
1
2
1
1
21
IV.
1
3
1
1
2
2
11
V.
1
2
2
5
1
11
VI.
2
5
4
'3
3
5
23
VII.
6
5
2
4
1
'l
1
21
VIII.
4
3
4
3
2
5
4
26
IX.
2
7
2
3
2
3
23
X
1
5
3
2
2
1
1
15
XL
4
1
1
3
1
1
11
(Reg. Eng.]
42 LIGHTNING.
I. Gil.
(11.) Table showing geographical distribution of fatal
thunderbolts in England and Wales, 1861 1878.
1
i
off
.1.
f
Order of prece-
dence qua visi-
a
c
gd
tation by fatal
s
s
PS
thunderbolts.
j
Counties included.
CO
1
te in 8 yea
i millions
teinlOye
i millions
g to the
of cases in
187178.
ion to the
n in the
8fil 78.
.a
$
S3
;S 6 2
llrf
1
m
1
r
Y
m
III
! Leicester, Rutland, Lin- \
VII.
coin, Nottingham, and >
21
18-05
19-29
5th
1st
Derby J
( Middlesex (extra Metro- "
III.
politan), Hertford,
} Buckingham, Oxford, i
(Northampton, Hunt-
21
17-45
8-03
5th
2nd
ingdon, Bedford, and
Cambridge . . . . j
IV.
( Essex, Suffolk, and Nor- }
11
11-01
13-55
8th
3rd
1 folk . J
IX.
Yorkshire
23
11-25
9 97
2nd
4th
! Durham, Northumber- j
X.
land, Cumberland, and >
Westmoreland . . . )
15
12-26
5-46
7th
5th
/ Gloucester, Hereford, \
VI.
\ Shropshire, Stafford, /
j Worcester, and War- I
23
10-15
7-35
2nd
6th
\ wick /
/ Surrey (extra Metropo-
II.
\ litan), Kent (extra
1 Metropolitan), Sussex,
22
11-94
4-48
4th
7th
\ Hants, and Berks . .
XL
Wales and Monmouth .
11
9-34
6-62
8th
8th
VIII.
Cheshire and Lancashire
26
9-09
4-11
1st
9th
{Wilts, Dorset, Devon,
V.
Cornwall, and Somer-
11
7-24
3-23
8th
10th
set .
I.
( London(includingMetro- \
\ politan District) . . }
8
2-92
33
llth
llth
For England and Wales . . .
192
10-09
6-50
(Compiled fro /n Rtg. Eny.)
NOTES ON LIGHTNING. 43
I. G12 18.
(12.) In the Government report of 1852, the average
number of persons in France stated to be annually killed
by lightning is 69. This is probably below the truth.
(Ar. 134.)
(13.) The following is an imperfect list, culled by Arago
from newspapers, of persons killed in a small portion of
France :
Year.
Months.
Numbers
of
killed.
Remarks.
1841
May October
12
1 on banks of Seine.
1842
May September
15
( 4 in a boat at Marseilles,
{ 3 under trees, 1 in a bed.
1843
April September
16
| 7 under trees, 3 under
\ a corn-rick.
1844
March October .
21
( 1 under tree, 2 ringing
1 bells.
1845
May October
11
( 3 under trees, 1 ringing
\ bells.
1846
May September
18
/ 3 under trees, 1 ringing
I bells.
1848
July August
4
1849
March May . .
8
2 under trees.
(Do. 135.)
(14.) In France, in the 17 years from 1835 to 1852,
1,308 persons were killed. (Mann, 1875, 540.)
(15.) In the United States, in 1797, from June to
August inclusive, 24 persons were struck, of whom 17
were killed. (Kaem. 351.)
(16.) In Prussia, 1,004 persons were killed during the
9 years from 1869 to 1877. (And. 170.)
(17.) In Austria, during the 8 years from 1870 to 1877,
1,702 fires were occasioned by lightning. (Do. 174.)
(18.) In Switzerland, 33 deaths occurred from light-
ning in the two years 1876 77. (Do. 175.)
44 LIGHTNING.
I. G19 30.
(19.) In Sweden, during the 60 years from 1816 to 1877,
664 persons were killed, of whom 15 were in towns, and
649 in the country. (Do. 172.)
(20.) In Russia (except Poland and Finland) in the 5
years, 1870 74, 2,270 persons were killed by lightning, of
whom 109 were in towns, and 2,161 in the country. (Do.
171.)
(21.) During these 5 years, the following fires were
occasioned in Russia (except Poland and Finland) by
lightning, viz. in towns 93, in the country 4,099. (Do.
171.)
(22.) The year 1880 appears to have been one of general
terrestrial electrical disturbance in Europe ; thunderstorms
were frequent; earthquakes and volcanic eruptions oc-
curred ; and auroree, earth currents, and waterspouts were
manifested. Earthquakes also occurred during this year
in Smyrna, in the Philippine Isles, and in Chili.
(23.) In Lima, and in Lower Peru generally, there are
no clouds, and no thunder and lightning, but a permanent
opaque vaporous fog. (Ar. 109.)
(24.) No rain falls in lower regions of Peru, and a S.W.
wind prevails. (Enc. Met. 111.)
(25.) Beyond 75 lat. thunderstorms are unknown in
the open sea. (Ar. 110.)
(26.) In Iceland, they are very little known. (Do. 111.)
(27.) In St. Helena, they are very little known. (Do.
123.)
(28.) It appears that there are frequently slight shocks
of earthquake in the valley of the Cabul river, in the
Punjab and Afghanistan ; but never thunderstorms.
(29.) In Jamaica, from November to April, lightning
and thunder are of almost daily occurrence at the summits
of the Port Royal Mountains. (Ar. 115.)
(30.) In Devonshire, Cornwall, and the neighbourhood
of Swansea, thunderstorms are frequent in proportion to
the absence of metallic mines, a fact probably due to their
furnaces and tall chimneys. (Do. 116.)
NOTES ON LIGHTNING. 45
I. G31 39.
(31.) In America there is an opinion that barns full of
grain or forage are more often struck than other buildings.
(Do. 199.)
(32.) Thunderstorms disperse, or turn off, at Niort,
Mayenne, France, where much diorite containing iron
exists. (Do. 117.)
(33.) At Grondome, in the Apennines, there is a pointed
eminence containing iron in serpentine rock, where frequent
short thunderstorms occur. (Do.)
(34.) In New Granada, the position of Tumba Barreto,
near the gold mine of Vega de Sapia, is avoided by the
miners, many having been killed there by the frequent
strokes of lightning. (Do. 180.)
(35.) "In the interior of the great towns of Europe, men
appear to be very little exposed to danger from lightning."
Do. 178.)
(36.) " According to an opinion widely prevailing,
arsons are much more exposed in villages and in the open
country." (Do. 180.)
(37.) In the Mediterranean, in 15 months of the years
182930, 5 of H.M. ships were struck. (Ar. 186.)
(38.) Table of frequency of thunderstorms.
Place.
No. of
years
obser-
Years in which
observed.
Mean No.
of days
vations.
per year.
Paris
41
1785 to 1837
13-6
London .
13
1807 1822
8-3
Berlin .
15
| 1770 1785
18-3
St. Petersburg
11
1726 1736
9-1
Toulouse
7
1784 1790
15-4
Padua .
4
1780 1783
17-3
Cairo
2
1835 1836
3-5
Rio Janeiro
6
1782 1787
50-6
Pekin . . .
6
1757 1762
5-8
(Do. 128.)
(39.) Thunderstorms are more numerous in Schleswig-
Holstein than in any other part of Central and Northern
46 LIGHTNING.
I. GUO 42.
Europe. The province is intersected by rivers and canals.
(And. 222.)
(40.) On August 9th, 1863, Mr. E. Whymper, in at-
tempting to ascend the Matterhorn, experienced, near its
summit, a severe snowstorm which lasted 26 Hours, and
shortly after its commencement became a heavy thunder-
storm, with much thunder and lightning all round his
position. All this time fine weather prevailed below the
mountain, only a small cloud having been observed near
its summit. ( Whymp. 169.)
(41.) On July 30th, 1869, Mr. E. B. Heathcote, of Ching-
ford, Essex, was with 3 guides within 500 feet of the top
of the Matterhorn, when he was surrounded by mist and
heard close to him much thunder. There was no wind nor
rain at the time, nor apparently did he see any lightning.
The Matterhorn, like all Alpine rock summits, is frequently
struck by lightning. (Whymp. 414.)
(42.) On the 15th July, 1880, at 1.30 a.m., an explosion
occurred at the Eisca coal pits near Newport, Monmouth-
shire, ' ' while a tremendous thunderstorm was raging over
the district." The shaft is 280 yards deep to the landing
place. The men at the time in the mine, numbering 119,
were killed, and the engine house, fan, and adjacent shaft
were greatly damaged. " Yery vivid and frequent light-
ning was observed." The cause of the explosion has not
been ascertained, but it was conjectured at the time that
' ' the electrical condition of the atmosphere above ground
may have had something to do with it." (Stand. 16/7/80.
Graph. 24/7/80.)
NOTES ON LIGHTNING ENGINEERING. 47
II. A 1-6.
i- DIVERSITY
CHAPTER II. NOTES ON LIGHTNING
ENGINEERING.
(A.) HISTORICAL NOTES.
(1.) " MANY centuries before Christ it had been observed
that yellow amber (electron), when rubbed, possessed the
power of attracting light bodies This is the germ
out of which has grown the science of electricity, a name
derived from the substance in which this power of attraction
was first observed. This attraction was the sum of the
world's knowledge of electricity for more than 2,000
years." (Tynd. 1.)
(2.) In A.D. 1600, Dr. Gilbert observed that various
spars, gems, stones, glasses, and resins, possessed the
same power as amber. (Do. 2.) \_Seealso I. C. 63.]
(3.) In 1675, Robert Boyle observed that rubbed amber
became itself attracted. He also saw the light of elec-
tricity by rubbing a diamond. (Do.)
(4.) About 1675, Otto von Guericke, Burgomaster of
Magdeburg, and inventor of the air-pump, devised the
electrical machine in the form of a ball of sulphur. He
also noticed the power of repulsion. (Do.)
(5.) In 1675, electric light was first observed by Pickard,
and in 1705, John Bernouilli and Hawksbee experimented
on it. (Do.)
(6.) In 1708, Dr. "Ward experimented with amber and
wool, and produced cracklings and light ; and he says,
" This light and crackling seem in some degree to repre-
sent thunder and lightning." This is the first published
allusion to thunder and lightning in connection with elec-
tricity. (Do. 3.)
48 LIGHTNING.
II. A 7 13.
(7.) In 1729, Stephen Gray also observed the electric
spark, and that the power evolved seemed to be of the
same nature with that of thunder and lightning. In the
same year he first noticed the actions of conduction and
insulation. (Do. 13 and 14.)
(8.) In 1733 37, the influence of moisture as a conduc-
tor was first demonstrated by Du -Fay, who sent a charge
through 1,256 feet of pack-thread. He also discovered
that there are two kinds of electricity, vitreous and
resinous. (Do. 22.)
(9.) On the 23rd January, 1744, Ludolf, at the opening
of the Academy of Sciences at Berlin by Frederick the
Great, first ignited substances by the electric spark. (Do.
80.)
(10.) On the 4th November, 1745, Kleist, a clergyman
of Cammin, in Pomerania, announced by letter to Dr.
Lieberkiihn, of Berlin, the discovery of the principle of the
Leyden jar. Kleist missed the explanation of the prin-
ciple, but the Leyden philosophers gave it, whence it
derived the name of " Leyden jar." (Do. 66.)
(11.) In 1748, Dr. Watson and Dr. Bevis improved the
apparatus so as to arrive at the form of the present day.
(Do.)
(12.) Benjamin Franklin was born at Boston in January,
1706. He was a printer by trade, and kept a general store
at Philadelphia for some time. He first heard of electri-
city at a lecture by Dr. Spence in 1746. He then inves-
tigated the subject and made experiments himself , sending
accounts of them to the Royal Society. In 1750 he
reported on the identity of electricity and lightning, and
submitted the idea of fixing sharp pointed iron rods to the
summits of buildings in order to protect them from light-
ning. Buffon, the great naturalist, had Franklin's
pamphlet on the subject translated, and through this
means it spread over Europe. (And. 18.)
(13.) At Buffon's instigation, M. D'Alibard made ex-
periments, according to Franklin's suggestions, with a
NOTES ON LIGHTNING ENGINEERING. 49
II. A 1419.
pointed iron rod 1 inch in diameter and 80 feet long, at
Marly, near Paris; and on the 10th May, 1752, during a
thunderstorm, the custodian of the rod (during D'Alibard's
absence) observed at it vivid flashes. (Do. 20.)
(14.) Unconscious of D'Alibard's success, Franklin
himself experimented with a kite having a thin iron wire
1 foot long at the top, and on the evening of the 4th July,
1752, during a thunderstorm, he drew flashes with this
kite in a field near his house at Philadelphia. (Do.
23.)
(15.) In 1752, Franklin erected an iron lightning rod at
his house, with a sharp steel point projecting 7 or 8 feet
above the roof, and with the other end 5 feet in the ground
By means of a contrivance, two bells were rung whenever
an electrical current passed through the rod. He found
that the bells rang sometimes "when there was no light-
ning or thunder, but only a dark cloud over the rod;"
sometimes, after a flash of lightning they would suddenly
stop ; and at other times, when they had not rung before,
they would suddenly begin to ring ; and there were con-
siderable fluctuations in the currents. (Do. 26.)
(16.) Franklin advertised, recommending people to erect
their own iron rods, and giving simple directions ; houses
thus armed were, however, found to be struck by lightning
owing to the rods having been put up wrongly, or by im-
postor professors. (Do. 29.)
(17.) "The untaught multitude and the bigoted zealots
opposed in Europe, as they did in America, the establish-
ment of lightning conductors." To these was added "a not
numerous but powerful section of literary men," chiefly
French. The Abbe Nollet (teacher in Natural Philosophy)
considerably retarded the introduction of lightning rods.
(Do. 35 and 18.)
(18.) Mr. Wilson, against the opinion of Franklin,
Cavendish, and Watson, advocated the use of blunt con-
ductors. (Tynd. 101.)
(19.) Franklin devised the theory of a single electric
P
50 LIGHTNING.
II. A 20 28.
fluid to explain electrical phenomena. Symmer devised
that of two fluids, which is simpler. (Do. 22.)
(20.) The inscription on a medal dedicated to Franklin
after the declaration of American Independence was
JSripuit fulmen ccelo, sceptrumque tyrannis. (HerscTi.)
(21.) In 1753, Professor Eichmann was killed at St.
Petersburg by "a thundercloud which discharged itself
against the external rod " of his apparatus. (Tynd. 101.)
[See III. 38.]
(22.) In 1757, Be Romas, at Nerac, in France, sent up
a kite 400 or 500 feet into the air during a moderate storm,
and obtained thirty flashes, 9 or 10 feet long and 1 inch
broad, in less than an hour, besides a thousand of 7 feet
long and under. (Ar. 234 and Hersch.}
(23.) About 1772, Beccaria experimented, during
thunderstorms, at Yalentino Palace, Turin, with rods whose
lower portions, connected with the ground, were slightly
separated from the pointed upper parts, and obtained
vivid sparks across the gap. (Ar. 230.)
(24.) The destruction of the steeple of St. Bride's Church
in London on the 18th June, 1764, led Dr. Watson to force
the claims of rods on public attention in England. He
erected the first rod in England at his own cottage at
Payneshill, near London, in 1762. (And. 38.) [See III.
62.]
(25.) The first lightning rod placed on a public building
in Europe was at St. Jacob's Church, Hamburg, in 1769.
(Do. 43.)
(26.) In 1769, St. Paul's Cathedral was protected by
lightning rods. (Tynd. 102.) [See III. 145.]
(27.) The fact of Purfleet storehouse, when defended by
a rod, being struck and damaged on the 15th May, 1777,
led to an outcry against pointed rods. (And. 41.) [See
III. 39.]
(28.) In 1779, Lord Mahon (afterwards Lord Stanhope)
published his " Principles of Electricity," with an explana-
tion of " returning strokes." (Tynd. 102.)
NOTES ON LIGHTNING ENGINEERING. 51
II. A 2935.
(29.) In 1829, solid iron rods 1 in. diameter, with tops
of copper tipped with gold, were ordered to be used for the
War Department powder magazines. (A. M., W. 0. 1829.)
(30.) " The most decisive evidence in favour of conduc-
tors was obtained from ships." Sir William Snow Harris's
fixed lightning rods for ships were of great value. (Tynd.
102.)
(31.) In 1820, Sir W. Snow Harris turned his attention
to the best means of protecting H.M. ships from damage
by lightning. In 1839, a Government Commission was ap-
pointed, and on their report Harris's system was adopted.
In 1855, he designed a system of protection for the new
Houses of Parliament at a cost of 2,314, consisting
mainly of copper tubes and bands. In 1858, he was called
upon by the War Office to give advice as regards protect-
ing powder magazines, and his recommendations were
adopted. (And. 85 98.)
(32.) In 1822, the French Minister of the Interior
ordered all public buildings to be protected by rods, and
applied to the Academy for advice ; this body nominated a
Committee, who, through M. Gay Lussac, one of their
number, presented a report, dated 23rd April, 1823, which
laid down rules for guidance as to the area over which
rods possessed a protective power. (Do. 76.)
(33.) " When thirty years had passed, the instances of
buildings " armed with conductors " being struck became
so numerous that it was impossible to ignore them any
longer, and another Committee of the Academy was
selected ; their report was made on the 1 8th December,
1854, and was drawn up by Professor Pouillet. (Do. 78.)
(34.) On account of the Palace of the Louvre having
been struck, though armed with rods, a third Committee
of the French Academy assembled, and presented (again
through Professor Pouillet) a report dated 19th February,
1855. (Do. 81.)
(35.) Twelve years afterwards, several powder maga-
zines with rods on them having been struck, a fourth
D2
52 LIGHTNING.
II. B 18.
Committee of the Academy was nominated. Marshal
Vaillant, Minister of War, and M. Becquerel, were
members of it. Professor Pouillet was again the author
of their report, which was dated 14th January, 1867. (Do.
82.)
(B.) DETAILS OF LIGHTNING EODS.
(1.) The disadvantages of rigid bars are now (1855)
avoided by the use of flexible metal cords. (Ar. 247.)
(2.) According to facts collected, square or cylindrical
bars of iron T 8 <j inch in diameter are sufficient to prevent
fusion. (Do.)
(3.) Abrupt changes of course in rods should be avoided.
(Do. 250.)
(4.) A rod of copper % inch in diameter, and 6 inches
long, has never been fairly melted ; and much less dimen-
sions have carried away heavy discharges. (Harr. 113.)
(5.) Harris's practical deductions regarding rods were :
(a.) Copper was the best metal to use.
(b.) It should be not less than inch in diameter.
(0.) The principal detached metallic masses of the build-
ing should be connected to it.
(d.) The rods should be attached to the most prominent
points.
(e.) They should be carried close to the walls and directly
into the ground. (Do. 123.)
(6.) Ships' conductors were at first iron chains, or long
links of small iron rods, carried from the head of the mast
over the side of the ship into the sea. (Do. 130.)
(7.) In 1762, at Dr. Watson's suggestions, H.M. ships
were supplied with rods formed of long links of copper rod
inch in diameter, united by small eyes, and carried from
the top-gallant mast head into the sea as before. (Do.
131.)
(8.) It was found that linked and chain rods were bad,
NOTES ON LIGHTNING ENGINEERING. 53
II. B 918.
as the links were often broken and the metal fused. (Do.
133.)
(9.) In 1824, the French used wire rope conductors for
their ships. (Do. 134.)
(10.) All these conductors, being parts of the rigging,
were found to be dangerous. Seamen came unawares into
their bights when the top-gallant masts were struck, &c.,
and thus formed portions of the lines of least resistance for
the discharge. Besides, being movable and generally
stowed away till thunder weather approached, the rods
were not always found when wanted, nor applied in time,
nor properly. (Do. 137.)
(11.) In 1821, Sir W. Snow Harris proposed to incor-
porate the rods in the masts of the ship, thus practically
making them fixed, and to connect them with the metals
of the hull, and finally with the sea by means of the keel
and kelson bolts. (Do. 141.)
(12.) His rods were bands of copper T L to | inch thick,
and 1^ to 5 inches wide, let into the masts. (Do. 142.)
(13.) This system was, about 1831, adopted into the
British Navy, and it proved very successful in reducing the
number of accidents to ships from lightning. (Do. 148.)
(14.) A similar system was proposed for merchant ships,
except that from the heads of the lower masts, wire ropes,
^ inch in diameter, were let down the rigging, and over
the ship's side into the sea. (Do. 151.)
(15.) The French employ for buildings copper ropes T 4 <y
to T % of an inch in diameter for each 82 feet in height.
(Mann, 1875, 534.)
(16.) " Conductors require to be of larger size in pro-
portion to their length." (Do.)
(17.) Dr. Mann recommends " a rope of galvanised iron,
consisting of 42 strands of iV-inch wire with a brush
point." (Do.)
(18.) " Conductors require to be expanded and ampli-
fied both at their summits and at their roots or base."
(Do. 533.)
54 LIGHTNING.
II. B 1929.
(19.) The French electricians recommend a cluster of
points instead of one alone. (Do. 536.)
(20.) "What the dimensions in a lightning conductor
are that would fulfil this essential condition of giving
sufficient capacity for the safe transmission of the largest
possible discharge, is yet an unsettled question." (Do. 533.)
(21.) M. Melsen aims at covering a building with a sort
of metallic net, with numerous points and earth contacts.
At the Hotel de Yille at Brussels his system has been
adopted. This building has a pinnacled spire 297 feet
high. The main conductors are 8 galvanised iron rods,
each about f inch in diameter and 310 feet long. These
in their course gather up strands of similar size from the
ridges, parapets, turrets, and gables. (Do.)
(22.) M. Melsen's experiments tend to show that copper
is less strong than iron to resist the disintegrating effects
of a powerful discharge. (Do. 1878, 334.)
(23.) A copper rope should not be less than ^ inch, and
a galvanised iron one not less than T 8 ^ inch in diameter.
(Do. 335.)
(24.) Conductors should have no joints except well-
soldered ones. (Do. 346.)
(25.) Chains and linked rods should be strenuously
avoided. (Do.)
(26.) The straighter conductors are the better, lest
branch circuits should be determined. (Do.)
(27.) " A wire equivalent to the ordinary galvanised iron
wire known as No. 4, which is inch in diameter, and used
so largely for telegraphic purposes, is amply sufficient for
any dwelling-house." (Preece, 344.)
(28.) The above opinion is based on experience, derived
from the immunity from injury by lightning obtained by
telegraph poles supplied with No. 8 earth wires (which are
only half as massive), whose upper extremities terminate
in points. (Do. )
(29.) Mr. Preece "can conceive no case in which % inch
stranded galvanised iron wire is not ample." (Do. 346.)
NOTES ON LIGHTNING ENGINEERING. 55
II. B30 40.
(30.) Mr. Latimer Clark agreed with. Mr. Preece as to
the use of No. 4 galvanised iron wire for ordinary houses
where economy had to be studied. (Lett. Clark, S. T. E.
373.)
(31.) Copper is the best material for rods. (W. 0. 1875,
11.)
(32.) Iron may be employed, but larger dimensions must
be used, so as to give the same conductivity as copper.
(Do. 12.)
(33.) Copper conductors should be as follows: rods
inch diameter, tubes | inch diameter and J- inch thick,
bands 1 inches wide and J- inch thick. (Do. 13.)
(34.) Iron conductors should be solid rods 1 inch in
diameter, or bands 2 inches wide and | inch thick. (Do.
14.)
(35.) Copper is, as regards iron, more conductive, less
corrodible, more expensive, more liable to mechanical
injury, more liable to be stolen, and more fusible. (Do. 15.)
(36.) Roughly speaking, copper and iron cost the same
for the same conductivity. (Do. 16.)
(37.) The expansion and contraction of the metal must
be provided for, especially at the joints. (Do. 17.)
(38.) Where contact of two different metals occurs,
precautions should be taken to prevent access of moisture,
and hence galvanic action and decomposition. (Do. 25.)
(39.) Ample surface is essential to rods in order to give
the discharge free room for expansion. (Do. 1858, App.
A 10
(40.) Details of conductors affixed to Weedon powder
magazines in 1857, under the personal^direction of Sir W.
Snow Harris, are given as aids in forming specifications
and estimates, viz. :
Solid copper pointed rods, % inch diameter, 5 feet high,
Flat ridge conductors, 4 inches by % inch.
Tubular gable conductors, 1 inch by inch.
Flat vertical conductor, 3 inches by inch.
56 LIGHTNING.
II. B41 46.
Copper rain-water down-pipes.
Underground copper earth connections, 3 inches by
$ inch, and 4 feet long to forks or branches.
Copper forks of earth connections, each 2 inches by
inch and 4 feet long.
Flat copper bands, from copper sheathing on doors to
rain-water pipes, 2 inches by ty inch. (W. 0. 1858, and
R. E. A. 89.)
(41.) As a general rule all the joints should be covered
with a layer of solder at least 1 inch thick. (Franc.
Mich. Tel. 64.)
(42.) "Copper, much less resisting than iron in a me-
chanical point of view, undergoes with rapidity, under the
influence of electric currents and atmospheric variations,
both a kind of disaggregation and temper, rendering it
fragile and brittle, i.e. in a very short time its primitive
solidity is much altered." (Do.}
(43.) There are two principal parts in a lightning rod,
the terminal rod and the stalk; the terminal rod is a
pointed bar of iron from 6 to 10 feet high, fixed verti-
cally to the roof of the edifice to be protected ; and its
basal section is about 2 of 3 inches in diameter. (Gan.
833.)
(44.) The stalk is best formed of wire cord of half a
square inch in section, as being less rigid. Copper wire
cord is recommended by the French Academy of Sciences.
(Do.)
(45.) The conditions for lightning rods are :
(a) So large as not to be melted.
(b) To terminate in a point.
(<?) To be continuous, and to have intimate connec-
tion with the ground.
(d) The metallic surfaces of the building to be con-
nected to it. (Do.)
(46.) "If the last two conditions are not fulfilled there
NOTES ON LIGHTNING ENGINEERING. 57
II. B47 55.
is great danger of lateral discharges ; that is to say, that
the discharge takes place between the conductor and the
edifice, and then it only increases the danger." (Do. 834.)
(47.) " The first conductors were invariably rods of iron,
this metal being preferred by Franklin and his immediate
followers as cheap, ready at hand, and answering all pur-
poses in practice." (And. 50.)
(48. ) The French Committee of the 1 8th December, 1 854,
recommended greater capacity for rods and as few joints
as possible, and all joints to be tin soldered. (Do. 79.)
(49.) Brass is not so good a conductor as copper; it is
also very liable to destruction by atmospheric influences ;
and it was discarded altogether some thirty or forty years
ago. (Do. 107.)
(50.) The cost of copper is seldom less than six or seven
times that of iron. (Do. 108.)
(51.) Till recently it was very difficult to manufacture
long rods or bands of pure copper. The Spanish " Bio
Tinto " copper is barely equal to iron in conductivity. The
difficulty of obtaining pure copper was solved by the de-
mand for submarine cables. (Do. 110.)
(52.) The lightning rods made at the works of Mr. E. S.
Newall, F.R.S., at Gateshead-on-Tyne, established forty
years ago, have generally a conductivity of 93 per cent, of
pure copper. (Do.)
(53.) M. Melsen prefers iron to copper, since it has more
molecular strength and would resist a great charge better.
(Do. 117.)
(54.) The Victoria and Clock Towers of the Houses of
Parliament, each three hundred feet high, have copper
bands 5 inches wide and inch thick, connected with the
roof metal, and with a metallic staircase in each tower.
The roofs of Westminster Palace are covered with galva-
nised iron, and, in many cases, connected to the earth by
cast-iron water-pipes. (Do. 119.)
(55.) In France lengths of iron bars are principally used
as lightning rods. The whole rod is covered with tar or
D3
58 LIGHTNING.
II. B56 60.
paint, except the terminal, in order to preserve it from the
air. Sometimes galvanised iron cables of 1 inch diameter,
or red copper cables of inch diameter are used. (Do.
129 and 132.)
(56.) In France " all masses of metal used in the con-
struction of the building are metallically connected with
the paratonnerres. As a rule this is done by pieces of iron
about inch square, which are strongly soldered to the
metal surfaces, and then connected with some part of the
conductor or ridge circuit." (Do. 130.)
(57.) In America the conductors are of iron. (Do. 134.)
(58.) "After repeated experiments, Mr. B. S. Newall
has arrived at the conclusion that a conductor made of
copper of adequate size is the best, and, in the end, the
cheapest means of protecting buildings from the effects of
lightning." (Do. 143.)
(59.) " For private houses and buildings, a rope made
of copper ought to be at least J- inch in diameter. For
chimneys of manufactories where gases are liable to corrode
the rope, it had better be a little thicker." (Do. 151.)
(60.) In June and July, 1880, Mr. W. H. Preece, with
Dr. Warren de la Eue's battery of 3,240 chloride of silver
cells (whose charge was accumulated in a condenser of a
capacity of 42 -8 microfarads, whereby a potential of 3,317
volts was obtained), transmitted currents through copper
conductors (and afterwards through leaden ones) of pre-
cisely the same mass, but in three different forms, viz. those
of a solid cylinder, a tube, and a ribbon. The currents
passed through platinum wire of -0125 inch diameter, of
various lengths, which were calculated to display by the
character of their deflagration, or by the shades of heat
manifested, any difference (not less than 5 per cent.) that
might have existed in the strength of the discharges due
to the difference in the forms of the conductors. No dif-
ference was apparent in any of the currents ; and the con-
clusion arrived at by Mr. Preece was " that the discharges
of electricity of high potentials obey the law of Ohm, and
NOTES ON LIGHTNING ENGINEERING. 59
II. 0111.
are not affected by change of form. Hence, extent of sur-
face does not favour lightning discharge. No more efficient
lightning conductor than a cylindrical rod or a wire rope
can therefore be devised." (Tel. 1st September, 1880,
Paper read by Mr. Preece before British Association.)
(C.) POINTS OF HODS.
(1.) Franklin only required the tops of rods to rise a
little above the tops of the chimneys. (Ar. 240.)
(2.) Cavendish, Priestley, and other English physicists
fixed the height of the rod above the house at 10 feet.
(Ho.)
(3.) " In France (1855) our builders go up to 10 metres
(32 feet 6 inches), and even only stop there on account of
considerations connected with solidity." (-Do.)
(4.) In 1790 the Philosophical Society of Philadelphia
approved of Mr. R. Patterson's plan of making points of
plumbago. (Do. 244.)
(5.) In France (1855) a single point is always used.
(Do.)
(6.) In Germany and England (1855) sometimes a single
point, and sometimes a brush of points, is used. (-Do.)
(7.) One reason alleged for the brush point was, that if
all the points became blunt, their combined action would
still equal that of a good single point. (Do.)
(8.) Another was, that on account of their divergency,
one or other of them would always present itself more or
less directly to an approaching thunderstorm. (Do.)
(9.) Arago preferred himself the single point, as recom-
mended by Franklin. (Do. 245.)
(10.) Points were gilded because, being of iron, they
soon became rusted ; but this not being found durable,
copper gilt points were screwed on ; and lastly, platinum
points were used. (Do. 243.)
(11.) Discharges " occasionally become so modified by
60 LIGHTNING.
II. 01219.
various circumstances as to assume a mere progressive and
quiet form often free from any attendant danger what-
ever. If a pointed metallic rod project from one of the
terminating planes of a charged system into the inter-
vening dielectric, the consequence frequently is a luminous
brush of beautifully coloured light. The discharge is pro-
gressive and occupies a sensible time." " (Harr. 18.)
(12.) " Any termination which can be conveniently given
to a conductor, if even it were a ball of 1 foot in diameter,
would be, in relation to perhaps 1,000 acres of cloud, vir-
tually a pointed conductor." (Do. 117.)
(13.) Glass balls were placed on the summits of the con-
ductors of some of the lighthouses in lieu of points, it
being considered that glass would repel the electric dis-
charge. (Do. 129.)
(14.) Franklin experimented on the power of points, and
inferred that pointed rods robbed thunderclouds of their
charge, and made them shrink back. (Do. 187.)
(15.) "The pointed termination of the conductor is a
matter of some practical importance, because it establishes
a slow and gentle discharge of an accumulation of electrical
force at high tension." (Mann, 1875, 535.)
(16.) In Paris the rods usually project 12 to 30 feet
above the buildings. (Do.}
(17.) Professor Gavarret has shown by experiments on
the function of points, that the tension which can be pro-
duced in a charged conductor, towards which a point is
directed, diminishes according as the point is made more
acute. (Do. )
(18.) Platinum points are specially made for conductors
in Paris. (Do.}
(19.) At the Hotel de Ville, Brussels (where the system of
protection is designed by M. Melsen), there are U 426 points
distributed in 60 aigrettes, and lying in 10 different places,
provided as air terminals." Of these, 385 are of copper,
63 of galvanised iron, and 8 are spikes gilded at the end.
(Mann, 1878, 330.)
NOTES ON LIGHTNING ENGINEERING. 61
II. 02032.
(20.) Tips of silver alloy are recommended for points.
(Do. 335.)
(21.) The larger the building, the more points should
be used. (Do.)
(22.) Terminals should branch out into several points or
aigrettes. (Do.)
(23.) Points should project into the air at least 8 feet.
(1*0
(24.) A projection of 3 feet beyond the chimney-top is
sufficient. The point can then be inspected. (Preece, 348.)
(25.) The principal function of a conductor depends on
its point. (Do.)
(26.) As regards the action of points on charge, Faraday
made an experiment demonstrating that when a charge
passed through the air, this action " simply converted the
line of discharge into a conductor ; it was precisely the
same as if a wire connected the two points." (Do, 378.)
(27.) The electric discharge is " simply due to the fact
of two points separated by air being raised to such a dif-
ference of potential that the resistance of the air cannot
restrain their neutralisation across it. Now if we prevent
the increase of potential by dissipating the charge as it
collects we effect this object. This is the function of
points." (Do. 353.)
(28.) " Points prevent the accumulation of charge. A
pointed body, such as a needle, directed towards a charged
conductor dissipates the charge at once. A pointed con-
ductor directed towards a charged cloud dissipates the charge
in its immediate neighbourhood quietly and silently." (Do.)
(29.) "Thus it is that the chief merit of a lightning
conductor consists in the action of its pointed end." (Do.)
(30.) " A properly constructed conductor may be said to
prevent electric discharge within the sphere of its action."
(Do.}
(31.) A glow or brush may be seen at the top of a
lightning rod if it is in good order. (Do.)
(32.) A fork or brush of three or four points may be
62 LIGHTNING.
II. C 3339.
used on the tops of rods when the rods are widely sepa-
rated, or on single prominent points. (W. 0. 1875, 34.)
(33.) Pointed terminations are so far useful that they
" tend to break the force of the discharge of lightning
when it falls on them." In fact, before the explosion
takes place, a large amount of the discharge which would
otherwise take part in the explosion runs off through the
points. (Do. 1858, App. A. 12.)
(34.) Gilding points is of no use. (Do.)
(35.) It is sufficient if the terminating rods are roughly
pointed. (Do.)
(36.) The use of brush points is recommended, since,
" radiating in all directions, they will hasten the neutralisa-
tion of the electrified cloud ; and in the event of a discharge,
the discharge, by dividing amongst them, will prevent
their fusion." (Franc. Mich. Tel. 44.)
(37.) " If you impart a good charge to a sphere, you
may figure the electric fluid as a little ocean encompassing
the sphere, and of the same depth everywhere. . . . But
supposing the conductor to be a cube, an elongated cylinder,
a cone, or a disc, the depth, or, as it is sometimes called,
the density, of the electricity, will not be everywhere the
same. The corners of the cube will impart a stronger charge
to your carrier than the sides. The end of the cylinder
will impart a stronger charge than its middle. The edge
of the disc will impart a stronger charge than its flat surface.
The apex or point of the cone will impart a stronger charge
than its curved surface or its base." (TynA. 51.)
(38.) Professor Eiess, of Berlin, found that he could
deduce with great accuracy the sharpness of a point from
the charge which it imparted. He compared in this way
the sharpness of various thorns with that of a fine English
sewing needle. (Do. 53.)
(39.) " Considering that each electricity is self -repulsive
and that it heaps itself upon a point in the manner here
shown, you will have little difficulty in conceiving that
when the charge of a conductor carrying a point is suffi-
NOTES ON LIGHTNING ENGINEERING. 63
II. 04046.
ciently strong, the electricity will finally disperse itself by
streaming from the point." (Do.)
(40.) " Flames and glowing embers act like points ; they
also rapidly discharge electricity." (Do. 58.)
(41.) The point is usually of platinum or gilt copper.
(Gan. 833.)
(42.) ' ' The action of a lightning conductor depending on
induction and the power of points, Franklin, as soon as he
had established the identity of lightning and electricity,
assumed that lightning conductors withdrew electricity
from the clouds ; the converse is the case." (Do.)
(43.) "When a stormcloud positively electrified, for
instance, rises in the atmosphere, it acts inductively on
the earth, repels the positive, and attracts the negative,
fluid, which accumulates in bodies placed on the surface
of the soil the more abundantly as these bodies are at
a greater height. The tension is then greatest on the
highest bodies, which are therefore most exposed to the
electrical discharge; but if these bodies are provided
with metallic points like the rods of conductors, the
negative fluid withdrawn from the soil by the influence
of the cloud flows into the atmosphere and neutralises the
positive fluid of the cloud." (Do.)
(44.) "Hence, not only does a lightning conductor tend
to prevent the accumulation of electricity on the surface of
the earth, but it also tends to restore the clouds to their
natural state, both which concur in preventing lightning
discharges." (Do.)
(45.) "The disengagement of electricity is, however,
sometimes so abundant that the lightning conductor is
inadequate to discharge the ground, and the lightning
strikes ; but the conductor receives the discharge in con-
sequence of its greater conductivity, and the edifice is
preserved." (Do.)
(46.) The French Committee, who reported through 1
Professor Pouillet on the 18th December, 1854, recom-
mended the points to be rather blunt, as sharp points ran
64 LIGHTNING.
II. 04755.
risks of becoming fused ; also that they should be of copper,
not of platinum, since the copper became less heated, was
a better conductor, and cheaper. (And. 79.)
(47.) The point in France is sometimes of platinum, but
generally of pure red copper, or an alloy of silver and
copper. (Do. 127.)
(48.) In America, the terminal rod generally projects
about 4 feet above the highest point of the building, and
consists of round iron. The upper end is not always
pointed. (Do. 134.)
(49.) Mr. Newall's terminal rods are from 3 to 5 feet
high, and from f to f inch in diameter. At the top they
form a brush of 4 points. (Do. 144.)
(50.) The German terminal rod or Aufgangstange is of
iron, and varies from 10 to 30 feet high, and has a single
point. (Do. 145.)
(51.) If a prominence on the earth electrified by a cloud
" be armed with a point connected with the earth, then, as
soon as the potential of the point is raised, even slightly,
the electricity passes off from the point into the air ; the
prominence can no more be highly electrified than a leaky
bucket can be filled with water." (Jen. 105.)
(52.) " The brush discharges, whether luminous or
otherwise, are due to the accumulation of electricity in
large quantities at points." (Do. 92.)
(53.) " The brushes or sparks which fly off from points
charged to high potential, show that in all apparatus
intended to remain charged at a high potential every angle
and point must be avoided on the external surfaces."
(Do. 105.)
(54.) " Fix a fine metal point to the conductor of the
electric machine and work the machine. It will be impos-
sible to collect any appreciable charge on the conductor ;
the electricity all escapes by the point." (Gord. I. 22.)
(55.) There is a very much greater force tending to
drive electricity from a point than from any other por-
tion of a conductor. (Do. 23.)
NOTES ON LIGHTNING ENGINEERING. 65
H. D 112.
(D.) EARTH CONNECTIONS OF EODS.
(1.) Mr. Hare, Professor of Chemistry in Philadelphia,
proposed underground iron water-pipes as the earth con-
nections of lightning rods. (Ar. 246.)
(2.) Mr. Eobert Patterson, in 1790, recommended placing
earth connections in a kind of well filled with charcoal or
embers. (Do. 247.)
(3.) It is a mistake to suppose that watertight cisterns
make good earths. (Do.}
(4.) If the soil is humid, the metal soon rusts, but well-
burned charcoal preserves the iron. (Do.)
(5.) Ordinary dry charcoal is found not to be a good
conductor of " fulminating matter." (Do. 254.)
(6.) " A faulty termination of the earth connection is of
all else the most common and frequent blunder in relation
to lightning conductors that is made." (Mann, 1875, 536.)
(7.) A moist earth contact is recommended. (Do.)
(8.) " All competent electrical engineers are now keenly
alive to the automatic electrolytic action that is apt to take
place in the earth contacts of a lightning conductor."
(Do. 537.)
(9.) "An earth contact of 1,000 square metres (1,196
square yards) has been fixed by the best French authorities
as sufficient for all practical purposes for a conductor of
copper that is 1 centimetre (1% inch) square." (Do.)
(10.) M. Callaud proposes to use with this 2 T 8 <j bushels
of broken coke. (Do.)
(11.) Occasionally a bore of 4 or 5 inches diameter, and
16 or 20 feet deep, into damp soil should be made for the
insertion of the earth connection. (Do. 538.)
(12.) At the Hotel de Yille, Brussels, the earths of the
lightning rods are as follows : At 3 feet from the ground
the rods enter a box of galvanised iron filled with zinc
poured in molten, out of which issue three bundles of
iron rods to form earth connections. One bundle is
carried beneath the pavement into a cast-iron cylinder,
66 LIGHTNING.
II. D13 22.
2 feet diameter and 8 feet long, sunk in a well hollowed
in the ground, and providing a water contact. A second
bundle is attached to the iron main of the gas service
of the town. The third is attached to the iron water
service of the town. The entire earth contact is about
330,000 square yards. (Do. 1878, 332.)
(13.) An earth contact of large extent is needed ; the best
is a gas or water main ; otherwise a trench in moist ground,
20 feet long, packed with gas coke, should be used. (Do. 335. )
(14.) Where the earth is dry the contact must be larger.
(Do.)
(15.) Conductors may be either connected with iron gas
or water mains, buried in coke, attached to metal in moist
earth, or carried down wells. (Preece, 347.)
(16.) At Jersey, the conductor of a church was found
broken off 2 feet from the ground, and it had been so for
years. (Do.)
(17.) At Lydney, the earth connection of the conductor
of the church consisted of an iron gas-pipe leaded into a
loose stone resting on a stone pavement. (Do.)
(18.) At Llandaff Cathedral, the conductor, a small
copper stranded wire, fixed by galvanised iron wall hooks,
was found corroded and eaten away, 1 foot below the
surface, by electrolytic action, the surfaces at breakage
clearly denoting the action of a current. (Do. 354.)
(19.) The potential of the atmosphere increases on
ascending. Thus there is a current between the rod at the
top of a spire and the earth. The result is electrolytic
action at the junction with the ground. (Do.)
(20.) This is mitigated by making earth with as large a
mass as possible. (Do.)
(21.) Conductors should invariably be continued through
" light dry soil, such as shingle and sand," to soil which
is permanently damp. (W. 0. 1875, 4.)
(22.) Good earth connections are most important. Con-
ductors should be led if possible into springs, wells of
water, or ground permanently wet. (Do. 38.)
NOTES ON LIGHTNING ENGINEERING. 67
II. D23 37.
(23.) The sea is a good earth, also any body of water
not en closed in a watertight tank. (Do.)
(24.) Shingle, dry sand, and vegetable mould are bad
earths. (Do.)
(25.) All large systems should have several earths, "so
that should one be defective, the discharge may be effected
through the other." (Do.)
(26.) Conductors should be led into moist ground by
trenches 18 inches below the surface. (Do. 39.)
(27.) Not less than 30 feet of metal should be in contact
with moist earth. (Do.)
(28.) A flow of water from the down-pipes of the roof
should be led if possible over the earths. (Do. 40.)
(29.) Special precautions are necessary in rocky and dry
soils. The trenches should extend 30 to 120 feet from the
foot of the conductor. (Do. 41.)
(30.) Earth connections in trenches may be of railway
or old iron. (Do. 42.)
(31.) The trenches should be filled with cinders, or with
coal ashes. (Do.)
(32.) Water-pipes make good earths, but not gas-pipes,
on account of their liability to be fused. (Do.)
(33.) In 1846, the War Office Eegulations prescribed
covered cisterns in preference to open trenches as being less
liable to evaporation, and the cisterns were ordered to be
kept full of water. (Do. 1846.)
(34.) Conductors should terminate below in damp or
porous soil. (Do. 1858, 8.)
(35.) If the soil is dry, radiating trenches should be cut
30 feet long and 18 inches or 2 feet deep, and either the
conductor itself or old iron chain carefully connected to its
foot should be laid therein, and the trenches should be
filled to a depth of 12 inches with coal ashes or other car-
bonaceous substance. (Do.)
(36.) Surface drainage should be led over the trenches.
(Do. 9.)
(37.) Tanks are useless. (Do. 10.)
68 LIGHTNING.
II. D 3844.
(38.) Any watertight tanks in existence should be
replaced by the above-named arrangements. (Do.)
(39.) As regards the use of iron earth connections with
copper rods, ' ' the contact of copper with iron will occasion a
rapid oxidation ofHhe latter metal." (Franc. Mich. Tel. 44.)
(40.) The rod is usually led into a well, and ends in two
or three ramifications to connect better with the soil.
(Gan. 833.)
(41.) If there is no well, a hole should be dug to a depth
of 6 or 7 yards, and the foot of the rod introduced, the
hole being filled up with wood ashes. (-00.)
(42.) In the case of the earths of telegraph wires " where
there are neither gas nor water pipes, an earth plate is
used ; a plate of copper buried upright in a narrow trench
filled with smith's ashes or wood charcoal, the object being
to expose as large a surface as possible." (Cull.)
(43.) Professor Pouillet's Committee in their report,
dated 19th February, 1855, stated: There should be
never-failing connection on the part of lightning rods with
water or moist earth, and to insure this, the earth connec-
tions should be divided into two arms, the first " going very
deep into the ground, into perennial water," and the second
"running nearer the surface." (And. 81.)
(44.) In explanation of the above, Professor Pouillet
wrote : "After a long continuance of dry weather it often
happens that the lightning-bearing clouds exert their
influence only in a feeble manner on a dry soil, which is a
bad conductor ; the whole energy of their action is reserved
for the mass of water which, by percolation, has formed
below it. It is here that the dispersion of the electric
force takes place." . . . "The case is entirely different
when, instead of dry weather, there have been heavy rains
moistening the earth thoroughly up to the surface. It is
the latter now that is the best, because the nearest, con-
ductor of the electric force, which will not go to the more
permanent sheet of water lying more or less deep in the
ground, if there is moisture above it." (-Do.)
NOTES ON LIGHTNING ENGINEERING. 69
II. D45 54.
(45.) The French prefer a moist soil to mere water con-
tact. (Do. 131.)
(46.) M. Callaud uses for an earth contact a galvanised
iron grapnel placed between two layers of charcoal. (Do.}
(47.) " Probably in nine cases out of ten wherever a
building provided with a conductor is struck by lightning,
it is for want of good earth." (Do. 198.)
(48.) Franklin, in a report dated 21st August, 1772,
regarding lightning rods for the Government powder
magazines at Purfleet, proposed to dig a well at each end
of each magazine, "in or through the chalk so deep as to
have in it at least 4 feet of standing water." (Do.
199.)
(49.) " To dwell too largely upon the importance of lead-
ing all lightning conductors down into moist earth, or as
technically called ' good earth,' would be scarcely possible."
(Do. 198.)
(50.) The designing of earth connections should always
be intrusted to experts. (Do. 210.)
(51.) "As regards the means of obtaining a good earth
connection, the first and in all cases most preferable is to
lay the conductor deep enough into the ground to reach
permanent moisture." (Do.)
(52.) When the quantity of moisture is deficient or
doubtful, " it will certainly be advisable to spread out the
rope so as to run in various directions, similar to the root
of a tree, likewise in search of moisture." (Do.)
(53.) "To protect any structure of great extent, it is
absolutely necessary to bring the conductor or conductors
deep enough into the earth to reach water." (Do. 212.)
(54.) In the case of a powder magazine standing on dry
soil, and with no stream or permanent moisture near,
" nothing remains under these circumstances but to multiply
the lines of underground connection to the utmost extent."
. . . . " Still it must never be forgotten that absolutely
good earth, in reference to lightning conductors, means
moisture or water." (Do. 215.)
70 LIGHTNING.
II. D 55, 56; E 1 5.
(55.) Iron water mains are recommended, if permanent
moisture cannot be obtained. (Do. 216.)
(56.) Franklin suggested lead for earth connections as
being less liable to consume with rust than iron. (Frank.
429.)
(E.) THE APPLICATION OF HODS.
(1.) " The case of a ship is very different from that of a
building. A ship is a prominent object, generally a con-
ductor, situated upon a plane, the sea. It thus, if a thunder-
cloud passes near it, at once reduces the line of resistance
between the sea (inner coating) and the cloud (the exterior
coating of the condenser), determining discharge." ....
" On the other hand, buildings form but an insignificant
feature in the large irregular area exposed to induction
from a charged cloud. Trees and buildings take but a
portion of the charges which, in the case of ships, have
fallen in their whole intensity upon them." (Preece, 342.)
(2.) A chimney lined with a thick layer of soot, up
which a current of heated air and volumes of smoke are
ascending, and terminated with a mass of metal (the grate),
is an excellent but dangerous conductor, for it ends in the
room and not in the earth. Hence so many indoor acci-
dents, and hence the duty of every householder, particu-
larly in exposed situations, to protect himself and his
family. (Do. 345.)
(3.) Many houses are already protected by the lead- work
of roofing and the iron rain-pipes descending to the drains.
(Do. 348.)
(4.) At a house at Painswick, near Stroud, Gloucester-
shire, a 2-inch wrought iron drain-ventilation pipe is used as
a conductor, carried 8 feet above the highest chimney, sur-
mounted by a copper vane and point, and connected with
the lead of the roof. (Do.)
(5.) For a sum of 2 an intelligent man can protect his
house. (Do.)
NOTES ON LIGHTNING ENGINEERING. 71
II. E6 15.
(6.) Professor Abel, F.R.S., having had considerable
experience of conductors attached to powder magazines,
was frequently astonished at the amount of complication
introduced, and fully agreed with Mr. Preece as to the use
of galvanised iron wire for conductors (see B. 27 29), and
he importance of a thoroughly good permanent earth.
(S. T. E. 357.)
(7.) Many accidents result from the want of a good earth
connection to chimneys and fireplaces. (Gait, S. T. E.
358.)
(8.) Well-built houses are generally protected from
lightning by the lead water-pipes and ridges about them,
and it is from that cause that so few accidents to well-
built houses are heard of. (Lat. Clark, S. T. E. 373.)
(9.) Underground magazines are usually in dry soil.
The main underground magazines of works of defence
should be fitted with conductors. This is unnecessary with
small expense underground magazines. Casemated bat-
teries with magazines in their basements should have
conductors. (W. 0. 1875, 58.)
(10.) Flagstaff s of coast batteries should have conduc-
tors. Iron shields of batteries must be connected with
conductors. (Do. 9.)
(11.) Asphalte and concrete roof coverings are non-
conductors. (Do. 10.)
(12.) A building of uniform height should have a pointed
rod, 5 feet above it, at intervals of 45 feet along its length.
If of iron, the point should be gilt. (Do. 29.)
(13.) Buildings not more than 20 feet long to have one
vertical conductor at the end, with a point 5 feet above the
roof, and a horizontal conductor along the ridge. (Do. 30.)
(14.) If 20 to 40 feet long, there should be one vertical
conductor in the centre, with a horizontal conductor along
the ridge. (Do. 31.)
(15.) If exceeding 40 feet long, there should be two
vertical conductors, and if exceeding 100 feet, three.
(Do. 32.)
72 LIGHTNING.
II. E 1624.
(16.) A diagram is given as an illustration of the manner
of defending a large powder magazine. The building has
four parallel ridged roofs with gable ends, and the follow-
ing system of rods :
(1.) 8 copper-pointed terminal rods, one at each
gable summit.
(2.) 4 horizontal copper ridge pieces, joining the
terminal rods.
(3.) 16 sloping copper gable end pieces, leading
from the terminal rods to the gutters.
(4.) 2 copper eaves-gutters at the sides.
(5.) 3 lead valley- gutters between the roofs.
(6.) 8 copper down-pipes from the gutters to earth.
(Do. 33.)
(17.) All parts of a building of marked elevation should
be fitted with conductors. (Do. 34.)
(18.) Where several conductors are used in a building,
they should be connected horizontally. (Do. 35.)
(19.) "All metal surfaces, whether of lead, copper, or
iron, in ridges, roofs, gutters, or coverings to doors or
windows, should be connected with the conducting system."
(Do.)
(20.) Materials of which buildings are composed are for
the most part conductors. (Harr. 94.)
(21.) It can be seen by experiment how walls of
buildings are conductors of electricity. (Do. 9.)
(22.) A wall is a protection to a house, and the rod
should be outside a building, and not inside. (Ar. 249.)
(23.) It having been observed that the minute dust of
gunpowder, liable to lodge on the projections and ledges
of powder magazines, was a source of danger, Toaldo, in
1776, suggested placing conductors at upright masts some
feet distant from the magazines. (Do. 251.) [See note to
G. 45.]
(24.) As many conductors as terminal rods are needed.
(Do. 247.)
NOTES ON LIGHTNING ENGINEERING. 73
II. E25 35.
(25.) It is advantageous to connect the bases of the rods
along the ridge of the roof, also any metals in the roof and
parapet. (Do.)
(26.) The use of insulating substances between the rod
and the house is now (1855) nearly given up, being recog-
nised as unnecessary and costly. (Do.)
(27.) The object of rods "is to permit a free neutralisa-
tion of the electric forces, and thus, as it were, to afford a
ready outlet to a violent agency that may do mischief to an
indefinite amount if not provided with such means of
escape." (Nek. A. M.)
(28.) In Gray Lussac's report to the French Academy in
1823, it was held that " all large metallic masses contained
in any building should be brought into metallic communi-
cation with the main system of conductors, and that there
was no need whatever for the employment of insulating
supports in attaching the lightning rod to the structures
that it is intended to defend." (Mann, 1875, 538.)
(29.) M. Callaud, in his recent treatise on "Paraton-
nerres," does not agree with this. He adopts insulating
supports, and he contends that the rod itself ought to be
quite sufficient, and that the metallic connections are
superfluous when it is efficient, and dangerous when it is
not. (Do.)
(30.) Lightning protection should not be carried near to
gas-pipes smaller than 1 inch in diameter, nor to any made
of soft metal. (Do. 1878, 332.)
(81.) " The lead roofing and all masses of metal in the
line of the probable discharge should be connected with
the rods." (Do. 347.)
(32.) Conductors need not always be outside a building.
(Do.)
(33.) In America, gutters, rain-pipes, and other metal
surfaces are much utilised as conductors. (And. 134.)
(34.) The large iron mineral oil tanks are protected by
conductors. (Do. 138.)
(35.) " The first point in designing the protection of a
74 LIGHTNING.
II. E 3641.
building will be clearly to ascertain what path the lightning
will take on its course from the clouds to the earth."
(And. 141.)
(36.) Mr. Anderson gives (but without an estimate) a
design ' ' for the protection of a large detached mansion by
means of a multiplication of short points, or terminal rods,
fixed on all the prominent features of the building. The
conductor is carried along the ridges in every direction,
and down the edges of the roof at each gable. Generally
it is sufficient to have two descending conductors, but occa-
sionally the conformation of the building, or the nature of
the ground, renders necessary the use of even more." (Do.
150.)
(37.) Franklin was at first in favour of having lightning
rods inside buildings. This plan was adopted in France
and on the Continent, but was soon abandoned. (Do.
158.)
(38.) The practice of insulating the rod from the build-
ing " is not only useless, but positively dangerous." (Do.)
(39.) There is a necessity "of leaving the design and
erection of lightning conductors to those persons who have
made a thorough study of the subject, since the work is by
no means so free from complexity as is commonly supposed."
(Do. 177.)
(40.) " The idea that persons may construct their own
conductors is left aside altogether as absurd." (Do. 216.)
(41.) As tending to show how little the application of
rods to buildings has been associated in England with the
architect's profession, it may be mentioned that the fol-
lowing well-known architectural works of reference
apparently contain no allusion to the subject of defence
from lightning, viz. :
(a) Nicholson's Architectural Dictionary, 1819.
(/3) Bartholomew's Specifications for Practical Architec-
ture, 1840.
(y) Glwilt's Encyclopaedia of Architecture, 1842.
NOTES ON LIGHTNING ENGINEERING. 75
II. E 42 ; F 16.
(8) Weale's " Dictionary of Terms used in Architecture,"
"Building," "Engineering," &c., 18589.
(e) Kerr's " Gentleman's House," 1865.
(42.) An iron building would be wholly free from
damage by lightning. We must, therefore, endeavour to
bring the general structure "as nearly as may be" into
the same state as if it were all of metal. (W. 0. 1858,
>. A. 3, 4, 5.)
(F.) INSPECTION OF EODS.
(1.) The state of the earth should be tested by means of
galvanometers. (Mann, 1875, 537.)
(2.) M. de Fonvielle has recommended an arrangement
of a short circuit wire, with a galvanometer, to be fixed to
each separate conductor, sp that an examination can
always be made. (Do.}
(3.) A convenient form of galvanometer for testing con-
ductors has been devised by Mr. E. Anderson. (Do. 1878,
339.)
(4.) Lightning rods should be periodically examined as
to points, continuity, and earth, and tested with a galvano-
meter and current. (Preece, 347.)
(5.) Frequent inspections are needed. (W. 0. 1875, 43.)
(6.) "Most of the lightning conductors in Paris have
been neglected for so many years that they are positively
dangerous, instead of being useful protecting apparatus.
When examined with a strong magnifying glass, the points
of the stems are blunted or burnt (a criterion of the bad
conduction of the communications), and the points have
fallen from several, or rather, having been badly joined,
the solder has failed, and they only hold together by the
pins ; the vibrations of the stem when agitated by the wind
have worn away the connections, so that a great number
are easily shaken by the hand. The contact is very bad,
E 2
76 LIGHTNING.
II. F7 15.
consequently the preventive effect of the apparatus is
absolutely null. But these great deteriorations are not
confined to the stems, since the point of juncture of the
conductor to the base of the stem is almost everywhere in
a deplorable state. This juncture I have always found to
have been made with a strap or iron collar, whose pieces
are rusted, so as to render the electric communication next
to nothing." (Franc. Mich. Tel. 44.)
(7.) The joints of the above rods being badly arranged,
have been affected by the dilatation and contraction due to
variations of temperature. (Do.}
(8.) " Where the conductor penetrates the soil it is not
covered with any protecting substance ; so that the alter-
nation of dryness and moisture in the soil deeply corrodes
the iron and ultimately cuts it through." (Do. 45.)
(9.) Without periodical tests, " there is really no trust-
worthy security of protection in lightning conductors."
(And. 61.)
(10.) The French committee who reported on the 14th
January, 1867, stated that conductors, to be efficient,
should be regularly inspected, at least once every year.
(Do. 84.)
(11.) The conductors of Westminster Palace have never
been tested since they were fixed. (Do. 120.)
(12.) The inspection of conductors after once they are
put up is generally overlooked in this country. (Do.
218.)
(13.) The regular inspection of lightning conductors, as
yet unknown, or all but unknown, in England, has been
for a long time in practice in several States of Continental
Europe, among them Germany and France. (Do. 222.)
(14.) "There is really nothing else to make a lightning
conductor a safe protection under all circumstances, and
at all times, but regular, constant, and skilful examina-
tion." (Do. 226.)
(15.) The writer recently tested 16 "earths" of the
lightning conductors of some large powder magazines with
NOTES ON LIGHTNING ENGINEERING. 77
II. G 17.
one cell of a Le Clanche battery and an ordinary vertical
detector galvanometer, all the arrangements being made by
a practised telegraphist. The " quantity " coil of the gal-
vanometer gave no deflection at all for any of the "earths,"
and the " intensity " coil gave about 2 for those tried with
it. On a subsequent occasion one of the same " earths"
was tested with 3 Le Clanche cells, and a 3 -coil galvano-
meter, by the 10 coil of which a deflection of from 25 to
35 was registered.
(Q-.) THE PROTECTIVE POWERS OF EODS.
(1.) The Section of Physic of the French Academy,
consulted in 1823 by the Minister of War, considered that
a rod protected a circular space whose radius was equal to
twice its height. (Ar. 237.)
(2.) Arago knew of no case in which pointed conductors
had failed to preserve buildings from damage, in which
there had not been palpable errors of construction. (Do.
264.)
(3.) In 1765, the physicist, Nollet, opined that rods
attracted lightning, and occasioned it to strike a house
more frequently than would otherwise be the case. (Do.
265.)
(4.) Another physicist, Wilson, supported this view.
He and Nollet thought that rods were, on the whole, more
dangerous than useful. (Do.)
(5.) A definite radius of protection could not always be
assigned to rods ; and experience showed that their influ-
ence was only in furnishing " an easy line of conduction "
to the discharge. (Harr. 117.)
(6.) The cases in which buildings with rods had been
damaged, bore only ' ' a small proportion to the great mass
of instances in which lightning falling on buildings has
struck on the conductors attached to them." (Do. 120.)
(7.) In 1838, the East India Company, owing to the
78 LIGHTNING.
II. G8 14.
representations of their scientific officers, ordered the rods
to be removed from their powder magazines and other
public buildings. (Do. 176.)
(8.) In a work published in 1829 by a Civil Engineer in
the Government service, entitled " Three Years in Canada,"
the following passage occurred: " Science has every
cause to dread the thunder rods of Franklin ; they attract
destruction, and houses are safer without them than with
them." (Do. 177.)
(9.) Harris says that the theory just mentioned is not
warranted by any sound argument drawn from experience.
(Do. 184.)
(10.) It is inferred from "the fact of so many buildings
being repeatedly struck by lightning before they are
furnished with lightning rods, and so seldom struck after-
wards, and from the fact of lightning having seldom, if
ever, been observed to fall in an explosive form upon
buildings involving pointed metallic conductors in the con-
struction," that the rods had "rapidly neutralised the
electrical state of the air and so prevented the occurrence
of a dense explosion." (Do. 189.)
(11.) In the experience of nearly half a century, "not a
single case can be adduced in which a lightning rod, in the
act of transmitting a heavy charge of lightning, had
thrown off a lateral explosion on semi-insulated masses
near it." (Do. 201.)
(12.) Faraday had stated (previously to 1843) that he
was "not aware of any phenomenon called lateral dis-
charge which is not a diversion of the primary current."
(Do. 208.)
(13.) "The few accidents on record can scarcely be
urged as an objection to the general principle, especially
when we take into consideration the great number of
lightning rods set up in various parts of the world." (Do.
224.)
(14.) "The lightning stroke is certainly more likely to
fall where a lightning conductor, of whatever kind, is
NOTES ON LIGHTNING ENGINEERING. 79
II. G 1523.
placed, than it would be if there were no such appliance."
(Mann t 1875, 333.)
(15.) " The old dogma, that a conductor does not attract
electricity, is open to modification. The induction draws
a strong charge to the top of the rod, and thus brings
about a stronger tendency to discharge." (Do. Times, 23
NOG. 1877.)
(16.) It is doubtful if a conductor of insufficient size
is better than none at all. (Do. 1875, 533.)
(17.) Attention is called by Dr. Mann to the cases of
tall chimney-stacks with conductors being struck ; and
this he attributes to the frequently insufficient size of the
latter, which causes the discharge to leap through the
brickwork to the soot-covered surface within. (Do.)
(18.) When the point is blunt, or the earth contact bad,
rods attract lightning. There is no attraction in a well-
constructed conductor. (Do. 1878, 330.)
(19.) It is contended that the usual view of a conical
space being protected by a conductor is not trustworthy ;
and the only absolute protection is to cover the entire
structure with intermeshed lines of defence. (Do.)
(20.) After the city of Pietermaritzburg, in Natal, had
been largely supplied with pointed lightning conductors
under Dr. Mann's fostering influence, "the actual dis-
charge of violent lightning strokes within the area of the
town became almost unknown." (Do. 1875, 335.)
(21.) The radius of cone protected by a conductor should
be taken at half the height of the conductor. (Preece, 348.)
(22.) " The methods that have been adopted for protec-
tion, based upon the damage inflicted on ships, have pro-
bably led to the adoption of unnecessarily costly and super-
fluous measures to protect buildings and instruments."
(Do. 342.)
(23.) "As regards ships, the method adopted by the
great authority, Sir William Snow Harris, has proved
itself so efficient and perfect that no improvements have
been required, nor can any well be suggested. . . . Such
80 LIGHTNING.
II. G24 32.
vessels as have been struck have been invariably un-
protected." (Do. 344.)
(24.) It is " sufficiently correct for practical purposes " to
take the protective radius of the conductor the same as its
height above the ground ; but this cannot always be relied
on. (W. 0. 1875, 26.)
(25.) " Conductors of themselves have no attraction for
lightning, which seeks them only on account of the facility
they afford for the combination of the opposed states of the
electricity of the clouds and the earth beneath them, sepa-
rated by the atmosphere, which is a bad conductor."
(Do. 27.)
(26.) "A lightning conductor, buildings, trees, or any
object on the surface of the earth is only to be regarded
as diminishing the resistance due to the air." (Do.)
(27.) "When an electrified cloud is passing over the
earth, and its potential is just counteracted by the resis-
tance of the air, a body, however small, which reduces the
resistance will cause a discharge." (Do.)
(28.) "Even a change in the nature of the soil over
which the cloud is passing may have this effect on it."
(Do.)
(29.) " It is very frequently produced by a fall of rain."
(Do.)
(30.) An angle of a building may receive a discharge,
while another angle is provided with a conductor. Im-
portant buildings containing explosive materials should
have every prominent elevated part provided with a con-
ductor. (Do. 28.)
(31.) "A conducting rod, in whatever way it may be
applied, is to be considered merely as a means of perfect-
ing the conducting power of the whole mass so as to admit
of intense discharges of lightning being securely trans-
mitted, which otherwise would not pass without interme-
diate explosion and damage." (Do. 94.)
(32.) The idea of lateral discharge from conductors is
absurd. (W. 0. 1858, App. A. 8.)
NOTES ON LIGHTNING ENGINEERING. 81
II. G 3340.
(33.) Masonry, ships' masts, and lightning conductors
transmit a certain quantity of electricity without explosive
action. The conductor relieves the wood and the masonry.
(Do. App. B. 2.)
(34.) Experience having shown, soon after the introduc-
tion of conductors, that by their use lightning became
without effect, "it was thought that storms might be
dissipated if a sufficient number of paratonnerres were
raised, so as to neutralise the electricity of the atmosphere."
The houses at Zurich are studded with paratonnerres.
(Eaem. 353.)
(35.) M. Viollet-le-Duc, the distinguished French archi-
tect, considers it prudent to put up two rods on a typical
country house (the design and construction of which is the
subject of his book), since the recognised theory is that
" lightning conductors only protect the points enclosed in
a cone of which they are the summit." ( Violl. 253.)
(36.) " Between ourselves, physicists are not quite
agreed respecting the effects of the electric fluid, the rela-
tive efficiency of conductors, and the precautions to be used
in putting them up." (Do.)
(37.) "I rely on my own experience which has proved
to me that no building, however exposed, has been struck
by lightning when the lightning rods were numerous, made
of good conductors, put in communication with each other,
and with their lower extremity dipping in water or very
damp earth." (Do.)
(38.) M. Viollet-le-Duo does not see the advantage of
using insulators. (Do.)
(39.) " Projections such as trees, spires, lightning con-
ductors, lead off the negative electricity of the ground
quickly, thereby diminishing its tension, and conduct the
electricity of the clouds to the earth without violence."
(R. E. A. 56.)
(40.) As regards the lightning conductor, "the advan-
tage gained by it consists, not in protecting the building in
case of a discharge by allowing a free passage for the
E 3
82 LIGHTNING.
II. G4i_46.
electric fluid to escape to the earth, for it is but a poor
protection in such a case ; but in quietly and gradually
keeping up the communication it tends to maintain the
electric equilibrium, and thus to prevent the occurrence of
a discharge." (Such. 300.)
(41.) The result of the report of the committee of the
French Academy in April, 1823, that rods would protect a
circular area of a radius double their height, led to rods of
enormous height being erected. (And. 77.)
(42.) The French Committee of December, 1854, reported
through M. Pouillet that the theory of a fixed area of
protection was inadmissible. (Do. 78.)
(43.) They gave as their reason the varying shapes of
buildings and materials of construction, and said "it is
clear, for example, that the radius within which the con-
ductor gives protection, cannot be so great for an edifice,
the roof, or upper part, of which contains large quantities
of metal, as for one which has nothing but bricks, woods,
or tiles." (Do. 79.)
(44.) They also said "a lightning conductor is destined
to act in two ways. In the first place, it offers a peaceful
communication between the earth and the clouds, and by
virtue of the power of points the terrestrial electricity is
led gently up into the sky to combine with its opposite.
In the second, it acts as a path by which a disruptive dis-
charge may find its way to the earth freely." (Do.)
(45.) The French Commission who reported on the 14th
January, 1867, as regards powder magazines, stated "that
the best protection against lightning would be afforded by
the most substantial metal rods ; made of iron, surrounding
a building on all sides, and passing deep into the ground."*
(And. 84.)
(46.) In a work entitled "Three Years in Canada,"
published in London in 1829, Mr. F. McTaggart, C.E.,
* Gmllemin, in his " Application of Physical Forces," says that
these rods are proposed to be attached to wooden masts separated from
the magazines.
NOTES ON LIGHTNING ENGINEERING. 83
II. G47 50.
wrote about lightning rods, " Were they able to carry off
the fluid they have the means of attracting, then there
could be no danger ; but this they are by no means able to
do." (Do. 92.)
(47.) The general presumption in France is that "a
terminal rod will protect effectually a cone of revolution of
which the apex is the point of the rod, and the radius of
the base a distance equal to the height of the said rod
above the ridge multiplied by 1-75." (Do. 126.)
(48.) " The function of a lightning conductor is twofold,
In the first instance, it operates as a medium by which ex-
plosions of lightning, or, to speak more accurately, dis-
ruptive discharges of electricity, are led to the earth freely.
In the second instance, the conductor acts as a means
whereby the accumulation of electricity existing in the
atmosphere is quietly drawn off and carried noiselessly
into the earth, and dissipated in the subterraneous sheet of
water beneath it." (Do. 142.)
(49.) Professor J. Clerk Maxwell, F.R.S., has proposed
a system of lightning protection without points or earth
connections. He says, " What we really wish to prevent is
the possibility of an electric discharge taking place within
a certain region say in the inside of a gunpowder manu-
factory. . . . An electrical discharge cannot take place
between two bodies unless the difference of their potentials
is sufficiently great compared with the distance between
them. If, therefore, we can keep the potentials of all
bodies within a certain region, equal, or nearly equal, no
discharge will take place between them." (Do. 164.)
(50.) To do this he proposes " to enclose the building
with a network of good conducting substance. For in-
stance, if a copper wire, say No. 4, B. W. Q-. (0-238 inches
in diameter), were carried round the foundation of the
house, up each of the corners and gables, and along the
ridges, this would probably be a sufficient protection for
an ordinary building against any thunderstorm in this
climate." (Do.)
84 LIGHTNING.
II. G51 54.
(51.) In respect of lightning rods generally, Mr. Ander-
son says, ''Subject to the constant effects of moisture, to
wind, ice, and hailstorm, there is always a possibility of
the slender metal strips being damaged so as to interrupt
their continuity and thus destroy the free passage of the
electric force. Instances have happened in which the
damage done was so slight as to be scarcely visible, and
still to destroy the efficacy of the conductor." (Do. 219.)
(52.) The improved drainage now going on everywhere
constitutes a serious danger to lightning conductors, since
the moisture is being sucked out of the ground. (Do.}
(53.) " Constant alterations in the interior of buildings,
private residences, as well as public edifices, may serve to
destroy the efficacy of a conductor which was originally
good even to perfection. Thus a roof may be repaired,
and lead or iron introduced where it was not before ; or
clamps of iron may be inserted in the walls of houses, to
give them greater strength ; or in fact any changes may
be made which bring masses of metal more or less in
proximity to the conductor There are hundreds of
instances to prove that changes made in buildings such as
the addition of a leaden roof without, or the iron balustrade
of a staircase within, diverted the current of the electric
force from the conductor on its way to the earth, originally
well provided for." (Do. 220.)
(54.) "A lightning rod protects a conic space whose
height is the length of the rod, whose base is a circle
having its radius equal to the height of the rod, and whose
side is the quadrant of a circle whose radius is equal to
the height of the rod." ..." There are many cases where
the pinnacles of the same turret of a church have been
struck where one has had a rod attached to it ; but it is
clear that the other pinnacles were outside the cone, and
therefore, for protection, each pinnacle should have had
its own rod. It is evident also that every point of a build-
ing should have its rod, and that the higher the rod, the
greater is the space protected." (Preece, Tel. 15/12/80.)
NOTES ON LIGHTNING ENGINEERING. 85
II. G55,56.
(55.) A conductor of insufficient sectional area, " if con-
nected with the earth, would protect a house from injury,
though it might itself be destroyed." (Lat. Clark, S. T. E.
374.)
(56.) Mr. Graves recommends erecting numerous light-
ning conductors everywhere, especially upon high hills and
high buildings, in order, so far as possible, to prevent the
occurrence of thunderbolts. (Cfrav. S. T. E. 413.)
NOTE. Whilst this work was passing through the press, the Eeport
of the " Lightning Rod Conference " (London : Spon, 1882) was pub-
lished. The Report is dated 14th December, 1881, and is signed by
delegates from the Meteorological Society, the Royal Institute of
British Architects, the Society of Telegraph Engineers and of Elec-
tricians, and the Physical Society. The Report says, "A light-
ning conductor fulfils two functions : it facilitates the discharge of
the electricity to the earth, so as to carry it off harmlessly, and it
tends to prevent disruptive discharge by silently neutralising the con-
ditions which determine such discharge in the neighbourhood of the
conductor." The points must be "high enough to be the most
salient features of the building, no matter from what direction the
stormcloud may come." The following instructions are given :
Tops of rods to be blunt, but 1 foot below them a copper ring with
three or four sharp copper points to be fixed points to be either
platinised, gilded, or nickel plated ; the best material for rods is cop-
per ; the best form is a copper rope \" diameter, or a copper tape
t " X i" 5 joints to be always soldered ; iron rods to be painted (except
at points) even if galvauised ; insulators not to be used ; gas and
water mains to be utilised as earths ; earth plates to be of the same
metal as the rods, to be at least 9 square feet in area, and to be sunk
in holes so deep that the earth around them is always moist ; in rocky
sites, besides earth plates, 3 or 4 cwt. of iron to be buried at the foot of
rod ; the space protected by a rod is a cone with a base having a radius
equal to the height of rod ; rods must periodically be examined
visually and tested electrically ; internal masses of metal (except soft
metals and gas-pipes) to be connected to earth, or to the rod ; external
masses of metai to be connected to each other and to earth direct, or
to the rod.
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THE THEORY OF THE ACTION OF
LIGHTNING.
CHAPTER V. ELECTRICAL DEFINITIONS AND
DATA.
(A.) ELECTRICAL DEFINITIONS.
(a) Fundamental Terms.
(1.) Electricity is a temporary state of forced separation
of a physical property, normally dormant in all bodies,
into two active agencies, each, possessed of a power due
to a tendency to reunite. 1
(2.) Positive electricity, or positive charge, and negative
electricity, or negative charge, are the names given to the two
agencies respectively. 2
(3.) An electrified body, or a charged body, is one in which
either of the electricities is present.
(4.) Quantity is the form of agency present with electri-
city of either nature. 3
(5.) Potential is the form of power present with electri-
city of either nature. 4
(6.) Capacity is the form of restraint present with electri-
city of either nature. 5
1 I. A . 2 II. A 19. 3 I. A 6, 7, 10.
4 I. A 6, 7, 10. s L A 6) 7> 10 .
N.B. These footnotes are references to other Chapters, Sections,
and Taragraphs.
146 LIGHTNING.
Y. A 717.
(7.) Attraction is the property which electricity of one
nature has for that of another.
(8.) Repulsion is the property which electricities of the
same nature have for each other. 1
(9.) A collector is a body qud its property of permitting
electricity on it to distribute itself, and hence to accumu-
late. 3
(10.) An insulator is a body qud its property of prevent-
ing electricity on it from distributing itself, and hence
from accumulating. 3
(11.) A conductor is a body qud its property of permitting
electricity to be transmitted through it. 4
(12.) Discharge is the act of reunion of two electricities
of different natures, involving the execution of work, and
the restoration of the bodies on which the charges were
collected to their normal passive state.
(13.) An explosion is an instantaneous discharge through
an insulator. 5
(14.) A return stroke is an instantaneous discharge
through a collector, occasioned by a reunion of the two
electricities originally separated. 6
(15.) A leak is a continuous discharge through an insu-
lator. 7
(16.) Electro-motive force is the force manifested in the
obliteration of difference between the potentials, or the
states of potential, of two electrified bodies when joined by
a conductor. 8
(17.) A current is a transmission of electricity by electro-
motive force through a conductor; and it comprises all
discharges through a conductor, whether instantaneous or
continuous. 9
1 I. A 2. 2 I. A 15. 3 I. A 1416.
* I. A 15. 6 I. A 2731. 6 I. D 51.
7 I. A 16. 8 I. A 8, 13. 9 I. A 8, 13.
ELECTRICAL DEFINITIONS AND DATA. 147
Y. A b c 1830.
() The Influence of Bodies.
(18.) Influence is the inherent property, manifested by
various actions, that bodies possess for affecting electricity.
(19.) Collection is the action of distributing electricity
and of imparting by it electricity of the same nature. 1
(20.) Induction is the action of imparting one kind of
electricity by means of the other. 2
(21.) Insulation is the action of isolating or enveloping
electricity, and of limiting its distribution. 3
(22.) Facilitation is the action of hastening explosion, and
of transmitting its operation without obstruction.*
(23.) Restraint is the action of delaying explosion and of
obstructing its operation. 5
(24.) Conduction is the action of transmitting current. 6
(25.) Resistance is the action of retarding current. 7
(c] The Nature of Condensers.
(26.) A condenser is such a juxtaposition of two col-
lectors, one of which is electrified from some extraneous
source, that by means of mutual induction through the
separating insulator the potential of the electricity is
appreciably raised. 8
(27.) A collecting plate of a condenser is the surface, nearest
to the insulator, of the collector which receives its original
charge from some extraneous source.
(28.) A condensing plate of a condenser is the surface,
nearest to the insulator, of the collector which receives its
original charge by induction from the other collector.
(29.) A dielectric of a condenser is the insulator separating
the collecting from the condensing plate. 9
(30.) An explosion of a condenser is an instantaneous dis-
1 I. A 15. 2 I. A 1721. 3 I. A 1416.
* I. D 2, 6. * I. A 27. I. D 17. 6 I. A 15.
7 J. A 8. 8 I. A 2126. 9 I. A 24.
H2
148 LIGHTNING.
V. A 31, 32; B 1.
charge, through, the dielectric, of the electricities accumu-
lated on the plates. 1
(31.) A return stroke in a condenser is an instantaneous
discharge of the electricity on one of its plates, through
the plate itself, owing to the electricity on the other plate
having become discharged by some extraneous means. 2
(32.) A leak in a condenser is a continuous gradual dis-
charge, through the dielectric, of the electricities accumu-
lated on the plates. 3
(B.) ELECTRICAL DATA.
(a) Electrical Formula.
(1.) The following formulae express mathematically the
chief laws on which electrical science is based. 4
/. Fundamental.
= m.
Distance = /.
Time = t.
IX. Mechanical.
rr 7 -, distance I
Velocity = v = ^ = .
X time t
JcHkrM* = a = Telocity = J :.
time t-
Force ==/= acceleration x mass = w = .
p
?FbrA = w = force X distance =// = -^-.
///. Electrical.
1 73
Quantity = q =. Vforce X distance = /4J =: - a
1 I. A 27, 29, 30. 2 I. D 5158.
3 I. A 16, C 88. II. D 11. * I. A 611.
ELECTRICAL DEFINITIONS AND DATA. 149
V. B I 25.
T> . , 7 work
Potential = p = - -
quantity
ill
[Hence potential =: \/'orce.
Capacity = . = *"*" = f =
potential p t
[Hence capacity = distance.]
Electro-motive force = e difference of potential = jt>.
R I _
time ^ t
electro-motive force e
current c
(i) The Three Elements of Electricity.
(2.) Quantity, potential, and capacity are the three
essential elements of electricity. 1
(3.) The basis of electrical law is the expression denot-
ing quantity, which is derived experimentally from the
amount of force of repulsion or attraction developed be-
tween two small electrified bodies placed at a certain dis-
tance apart. 2
(4.) Potential is the impelling or moving quality of
electricity. It is the measure of the capability that elec-
tricity has of doing work, in proportion to its quantity. 3
(5.) Capacity is the restraining or limiting quality of
electricity. Its action is directly antagonistic to that of
potential. It is the element that allows of the electricity
being tangible. 4
1 I. A 7. 2 I. A 6. I.A 10. * I. A 10.
150 LIGHTNING.
V. ~Bcd6ll.
(<?) Collectors and Insulators.
(6.) Every electrical system consists of two collectors
separated by an insulator. 1
(60.) Every electrified body consists of a collector en-
veloped by an insulator. 2
(7.) The capacity of an insulator consists of three factors,
and varies directly as each of them, viz. :
(a) Surface, or the extent of area of the insulator, qud
the collector. 3
(/3) Thickness, or the distance of the surface of the col-
lector from that of the nearest collector from which
it is separated by the insulator. 4
(y) Restraint, or " specific inductive capacity ; " i.e. the
specific influence due to the material of the insu-
lator. 6
(8.) A body which has one of the three characteristics of
being a quick collector, a great facilitator, or a good con-
ductor, necessarily possesses the other two characteristics.
(9.) A body which has one of the three characteristics
of being an insulator, a restrainer, or a non-conductor,
necessarily possesses the other two characteristics.
(d) Electrical Explosions.
(10.) The potential and capacity present with any elec-
trified body always balance each other, and the loss of
balance constitutes discharge. 6
(11.) An explosion of a condenser occurs when the
potentials of the charges separated on the two plates have
accumulated to such a degree that the capacity of the
dielectric is unable any longer to restrain their junction.
i.e. to balance the combined effect of the two potentials. 7
1 I. A 6. V. A 4, 6 ; B 3. * I. A 20. V. A 6.
3 I. A 25, 26. V. A 23. * V. A 6 ; B 5.
5 I. A 6. V. A 6; B 5. 6 I. A 7.
7 I. A 29, 30 ; D 11, 16, 17. II. C 27 ; V. A 13.
ELECTRICAL DEFINITIONS AND DATA. 151
Y. IU/12 16.
(12.) From the formula capacity- quantity , 1 it follows
potential
that potential == quant ! ty ; hence potential is liable to be
capacity
affected by alterations to quantity and capacity ; but since
capacity varies as surface, thickness, and restraint, and
these conditions cannot affect, or be affected by, the quan-
tity of electricity present, it is evident that, in any given
electrical system, alterations to quantity, surface, thickness,
or restraint, will always alter potential.
(e) Electrical Return Strokes.
(13.) If one of the plates of a condenser becomes dis-
charged by means of explosion with a plate of an adjacent
condenser, so much of the charges on each of the remain-
ing plates of the two condensers as was due to the induc-
tion of the discharged plates necessarily reunites through
itself with the complementary electricity from which it was
separated by the action of induction. 2
(14.) This action of return, or recombination, is of a
nature not unlike that of a current, and constitutes a return
stroke or induced discharge.
(/) Electrical Leaks.
(15.) In practice, perfect insulators do not exist; and
there are two kinds of leaks to which all insulators, and
hence all dielectrics, are subject. 3
(16.) In the first place, they all leak, in inverse propor-
tion to their specific restraint, through the electric pores of
their material. 4 Hence, in every condenser, the charges
on the two plates are continually, slowly, and silently
rejoining each other, but frequently in so comparatively
small a degree that the general conditions of the condenser
1 I. A 10. V. B 1. 8 I. A 5158, 6671. V. A 14.
3 I. A 16. V. A 15. * V. B 7.
1 52 LIGHTNING.
V. B^ 1721.
are perhaps not, till after a considerable time, materially
affected.
(17.) Secondly, they leak through the indentations on
their surfaces caused by projecting angularities on the
surfaces of the collectors they envelope, and in direct pro-
portion to the number and acuteness of these angularities.
(18.) Thus, wherever a point, angularity, or indeed any
salient deviation from a uniform surface, occurs on the
face of a collector, there, in proportion, capacity ceases,
potential becomes infinite, and discharge occurs, 1 although
the rate at which electricity is thus lost may be extremely
slow. 8
(19.) If the collector be so shaped as in itself to constitute
an acute angularity, or point, and if it moreover consist
of highly collective material, as metal, the entire charge
on it quickly disappears.
(20.) The inherent power of a point on a collector to
eject charge therefrom is quite independent of the proxi-
mity of any juxtaposed collector. 3
(g} Illustrations of Electrical Action.
(21.) It may serve to strengthen the ideas if we illustrate
the leading elements of electro-static action by means of
hydraulic engineering similes. 4 The following table shows
this comparison :
Electric Element. Hydraulic Simile.
Condenser Keservoir formed by a dam
constructed across a gorge.
Collecting and condensing Bottom and sides of the reser-
plates. voir.
Dielectric Dam retaining the water in the
reservoir.
1 V. B 10. 2 II. C 11, 17, 2628, 3739, 51, 5355.
3 II. C 39, 51, 5355. V. B 15. 4 I. A 12. II. C 51.
ELECTRICAL DEFINITIONS AND DATA.
Electric Element.
153
Charge on the plates ....
Potential of the charge . . .
Capacity of the dielectric . .
Discharge of the plates . . .
Explosion of the condenser . .
Porous leak in the condenser .
Angular leak in the condenser.
Hydraulic Simile.
Body of water in the reservoir.
Head of water in the reservoir.
Dimensions and material of the
dam.
Escape of the water by any
means.
Bursting of the dam through
the pressure of the water.
Porosity of the material of tha
dam.
Sluice, or pipe, through the
dam.
H 3
VI. A a.
CHAPTEE VI. THE CONSTITUTION OF THE
TEEEESTEIAL CONDENSES,
(A.) THE FUNCTION OF THE EARTH IN THE TERRESTRIAL
CONDENSER.
(a) The Relation between the Earth and the Clouds.
DURING, and immediately previous to, a thunderstorm,
the earth, atmosphere, and clouds, constitute a great
natural electric condenser, of which the earth and clouds
are the two plates, and the intervening atmosphere is the
dielectric ; and the explosion of this condenser is manifested
under the form of shafts of lightning, accurately termed
thunderbolts. 1
It is of importance that we should have a clear percep-
tion as to which of these two plates it is that collects the
electricity, and which condenses it.
According to the theory generally accepted, the clouds
collect or originate the electricity of thunderstorms, whilst
the earth acts as the condensing plate. 2
It is assumed that the clouds receive their charge by
collecting from the upper regions of the atmosphere the
electricity perpetually being evolved from the surface of
the earth through decomposition, evaporation, and other
chemical actions, 3 and that the earth receives its charge
only by induction from the clouds.
The theory that the earth forms the condensing plate of
the terrestrial condenser is probably based on the fact of
1 I. D 1, 2, 11, 15, 16. II. El. V. A 2630 ; B 11, 21.
3 I. D 11; 049. IT. C 43. 3 I. C 10 14, 34.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 155
VI. A a.
the necessary arrangement of artificial condensers, wherein
the condensing plate is connected to the earth, by which
means the electricity on this plate, complementary of the
charge induced by the collecting plate, can be driven into
the earth, thus affording room for the induced charge to
attain its maximum potential.
But the principle of the condenser is clearly that of in-
duction, and does not depend on the fact of the condensing
or induced plate being connected with the earth ; ] in
other words, it does not depend on the earth itself forming
the condensing plate.
Doubtless an artificial condenser of any practical value
could hardly be formed unless the condensing plate were
thus formed by the earth ; but in the case of the great
natural condenser of which the earth directly constitutes
one of the plates, and the clouds the other, the circum-
stances are not the same.
All telegraphic and electric experience tells us that the
earth itself is a great reservoir of electricity, 2 and such
being the case, it would seem only natural that the elec-
tricity in this reservoir should occasionally be collected at
places on its surface ; but if this should happen, it is
necessary by electric law that charge of an opposite nature
should be induced on the nearest separate collector. 3
Now the nearest separate collectors to the earth's sur-
face during the existence of ordinary thunderstorm condi-
tions are certainly the clouds. Hence, supposing that,
owing to the action of the electricity within the earth,
charge should accumulate at places on the earth's surface,
charge of an opposite nature must always be induced on
the surfaces of the clouds nearest to these places ; and thus
with the earth's surface as the collecting plate, the nearest
clouds as the condensing plate, and the insulative regions
of air between them as the dielectric, we should obtain the
terrestrial condenser.
1 I. A 21. a I. C 5255. 3 I. A 21. V. B 7-
156 LIGHTNING.
YI. A b.
But there is good ground, based on the phenomena of
aurorse, 1 of heat (or sheet) lightning, 2 of lightning attending
volcanic eruptions, 3 and of thunderbolts occurring in clear
skies,* for believing that the upper regions of rarefied air
do actually (owing probably to induction by the earth)
form to some extent a reservoir of electricity independent
of the clouds, and any conduction of electricity upward
from the earth's surface, due to the process of chemical
evolution, would doubtless tend to promote the formation
of such a reservoir. 5
All the functions that the earth fulfils towards artificial
condensing plates would thus be fulfilled by this atmo-
spheric reservoir towards the clouds ; and these would be
enabled to act efficiently as condensing plates to the great
collecting plate of the earth's surface. 6
The fact that the greater proportion of lightning occurs
between cloud and cloud rather than between cloud and
earth, 7 will not militate against the idea of the clouds
receiving their charges by induction from the earth, if it
be borne in mind that two of the great observed elements
of the clouds are their detachment from each other in sepa-
rate masses, and their mobility. 8
Their separateness permits them to hold distinct insu-
lated charges, and to form fresh condensers with each
other; 9 whilst their mobility occasions more chances of
their being driven within explosive range of each other
than of the earth, which relatively is fixed.
(*) The Earth's Electricity.
We appear to have primd facie grounds for believing
that the earth's surface is really the collecting plate of the
terrestrial condenser, from the fact, already mentioned, of
1 I. C77, 7. 3 I. D 4, 20. s I. C 114, 115, 118 120.
4 III. 1, 2, 50. I. C 4. 5 I. B 4 j C 35.
6 I. C 34. 7 I. D 16. VI. B a.
* I. C 31, 33. a I. C 33.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 157
VI. A b.
electricity being contained within the earth ; but the ques-
tions now arise, what is the original source of the earth's
electricity, and how does its surface collect it ?
In our present state of knowledge it seems to be impos-
sible to get beyond conjecture in replying to such ques-
tions. 1
Supposing, however, that we take up the opposite view
that the clouds form the collecting plate, the task of at-
tempting to prove how they originate and collect their
electricity would appear to be even more hopeless ; for,
although we reasonably infer that the clouds are collectors
of electricity, we do not know the fact for certain ; and d
fortiori we must be ignorant of how the electricity got
there.
But we do know with certainty several important facts
regarding the earth's electrical constitution ; one is (as
already mentioned) that it is a great holder of electricity ; 2
a second, that it is a great collector and conductor of elec-
tricity ; 3 a third, that portions of its surface are constantly
found to be electrified ; 4 a fourth, that it is a great mag-
net ; 5 and a fifth, that terrestrial disturbances, such as
waterspouts, earthquakes, and volcanic eruptions, are con-
nected with the actions of electricity or magnetism. 6
We have thus, in our investigations as to the probability
of the earth being the originator of thunderstorms and
lightning, several scientific data to work upon, which are
quite wanting in regard to the clouds; and we propose
now to make a few remarks on the possible nature of the
earth's electrical actions, with the view of strengthening
the likelihood of the theory that its surface is the collecting
plate of thunderstorm condensers.
As to how the earth obtains its electricity or how it
became a magnet, we are practically in total ignorance. 7
1 I. C 2, 7173. 2 I. C 52, 53. 3 I. C 50, 5.1.
* I. C 6, 9. 5 I. C 63. 6 I. C , *, l.\
7 I. C 71 73.
158 LIGHTNING.
VI. A b.
The fact, however, that it is simultaneously both a
holder of electricity and a magnet is well worthy of atten-
tion ; and so also is the fact that phenomena undoubtedly
electrical, i.e. earth currents and auroree, are invariably
accompanied by magnetic disturbances. 1
It is well known that what is generally called magnetism
is so closely allied with electricity that the one produces
the other, that in some respects the action of magnetism is
the same as that of an electro-static charge, or of electricity
at rest, whilst in others its action is the same as that of
electricity in motion.
Owing to this last fact, magnetism has already been
conceived to be a series of electric currents, and the earth's
magnetism has been considered to be due to the never-
ceasing motion of these currents around it. 2
But may we not take a simpler view of the matter and
conceive the subtle force usually called magnetism to be
nothing but electricity, i.e. electricity bound or manifested
in a peculiar manner, and magnetism itself as only a pro-
perty or influence analogous to conductivity or inductive
capacity, appertaining to certain bodies, and permitting
this particular manifestation ?
All the special characteristics of magnets could appa-
rently be comprised by such a theory, for electric currents
cannot exist without electricity ; in other words, electricity
in motion does not cease to be electricity.
The actions of magnets would then be considered as
electrical actions, due to their occurring on a magnetic
body, on the same principle as other actions of electricity
are due to the fact of their occurring on insulating or con-
ducting bodies.
On this principle, then, the earth is a magnetic body like
Bteel and iron, and what is known as its magnetism becomes
an additional proof of the presence and activity of its elec-
tricity, and strengthens the probability that the globe is
1 I. C 56, 57, 60a, 60, 64, 73, 75, 81, 82. 2 I. C 6871.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 159
YI. A I.
itself the originator of thunderstorms and of all other elec-
trical phenomena known to occur in connection with it. 1
That the separated agencies composing this electricity
should be in constant motion in the magnetic field or orb,
from the equator towards the poles, is what is to be
expected from the analogy of the action of the lines of
force of magnets ; hence, in the field of the earth-magnet,
which we know also to be a conductor, we have manifesta-
tions of motion (rendered irregular by induction and geolo-
gical causes) in the shape of earth currents. 2
The polar accumulations of electricity thus formed would
influence by their powers of attraction and repulsion other
electricities similarly accumulated, within their range or
field ; 3 and this would explain the attraction of the earth's
poles on those of other magnets.
To the same fact of dense accumulation of electricity at,
or near, the magnetic and terrestrial poles, coupled with
the general absence of rain-clouds thereat, would be attri-
buted the manifestations of silent continuous discharges,
or leaks of electricity, in the polar regions, seen under the
form of aurorse. 4
And it is conceivable that the electricities, in their
motions through or over the earth towards the poles, are
occasionally forced by obstructions, due to geological con-
ditions, to accumulate for a time at certain places on the
surface; "and when this should occur in regions where
clouds and rainfall were frequently present, the necessary
conditions for the development of thunderstorms would
apparently be obtained. 5
Lastly, if the occasional irregular accumulations should
occur in certain portions of the earth's crust (generally not
very far distant from the sea), adjacent to, but insulated
from, each other, and below, though not far removed from,
the surface, and especially in regions where clouds and
1 I. C 110; G22. 2 I. Ce. 3 V. A a.
* I. C g. I. G 25. 5 I. C 1517, 34. I. D 11, 15, 18.
160 LIGHTNING.
VI. B .
rainfall were habitually absent, as in Chili and Lower
Peru, l there would appear to be possible causes for the
occurrence of earth explosions, manifested by earthquakes, 2
and their frequent volcanic accompaniments ; 3 it being
borne in mind that these convulsions have frequently been
found to coincide in time with magnetic fluctuations, and
that eruptions are constantly associated with lightning.
Taking, then, into account all the circumstances of the
two hypotheses concerning the function of the earth in the
terrestrial condenser, the one assuming that the clouds
originate thunderstorm electricity, and that the earth con-
denses it, and the other, that the earth originates this
electricity, and that the clouds condense it the latter
appears the more reasonable of the two. 4
We shall, it is hoped, see later on in this treatise, whilst
discussing the subject of leaks, that faith in the idea that
the earth's surface is the collecting plate of the terrestrial
condenser considerably facilitates the task of devising
practical measures for attempting to prevent the occurrence
of thunderbolts. 5
(B.) THE THEORY OF DESCENDING LIGHTNING.
One great reason for the assumption that the clouds are
the originators of the electricity of thunderstorms has pro-
bably been another assumption, and one apparently of
nearly universal acceptance, viz. that lightning strikes the
earth from above. 6
We propose to examine this theory, first, from the point
of view of fact ; and secondly, from that of electrical law-
() Facts regarding Descending Lightning.
Lightning appears to be an act, or manifestation, too
vivid and instantaneous to permit of the eye doing more
i I. G 23, 24, 28. 2 I. C k; G 22. I. C f.
* I. C 4. 5 VII. G c. I. D 1, 12, 14, 16. II. E 35.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 161
VI. B a.
than merely noting its existence. It seems quite impos-
sible, from sight, to say positively whether lightning as-
cends or descends, or has any motion at all. It would
probably be in strict accordance with reality to say that a
luminous rift or crack suddenly appears and disappears in
the gloomy atmosphere before the brain has time to inform
the mind of anything more than these bare facts. 1
As regards the traces lightning leaves behind it, the
writer has as yet been unable to meet with any single
record tending to prove that a stroke of lightning had
acted as a downward force.
The circumstances, however, of the strokes recorded in
the following eighteen incidents in Chapter III., tend to
show, more or less strongly, that in each case the action
of the explosion was upwards, viz. :
Nos. 5,
25,
103,
11,
26,
112,
12,
29,
124,
15,
40,
137,
16,
51,
173,
24,
62,
197.
In No. 5 the evidence of the column of water shot up-
wards into the air is remarkable.
In Nos. 11, 12, and 62, stones were thrown to distances
of 50, 55, 60, and 400 yards, the stones thrown 50 and 60
yards weighing respectively 70 and 336 Ibs. ; in No. 112 a
piece of wood 10 feet long was hurled to a distance of 50
yards ; in No. 197 the roof of a shed was projected more
than 100 yards ; and in No. 16 a timber spire of a church
was thrown to some distance.
Can we reconcile these circumstances with the idea of a
force acting from above ? From the weights and sizes of
the bodies, and the distances to which they were propelled,
it seems clear that the force must have been upwards.
1 I. D 8, 28, 29. J
162 LIGHTNING.
VI. B a.
The usual explanation of any great uplifting force mani-
fested by a lightning explosion appears to be that the
place struck must have contained more or less moisture,
the sudden conversion of which into steam by the intense
heat of the stroke has caused the effects in question. 1
But this is entirely a supposition ; and certainly, in the
instances above quoted, there is no record of the presence
of moisture.
It is of course possible that the sap in trees may become
thus transformed into vapour ; but it is difficult to under-
stand how the interior of a flagstaff or of a stone wall
could contain moisture to any extent.
Such a theory would moreover appear to involve the
occasional rending of the ground in cases where lightning
is supposed to "make good earth," i.e. to strike moist
ground ; but such results never appear to occur in these
instances.
In No. 15, the fact of the horses' hair being burnt on
the legs and under the bolly is noteworthy.
Lord Mahon, a distinguished physicist, 2 in a report at
the time on this case to the Royal Society, considered it to
be a return stroke, but Arago says that it showed ' ' unde-
deniably the principal effects of an ordinary stroke of
lightning." 3
In Nos. 16, 24, 51, and 173, there is clear evidence of
an uprooting force ; and in No. 51 we are informed in Sir
William Snow Harris's own words, that the clock-room
floor was left " as if blown up by gunpowder."
Nos. 25, 26, 29, and 124, appear to be almost as direct
evidences of the upward exertion of the force as it is pos-
sible to obtain.
Nos. 40, 103, and 137, also furnish, in their cases re-
spectively, fair grounds for belief in the existence of a
similar force.
It may perhaps be doubted whether these few instances
i I. D 44. 2 II. A 28. a VII. F c.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 163
VI. B a.
we have quoted are by themselves sufficient vouchers for
the existence of a force in lightning strokes invariably acting
upwards ; but it is extremely probable that the popular
belief to the contrary must have tended to prevent any
detailed examination of the traces of thunderbolts by the
light of this theory, the result of which belief has been
that, as a rule, the most meagre details are given of the
action of the explosion, except where the effects were
shown on the building or person, and the particular points
of ground where the lightning was supposed to have dis-
persed have been but little noticed.
It may be mentioned that in only five of the cases given,
viz. Nos. 24, 25, 26, 29, and 124, have the facts been pub-
lished expressly to denote the existence of ascending
lightning.
The 203 incidents mentioned in Chapter III. have been
collected without reference to any particular theory, and
merely in the hope of throwing light on the action of
lightning ; and it is now suggested that the reader should
experimentally peruse any one of them under the idea that
the lightning ascended, and sprang from the place (if such
is mentioned) where it was presumed to have entered the
ground, bearing in mind that the sequence of events re-
corded in the column of results would usually be inverted
(the description employed by the authority for the incident
having generally been adopted), and would always com-
mence at the ground, and thence proceed to the topmost
feature of the construction or object under consideration.
We venture to think tjiat the result will be that nothing
will be found in the facts related that is in disaccordance
with the theory of ascending lightning.
We will now consider the question from a mechanical
point of view, in connection with the striking of the points
of lightning rods by lightning.
The mechanical force present in lightning is supposed
to descend from above, to alight on the top of the unstayed
projecting slender metal terminal rod (say inch to 1 inch
164 LIGHTNING.
VI. B a.
in diameter, and 3 to 30 feet 1 nigh) of a presumably
efficient lightning conductor " making good earth," then
to proceed down it to earth, all without effecting any
mechanical injury ; and, in most cases, only, at the utmost,
to manifest its presence by fusing a small portion off the
point of the terminal.
But if this enormous force really does strike in this way,
surely it ought either to break off the terminal at its
junction with the part of the rod that is fixed to the wall,
or to knock the whole conductor down and to tear the hold-
fasts out of the wall.
It may be said that the rod being of metal disperses the
discharge by affording it an easy electrical passage to the
ground, and thus keeps itself uninjured.
Allowing, for argument's sake, that this is the case, we
may still ask what becomes of the mechanical force with
which the lightning arrives at the rod ? 2
There is apparently no electrical law by which conduc-
tors of electricity may receive a blow directed at them from
the outside without feeling its effects, by reason of this
blow having been itself actuated by electricity.
Now take the case of the same efficiently erected rod
under the idea of its receiving from the ground the elec-
tricity that actuates the blow. The circumstances are
changed. The rod does not receive the blow, but transmits
it : the reaction is on the ground ; and there is much less
reason why the slender unsupported terminal should be
broken, or why it should show any manifestation of the
thunderbolt's passage beyond traces of the intense heat it
must inevitably be subjected to when the discharge is on
the point of leaving it and becoming lightning.
Incidents Nos. 6, 8, 22, 56, 64, 66, 78, 79, 89, 92, and
156, are instances of lightning rods being struck and
receiving no material injury.
1 II. C 2, 3, 16, 23, 24, 48-50. IV. 1, 15, 16, 19, 2124, 2628,
30, 32, 35, 37, 41, 42. 2 yjj C 14- VI1I> Q j.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 165
VI. Bi.
(b) Descending Lightning from the Aspect of Electrical Law.
As to the scientific side of the question, doubtless one of
the reasons for maintaining th lightning usually descends
to the earth, has arisen from the fact that the electricity
on the earth's surface during fair weather has been
found to be usually of a negative kind ; l hence it has
been inferred that the same holds good during thunder
weather, and that the electricity of the clouds is then of
a positive nature, and that on analogy from the hypothesis
that a current traverses a conductor in the direction from
positive to negative charge, the direction of the lightning
discharge would generally be from the clouds to the earth. 2
Premising that we appear to have at present no definite
knowledge of the nature of the electricity resident during
thunderstorms on the earth or in the clouds (except that,
from the fact of explosions occurring between clouds, it is
evident that they may possess either kind of charge), the
above reason would seem principally to fail owing to the
obvious fact that lightning strokes, and electric sparks
generally, are evidences of explosion and not of current. 3
There is apparently no ground for assuming that the
action of an explosion follows the same law as that of a
current. 4
On the contrary, inasmuch as the scene of the one is
formed by bodies which have an exactly contrary influence
to those which form the scene of the other, it is only
reasonable to presume that the action of the one is also
very different from that of the other. 5
This hypothesis is strengthened by the fact that, in all
lightning explosions, the course of the discharge through
any metals that happen to be in the dielectric does not follow
the longest dimension of these metals, as it would if they
were conducting it like a current, but simply utilises as
i I. C 5. 2 I. D 12. II. C 43.
s LA 27; D 11, 16. V. A 13, 17, 30. 4 I. A 27.
5 V. A 13, 17. VI. D a.
166 LIGHTNING.
VI. B I.
stepping-stones such portions of them as happen to lie in
its path of least restraint to the condensing cloud's elec-
tricity, and leaps over any intervals occurring between
them ; and their influence on the discharge appears to have
exactly the same result as if they attracted it. 1
In the case of an electric spark leaping across a small
gap in a conductor, through which a strong current is
passing, the electricity is certainly brought to the edges
of the gap on each side, by means of the current ; but
there the work of the current ends, and what makes the
spark pass across is the formation of a condenser, and the
explosion of it resulting from the potential accumulated
on either side of the gap. 2
In the case of the lightning electric spark we have two
electricities, positive and negative, lying respectively on
either side of the great gap formed by the atmosphere.
The combined force of the two potentials has accumulated
to that stage where the capacity of the gap is no longer
able to restrain their fierce embrace ; but there is no
reason for supposing that positive has at this time more
attraction for negative than negative has for positive. 3
The conclusion, then, seems irresistible that, if there is
any element of time in the case at all, the lightning spark
leaves the two plates, the earth and the clouds, simul-
taneously, and coalesces half-way between; and this would
result in an invariable upward direction of the stroke im-
mediately above the surface of the ground. 4
Probably mythological traditions have had a consider-
able share in the formation of the belief that thunderbolts
strike the earth from the skies.
It is submitted, then, that the idea of the clouds being
the originators of thunderstorm electricity is devoid of
foundation so far as it rests on the theory that lightning
descends.
1 I. E 2, 6, 912. VI. D a. 2 V. A 30.
3 I. D 10, 13, 15. * I. C 39 ; D 7, 9, 10, 12, 14.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 167
VI. C.
(C.) THE OTJTLINE OF THE TERRESTRIAL PLATE.
Independently of the question whether the collecting
plate of the terrestrial condenser is formed by the earth or
the clouds, it is of importance that the exact outline of the
terrestrial plate should be determined ; for it is impossible
to deal satisfactorily with the subject of protecting life and
property from the ravages of thunderbolts until a definite
opinion has been formed on this point.
The theory on it of most recent acceptance appears to be
this, viz. the outline of the terrestrial plate is the upper-
most surface of the most collective stratum of the earth's
crust. 1
By this theory it follows that the rocks and less collective
portions of the earth's surface overlying this more moist
and collective stratum, form, equally with the air, parts of
the terrestrial dielectric. 3
Since, however, those portions of the earth's crust which
are not actually rock, and are consequently more liable to
receive moisture, e.g. earth, clay, loam, and sand, are
merely disintegrated rock, it is evident that all portions of
the earth's crust are allied in physical composition more
nearly to each other than to air, and that, therefore,
cceteris paribus, the actual rocks are the less likely to become
electrically separated from their moister earthy surround-
ings and to join the air in forming the dielectric of the
condenser ; and especially so when it is borne in mind that
stones and rocks can have but little inductive capacity. 3
Assuming, however, that the rocks on the earth's surface
may actually have inductive capacity sumcient to form part
of the dielectric of a condenser, it is certain that their
restraining power would be considerably less than that of
the air, and, by so much as would be due to that fact,
would facilitate discharge from the collecting plate below
them. 4
1 I. C 47, 48. II. D 44. 2 V. A 26^29.
3 VI. D a. * VI. D a.
168 LIGHTNING.
VI. C.
Rocky masses overlying moist strata would thus rather
encourage discharge ; and in the open country these strata
thus overlaid ought not infrequently to be the scenes
of thunderbolts ; and as we know from experience that
the action of explosion passing through substances of
the same nature as rocks, i.e. stone spires and walls, is
of a mechanically expansive, rending nature, it would
follow that sometimes, during thunderstorms, rocky strata
would be rent in pieces, mountains would be uprooted,
houses and even towns would be thrown down ; and the
effects of thunderbolts would, in fact, occasionally resemble
those of earthquakes.
But is this the case ? Do not our records tell us in the
first place that, as a rule, according to the generally
adopted form of expression, " lightning seeks good earth?" l
And what is this but telling us, in other words, that
discharges do not generally occur at rocky surfaces at all,
wherever moist surfaces are adjacent, and other things are
equal ? 2
And, in the second place, even at the rocky summits of
high mountains, where the facilitating element of great
elevation so overpowers the restraining one due to the
rocky surface that thunderbolts are not uncommon, do we
ever hear of crags and peaks being torn asunder by light-
ing? 3
But the stone walls of buildings being of the same
nature as rocks would facilitate explosion equally, and the
massive stone walls and arches of powder magazines ought
to be sources of danger to the powder, whilst the brick and
stone walls of dwelling-houses would tend to bring destruc-
tion rather than protection to their inmates.
The presence of rain during thunderstorms, so far as it
would affect the question, would appear to be entirely
against the theory of the rocks on the surface forming part
of the terrestrial dielectric, since, during rainfall, it is
1 I. C 45. 2 VII. A d. 3 I. G 33, 41. VII. A g.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 169
VI. C.
obviously the surface of the earth that first, and in the
greatest amount, receives moisture, and some time must
necessarily elapse before any lower strata receive the access
of collectivity due to this cause. 1
The theory that the outline of the terrestrial plate is
formed by the uppermost surface of the more collective
stratum of the earth's crust, rather than by the actual
surface of the earth, appears to have originated from the
fact that lightning rods and the buildings to which they
were fixed, have occasionally been struck when the earth
connections of the rods have been sunk in dry ground. 2
It has apparently been reasoned from this that the
falling lightning, having been denied an outlet in moist
soil, has reacted injuriously on the rod and the building,
and that it is imperatively necessary, in order that an easy
passage to the earth's great reservoir of electricity may be
afforded to the lightning, that the earth connections of all
lightning rods should be rooted in the more moist ground,
which is presumed generally to underlie the dry stratum
nearest the surface. 3
This conception of the cause of the injury to the rods
and buildings in question appears to rest on the idea of
lightning striking the earth from above, and to stand or
fall with that idea ; * but we hope to show, later on, that
a much more simple and natural cause can be produced to
explain the fact of injuries to lightning rods that are not
in good connection with the earth. 5
On the whole, then, the theory we have been considering
appears to have no good foundation, and does not prevent
the natural and primd facie view of the question being taken.
This view is clearly that the uppermost surface of the
globe, however such surface may be formed, and whether
by natural or by artificial substances, constitutes the out-
line of the terrestrial plate. 6
i II. D 44. 2 II. D 47.
3 II. D 21, 22, 49, 64. II. G 48, 52. * VI. B b.
5 VII. B/ VIII. B a. 6 I. A 24 ; C 46, 51. V. A 2629.
I
170 LIGHTNING.
VI. D.
This theory will, it is submitted, be found to harmonize
with experience regarding the action of lightning ; and it
is difficult to see what other hypothesis as to the outline of
the terrestrial plate would do so.
(D.) THE INFLUENCES OF THE MATERIALS COMPOSING THE
TERRESTRIAL CONDENSER.
Having now discussed the functions fulfilled by the earth
and by its surface in the economy of the terrestrial condenser,
it will be convenient to deal with the relative powers of the
various substances, natural and artificial, forming the prin-
cipal constituents of this surface (and of the condenser
generally) that tend to influence the collection of charge
and the occurrence of discharge. 1
The following table, compiled from the works of eminent
authorities, and as the result of general research, gives the
more important substances in what is deemed to be the
approximate order of their relative influences ; 2 it must
not, however, be considered as other than an imperfect one,
for there is, except as regards metals, very little accurate
information in existence on the subject.
Substances which are not usually in a position to affect
the terrestrial condenser in any important degree, in regard
to life or property, are purposely omitted.
1 V. A b ; B 79. 2 I. A 26 ; B 116.
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lly when in the open air),
le, sheep, dogs, pigs, &c. .
standing corn, grass, new-
ds, foliage generally . . y
, huts, barns, fences, rafters \
rs, doors, shutters, windows,
agstaffs, ts, ships, ships'
rniture, bsteads, walking j
iages and ts, verandahs,
osts .
spSpSOs&s
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Jf1f M 5f||
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B 0^2 0^0 JQ &00^ 3
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Surface of
eriodically o
graphic "bad
Rocky surf
building and
lime, mortar,
porcelain
Straw (
paper, he
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noiso^dxg;
jo
174 LIGHTNING.
VI. D I; Etf.
(J) Remarks on the Table.
Some kinds of trees and woods probably belong to
Group III.
There appears to be very little precise information ob-
tainable as to the relative influences of the building
materials, comprised under the heads of " Wood," " Dry
Earth," "Koekand Stone," "Clay Manufactures," and
" Dried Vegetable Substances."
In fact, there is undoubtedly scope for useful experiment
in determining accurately the relative influences of the
whole of the substances in Groups II. and III. ; for it
would manifestly be advisable to know the particular
materials best adapted for the construction of buildings *
needing special protection against lightning strokes, and also
the kinds of soil best suited as sites for such buildings. 2
As regards the influence of the metals, it can be de-
duced from the table that iron is 240 times more collective
of charge and facilitative to explosion than the most
collective non-metallic substance, 533,000 times more
so than sea water, 7,500,000 times more so than spring
water, rain r snow, hail, ice, human beings, animals,
vegetation, wood, clouds, fog, earth, sand, shingle,
rock, stone, brick, earthenware, straw, cotton, linen,
paper, hemp, wool, silk, leather, and bone, and
340,000,000,000,000,000,000 times more so than air,
asphalte, and glass ; and we gain from these figures some
idea of the enormous power possessed by metals relatively
to non-metallic substances for influencing lightning dis-
charges. 3
(E.) THE DISCHARGE OF THE TERRESTRIAL CONDENSER.
(a) The various forms of Terrestrial JZlectric Discharge.
We now come to the vital question of the discharge
of the terrestrial condenser ; 4 and so far as our present
i II. E 20, 21 ; G 43. 2 VII. A. 3 I. E 112.
* Y. A 1215, 3032; B 1012, 21.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 176
VI. E a.
state of knowledge enables us to judge, the following are
the forms in which it occurs, viz. :
1. A thunderbolt, or an explosion between the earth and
the clouds, through the intermediate air, constituting an
explosion of the terrestrial condenser. 1
2. A cloud explosion, or an explosion of a condenser
formed by two separate clouds, through the intervening
air. 2
3. A terrestrial return stroke, or a discharge back into
the earth from its surface, induced either by a thunderbolt
or by a cloud explosion. 3
4. A terrestrial leak, or an escape of electricity through
the air, between the earth and the clouds. 4
It is with the thunderbolt that we are mainly concerned,
but the actions of the other three forms of discharge are so
closely connected with it that their study cannot well be
dissociated from it ; and they are of great value in assist-
ing us to form a true idea of its exact nature, and of the
best means of preventing it.
We will now refer to the principal manifestations by
which these various forms of discharge display their
presence.
We know that both thunderbolts and cloud explosions
are generally manifested by what are known as thunder
and lightning ; 5 return strokes are necessarily without
atmospheric manifestation, and show themselves chiefly in
the forms of shocks and currents ; 8 whilst leaks are
occasionally visible in the form of auroree, 7 heat or sheet
lightnings, 8 and St. Elmo's fires. 9
On examining the conditions of these phenomena, it will
be found that the element essential to the luminous
appearances connected with them is the air.
1 I. D 1, 2, 3, 11. V. A 13, 30 ; B 10, 11, 21. VI. A a.
I. D 16. V. A 30. 3 I. D 63. V. A 14, 31 ; B e.
* I. A 16. 11.011. V. A 15, 32; B 15 20, 21.
I. D 16. I. D 53, 6670.
7 I. C 78. I. D 4, 20. I. C h.
176 LIGHTNING.
VI. E I.
The visible token in the air of explosions is lightning,
and of leaks, light.
We are taught that lightning is the appearance of in-
candescent matter suspended in the air. 1 It cannot, there-
fore, be the proper term with which to describe the explo-
sion itself, nor can it be correct to apply the term to that
portion of a thunderbolt explosion which passes through
any other substance than air, e.g. through walls, metals, or
human beings.
In England the word lightning is generally used to ex-
press promiscuously thunderbolt explosions, cloud explo-
sions, leaks shown by " heat lightnings," and the luminous
phenomena attendant on these discharges.
In France, however, the term lafoudre, or thunderbolt, is
always used in designating a lightning discharge with the
earth, 2 whilst V eclair expresses the lightning itself.
The term thunderbolt has the confirmation of lexicology
and the sanction of antiquity ; and it evidently expresses
conveniently the distinction between the harmless lightning
that plays among the clouds, and the terrible shafts that
visit the earth. 3
(1} The Rationale of Thunderbolts.
Explosion is evidence of work, 4 and, as we have seen,
work is, electrically speaking, the product of quantity and
potential. 5
There may, however, be, on the one hand, immense
quantity present, and yet nowhere sufficient potential to
determine explosion ; and, on the other hand, an enormous
potential may be developed, yet with such minute quantity
that again the combination is inadequate to produce
explosion.
In the latter case, however, discharge might probably
ensue in another form, viz. that of a leak. 6
1 I. D 5, 6. 2 I. D 3, 11, 18.
3 I. D 1, 2. 4 V. A 12.
5 V. Ba. II. C 11. V. A 32; B 17, 18.
CONSTITUTION OF THE TERRESTRIAL CONDENSER. 177
VI. E I.
A terrestrial explosion, or thunderbolt, requires, there-
fore, for its formation two distinct agencies, viz. sufficient
quantity, and sufficient potential ; and it only occurs
at a point on the earth's surface when the combined
effect of the quantity and potential accumulated thereat,
and of the reciprocal quantity and potential accumulated
on the under- surf ace of the clouds, is powerful enough
to overcome explosively the restraint of the intervening
air. 1
The quantity originates with the charge from unknown
causes acting from below, and the high potential is due to
the condensing influence of the clouds. 2
It is clear that the immediate cause of all discharge must
be charge. It is therefore to charge, and to all circum-
stances that tend to collect it, and to raise its potential,
that we must first direct our attention in investigating the
origin of thunderbolts.
Where lightning discharge is seen at the earth's surface,
there, it is obvious, that charge must, just before, have
existed. 3 To put the same fact in another form, it is only
at the spot where the charge that causes the lightning resides that
the latter can possibly " make earth."
This fact appears to have been constantly, almost
systematically, lost sight of ; but it must undoubtedly be at
the root of all inquiry as to the action of lightning on the
earth, and as to the best means of defending life and pro-
perty from its effects.
Of course, if we knew the original cause for the existence
in the earth of electricity, and the exact method in which
it collects itself at places on the surface, we should have
the best, and indeed only sure, foundation for our endea-
vours to prevent thunderbolt explosions ; but, as we have
already said, we know at present next to nothing of this
cause and method ; 4 so all that we can do is to make the
1 I. D 11, 17. V. B 11. 2 I. C 36. 3 V. B 11.
4 VI. A b.
i 3
178 LIGHTNING.
VI. E b.
most use possible of the facts and laws to be deduced from
the researches and experiments made by eminent men, 1
and to study the experience which, unfortunately, is con-
tinually accruing from the very disasters which we wish to
prevent. 2
Having settled then that the existence of charge or
electricity on the surface of the globe is the cause of light-
ning explosion, and being unable to account for the origin
of this electricity, our investigations must be essentially
devoted to the conditions that tend to affect its explosive-
ness. 3
1 I. 216, 19, 2124, 28> 31, 3235. II. C 26,.
a i. Q 1 _ 42 . III. 1203. 3 Y. B 12.
TIL A a.
CHAPTEE VII. THE ACTION OF THUNDER-
BOLTS.
(A) THE ELECTRICAL CONDITIONS OF THE EARTH'S SURFACE.
(a) The Accumulation of Electricity on the Earth's Surface.
ALTHOUGH, as we have said, both quantity and potential
are necessary in order to produce explosion, still the main
and immediate element in its production is necessarily
potential; 1 it is therefore to the circumstances of the terres-
trial condenser affecting the accumulation of potential, that
we must principally direct our attention ; and, first, we
have to consider the conditions of the natural surface of the
earth in this respect.
The earth collecting plate receives its charge, by a
method unknown to us, from the source in the interior.
This charging process goes on for a certain period of
time, and presumably with some uniformity of action.
The area thus charged, limited probably by the geo-
logical conditions of the earth's crust below it, usually
consists of surfaces composed of substances of various
degrees of influence. 2
The quicker collecting of these substances would, cceterit
paribus, collect their full measure of any limited quantity
of electricity with which the whole area might simul-
taneously commence to be charged, in a proportionally
shorter time than would the substances of lesser collec-
tivity. 3
1 V. B 4, 11. * VI. D a. . V. A 9, 10, 19, 20.
180 LIGHTNING.
YII. A &.
Hence, if tlie area should be charged from a source of
unlimited electricity, the more collective substances or
surfaces would, in any given time whilst the charging
process lasted, collect the greater charge, i.e. would
(capacity being unaltered) attain to a higher potential. 1
Now the earth is undoubtedly a practically unlimited
source of electricity, 2 and it may be presumed that, just
previous to a thunderstorm, its surface is charged in such
a .manner that electricity is continuously accruing thereon,
though perhaps at a rate almost imperceptible.
It follows then that the more collective portions of this
surface will collect, in any given time during this charging,
the more electricity, and thus will obtain the higher
potential.
The various portions of the charged area being, previous
to a thunderstorm, in these relative states, would all accu-
mulate potential at a much greater rate as soon as a
thundercloud should begin to condense them ; 3 but these
accelerated rates would again vary (on the principle just
enunciated) in proportion to the different collective powers
of the surfaces.
The result is, therefore, that the more collective any
particular portion of the earth's surface may be, the more
will potential tend to accumulate thereat, and the more
likely will explosions be to spring therefrom. 4
(I) Surfaces of Water.
On referring to the Table of Influence, it will be seen
that water of all kinds is the most highly placed of all
natural collectors on the earth's surface, and that the sea
takes the precedence. 5
This points to the danger that all bodies on or near
1 V. B 1, 7, 12. 2 I. C 52, 53. 3 V. A 28.
* I. C 3745 ; E 6 ; G 3134, 39. II. D 54 ; G 28. VI. D a.
VII. A h. 5 VI. D .
THE ACTION OF THUNDERBOLTS. 181
VII. A b.
natural sheets of water, and especially ships on the sea,
are subject to during thunderstorms. 1
An additional element of risk would appear to attend on
vessels when they are in motion during such storms, since
it would evidently be possible for a vessel to proceed from
one explosively charged area to another, or to keep
company, more or less, with a highly condensing cloud in
its course above the ocean, either of which circumstances
would tend to cause the ship to be the scene of repeated
explosions. 2
There is, however, a very important aspect of large col-
lective surfaces to be noticed, viz. the capacity of their
dielectrics, qua area ; for the action of this area would,
proportionally to its extent, reduce the probability of
potential accumulating at any particular portion of it. 3
The immense uniformly collective area of the ocean
would, therefore, by increasing the capacity tend to
decrease the potential, of any charge arising at its surface
from below, and this would constitute a source of protec-
tion to ships ; though, on the other hand, it would give
scope for the presence of a charge in greater quantity.
Sheets of water, such as small rivers, streams, pools, and
ponds, would probably be the natural surfaces of all others
that would most assist in bringing about explosion, pro-
vided their areas were not too limited to furnish a sufficient
quantity of electricity ; and, as a matter of fact, we know
that when lightning does occur between the earth and the
clouds, it generally " makes earth," or appears when close
to the earth, at pools and places where moisture abounds ; 4
and this (as we have before submitted) is only another
way of expressing the fact that the charges which caused
the lightning accumulated at these places, and that from
them the lightning sprang.
1 II. E 1. VII. C 2. 2 VII. C 11. 3 V. B 1, 7, 12.
4 I. C 3739, 43, 45; E 6; G 39. II. D 43, 49, 54; G 48.
VII. A h.
182 LIGHTNING.
VII. A C d.
(c) Moist Earth.
Moist earth, or telegraphic "good earth," such as con-
stitutes the greater portion of the surface soil of England
in its ordinary state, is clearly, according to the views we
have advanced, somewhat receptive of charge. 1
It becomes evident then that the best positions for
erecting buildings, so far as their defence from the action
of thunderbolts is concerned, are away from the banks of
rivers and lakes, and from the vicinity of pools, streams,
and moisture generally; that the better drained and the
drier the ground is around the buildings, the better ; and
that the theory of moist earth being necessary in the
neighbourhood of a building for the purpose of defending
it from the effects of lightning is exactly contrary to the
real requirements of the case. 2
Vegetation, which per se is more collective than moist
earth, probably increases the collectivity of the ground ; 3
and this idea accords with the apparent fact of the greater
frequency with which thunderbolts occur in the fields and
in the open country than in the towns. 4
As in the case of the sea, the potential of the charge on
moist earth would tend to vary inversely as the extent of
collective area over which it was spread, so that a com-
paratively small portion of moist earth circumscribed by rock
or dry earth would be all the more dangerous. 5
(d) Rocky and Dry Surfaces.
From what has been stated, it is clear that rock and dry
earth, being less collective than ordinary moist earth,
would, in any given time, collect a smaller charge, i.e.
would not attain so high a potential. 6 Hence, such sur-
faces would tend to be sources of protection, and a house
built on a rocky or very dry surface, or at a distance from
1 VI. D a. 2 II. D 7, 22, 26, 28, 3d, 43, 49, 63, 54 ; G 52.
a VI. D a. * II. G 1921, 35, 36. 5 VII. A h.
6 VI. D a. VII. A h.
THE ACTION OF THUNDERBOLTS. 183
VII. A 9.
moisture, ought to be, ipso facto, less liable to be struck by
lightning.
This view is fortified by the experience, already cited,
that lightning is found, as a rule, to seek moisture ; l for
this clearly implies that it avoids, by preference, places
where moisture does not abound, viz. rocky and dry
surfaces.
By rocky surfaces we mean those formed of the bare
rock, and not merely rocky sites ; for it will frequently be
found that rocky sites are more or less overlaid in places
by thin coverings of soil or sod, and places so covered
would not come within the category of rocky surfaces. 2
Even coverings of snow and ice on otherwise rocky sur-
faces, as e.g. Alpine summits, would doubtless completely
alter their character, and would make them more suscep-
tible of collecting charge than the bare rock ; and there is
reason to believe that, in most cases where explosions
spring from rocky sites, these sites have been covered with
some extraneous substance tending to faciliate the accumu-
lation of electricity. 3
The curious "fulgurites" that is occasionally produced
where the ground is struck by lightning is an apparent
instance of explosion occurring from a slowly collective
surface ; but without a full knowledge of all the concomitant
circumstances in cases of " fulgurites," it would be difficult
to form an accurate opinion as to its cause. 4
On the same principle as that already mentioned in
regard to collective surfaces, rocky, dry, and all slowly
collective or insulative surfaces would be proportionally
less influenced by the condensing action of thunderclouds.
(e) Paved Surface*.
From the consideration of surfaces naturally rocky we
are led to that of surfaces artificially BO, viz. stone pave-
ments. 5
1 VI. C. * III. 54. I. G 40, 41.
* I. D 39, 42, 43. * VI. D a. VII. A h.
184 LIGHTNING.
VII. A e.
Here we appear to have very similar conditions of slow
collectivity, though probably the thickness of the paving
would be an element in the question, since it cannot be
supposed that, in practice, however theoretically correct the
idea may be, a mere film of slowly collecting matter on the
earth's surface would have so much effect in preventing
explosion as a thicker stratum; for since the surface
receives its original charge from below, the thicker the
mass of slowly collecting substance immediately below the
surface should be, the farther would the bulk of this
charge be kept from it, and the less likelihood would there
be of its receiving any appreciable quantity of electricity.
In the case of ordinary well-laid stone nagging, there
would seem, to be good ground for presuming that the sur-
face would be proportionally less collective than if the soil
had not been covered at all.
Brick pavements would probably be more insulative
than stone, and asphalted ones more so than those of brick.
On the same principle we have reason to expect that a
layer of metal laid on the earth's surface could greatly
increase the collectivity of the plate thereat.
It is submitted that the paved surfaces abounding in cities
and towns, and especially close around buildings therein,
are among the causes that contribute to protect the build-
ings from thunderbolts. 1
The essential idea that we have been urging regarding
the influence of rocky and slowly collecting surfaces is that
the electricity derivable from the interior of the earth has
every reason to accumulate by preference in places of good
collectivity, and that even if slowly collecting surfaces do
become charged from below, they are only in a com-
paratively small degree condensed by the clouds; hence such
surfaces are the less likely to accumulate potential, and
consequently explosions are the less likely to spring from
them.
1 I. G 11, 35, 1921.
THE ACTION OF THUNDERBOLTS. 185
VII. Kfg.
(/) Surf aces formed by Railway Metals.
An artificial feature, partaking somewhat of the nature
of metal pavement, and appertaining largely to countries
where civilisation prevails, is the network of iron, formed
by the railway system. 1
Here we have a surface highly capable of accumulating
potential, qua its metal, 2 but of great capacity qua its
surface, 3 and thus in a condition somewhat analogous to
that of the ocean.
The influence of railways cannot, however, be
thoroughly discussed without taking into account a third
condition attached to them, viz. the leaks occasioned by
the angularities of their metals. The subject will there-
fore be dealt with again under the head of Terrestrial
Leakage. 4
(g] The Shape and Geological Formation of the Ground.
Turning now to the topographical feature of the
ground, 5 it is evident that the higher any place is above
the level of the sea, and, hence, the nearer to the clouds,
the less thick is its dielectric.
General elevation thus tends to reduce capacity, qud its
thickness, and therefore, cceterisparilus, to increase potential ;
hence it is a source of danger. 6
Table lands, mountain ranges, and watersheds generally,
would on this account be regions in which potential would
tend to accumulate, in preference to basins.
On the same principle, any feature of the ground
elevated above its surroundings, independently of its
general level, would be, qud that fact, a source of com-
parative danger, and the summits of mountains and hills
1 VII. A h. 2 VI. D a. 3 V. B 1, 7, 12.
4 VII. O d. 5 vil. A h.
6 I. D 17, 35. II. C 43 ; G 26. V. B 1, 7, 12.
186 LIGHTNING.
VII. A h.
would be places more exposed to risk than the sides and
valleys. 1
Lateral prominence of ground would also lead to
increased exposure to chances of condensation by a cloud
approaching, but not as yet arrived at, the zenith of the
place, in comparison with other portions of ground not
horizontally exposed in so great a degree.
The sides of hills and the sea coast are examples of this
condition of prominence.
The geological nature of the earth's crust at any place
would probably constitute a most important element
affecting the occurrence of charge on the surface. 2
So little, however, appears to be known of the relative
influences of the various kinds of rocks and geological
formations as regards terrestrial electricity, that there is
not much scope for enlargement on the subject ; 3 though
there is probably not much doubt that certain formations
favour the collection of electricity much more than do
others.
A thorough study of the earth's crust, with reference to
terrestrial electricity, and to the actual localities of thunder-
bolt explosions, would probably throw much light on many
points as to which we are at present in darkness, and
would materially assist in solving the problem of the cause
of the earth's electricity.
(A) Analysis of Incidents in regard to Conditions of Surface,
The following incidents in Chapter III. contain more or
less allusion to conditions of surface :
Sea (except cases of Ships}.
tfos. 44, 83, 96, 117, 123, 179, 180.
Rivers.
Nos. 15, 125, 127, 137, 181.
i I. Q 33, 40, 41. I. C 41 ; G 30; VII. A A. ' VI. D b.
THE ACTION OF THUNDERBOLTS. 187
VII. B a.
Lakes.
Nos. 30, 31, 85.
Wells, Pools, and Streams.
Nos. 49, 82, 103, 155.
Dry Earth, Sand, or Rock.
Nos. 22,
86,
117, 156,
44,
87,
128, 157,
64,
89,
131, 178,
65,
91,
147, 179.
64,
103,
155,
Other natures of Soil or Ground.
Nos. 10,
117, 168,
54,
118, 176,
56,
129, 182,
90,
147, 202,
116,
161, 203.
Charcoal Trenches.
No. 47.
Pavements.
Nos. 24, 112, 181, 183, 192, 203.
Railways.
Nos. 88, 98, 151, 198.
Elevated or Exposed Ground. 1
Nos. 4,
95,
117,
155,
55,
108,
128,
156,
79,
116,
H7,
181.
94,
Valleys or Low Ground.
Nos. 3, 54, 59, 203.
(B) DETAILS OF THUNDERBOLT ACTION.
(a) Classification of objects on the Earth's Surface.
"We now come to the consideration of the principal
objects, not forming integral portions of the earth, met
* VII. B e.
188 LIGHTNING.
VII. B a.
with on its surface, such as the artificial features presented
by buildings, ships, and constructions of all kinds, and the
extraneous features formed by natural objects, such as
human beings, animals, and trees.
In Chapter VI., Section C, we have submitted that the
uppermost surface of the globe, whether such surface is
formed by natural or by artificial features, constitutes the
outline of the terrestrial plate.
Under this aspect, it is evident that the sides and upper
surfaces of the artificial and extraneous objects we are now
dealing with, form, wherever these are isolated features on
the natural surface of the earth, portions of the earth's
collecting plate.
An important element, however, comes into play with
these objects, and that is their amount of electrical con-
nection with the earth's natural surface.
If this connection be good, then the object under con-
sideration, qud its exterior sides and surfaces, takes an
active share in the general collecting plate, and constitutes
what may, perhaps, conveniently be called a local col-
lecting plate, or local plate.
If, however, this electrical connection should not exist,
or should be bad, then the outer surfaces of the object,
whatever may be their collectivity, are, like the rocky and
dry surfaces considered in the last section, merely passive
portions of the general collecting plate ; but, unlike the
rocky surfaces, the objects we are now treating of
present, as a rule, when taking only a passive share in the
earth's collecting plate, a special feature which causes
them to play an active part in another sphere of influence.
This special feature consists in the more or less vertical
surfaces presented by the sides of buildings and other
objects, which surf aces must materially influence, according
to their powers of restraint, the dielectric immediately over
the portions of the natural surface of the earth lying close
outside the bases of these vertical sides. 1
i V. A 23, 29.
THE ACTION OF THUNDERBOLTS. 189
YIL B I.
In fact, these sides necessarily form local dielectrics to
the ground immediately adjacent to them, and the whole
of the outer surfaces of the building or object, so long as
their direction with regard to the ground in question is
at all inclined upward, must, since the direction of a con-
densing cloud may be at almost any angle above a hori-
zontal plane through any part of the building, take a
greater or less share in these local dielectrics according
to the circumstances of the case ; and indeed, an instance
is on record of a thundercloud having been even below the
level of a building struck through its agency. 1
All the objects, then, to be met with on the earth's
natural surface, are capable of being grouped either as
local plates or as local dielectrics, according as they are,
or are not, electrically connected to the ground. 2
(b) Electrical Connection.
It becomes necessary now to consider what constitutes
good electrical connection.
Good electrical connection between two articles or sub-
stances means the existence of such intimate contact
between them, that electricity freely distributes itself
between the two, without meeting obstruction at the points
of contact.
This condition can only apply between two articles or
substances which are themselves good collectors or con-
ductors, and cannot be said to exist in the case where
either body is a slow collector, still less where one of
them is an insulator. 3
Electrical connection is not the same as mechanical
contact, for even when the latter exists between two
articles of the same metal, considerable hindrance to
electrical distribution is frequently caused by the slight
film of air existing at the apparent contact ; and to make
1 III. 4. 2 VII. C 1518. 3 VI. D a.
190 LIGHTNING.
VII. B C.
good electrical connection between an object and the
ground, the presence of some degree of moisture appears
to be generally requisite, the action of which seems, by
means of some kind of electrolytic action, to render contact
more electrically perfect.
For a collector, then, to be in good electrical connection
with the earth, it would generally be necessary that the
surface crust should be more or less in a moist state, and
that the collector should either be itself in close contact
with this crust, or should be joined thereto by some form
of continuous metal, this metal being itself incorporated
with the collector at one end, and buried in the ground at
the other.
No other substance than metal would seem to provide
efficient connection between the earth and a metal or
collector separated from it.
It is then assumed, as a broad rule, in the following
paragraphs, that an object not composed of collective
material, or, if a collector, not in contact with the surface
of the earth nor joined thereto by metal, is not electrically
connected to the ground, and consequently forms a local
dielectric ; whilst those collectors that are thus electrically
connected constitute local plates ; and by the term ' ' ground ' '
or " earth," the kind of ground, in its average state of
moisture, which forms the ordinary surface soil of England,
is intended. 1
(0) Explosive Action.
Explosive action necessarily follows the line of least
restraint between the points of explosion on the collecting
and condensing plates. 2
Experience shows, however, that in the terrestrial con-
denser it is quite impossible to foresee the exact direction
and path of this line ; and this is the less remarkable
when we consider that the plate formed by the cloud is
1 VI. P a. ' I. D 31, 32. V. A 30.
THE ACTION OF THUNDERBOLTS. 191
VII. B C.
always more or less in motion, and that the precise position
it will occupy over any particular building or place on the
earth's surface at the moment when potential has accumu-
lated to explosive point can obviously never be pre-
dicted. 1
The zigzag appearance of lightning is an undoubted
proof of the irregularity of the course of an explosion's
line of least restraint. Explosive action can only exist in
a restrainer or slight facilitator ; 2 and it always proceeds
through one of these substances, though this piercing
action may occasionally take a path coinciding with the
plane of contact between two dissimilar substances, as e.g.
over the exterior surface of a wall whilst piercing the film
of air in contact therewith. 3
The fundamental law concerning explosive action
appears to be that it springs from the collecting and con-
densing plates, and acts within the dielectric.
Explosion, therefore, affects terrestrial objects very dif-
ferently, according as they form local plates or local
dielectrics.
The chief manifestations of terrestrial explosive action
appear to be as follows, viz. :
1 . Spark or Lightning.
2. Heat.
3. Expansive or rending force.
4. Uplifting force.
5. Shock to animal systems. 4
Explosion, when passing through the air, is manifested
by lightning and heat ; and, when through other restrainers,
or through slight facilitators, by rending, uplifting, and
heat.
In the case of local plates, explosion only injures them
in the act of springing from or leaving them, and the
1 II. E 35. * V. A 22, 23. VI. D a.
3 II. G 33. * I. D 16, 37, 39, 40, 41, 4446, 53.
192 LIGHTNING.
VII. B o.
injury takes different forms according to the substance of
the plate. 1
Thus when metals form local plates, explosion frequently
fuses them at the exact places where it leaves them, where,
in fact, it is in contact with them in the form of great heat,
viz. lightning ; but it does not otherwise damage them. 2
In leaving human beings and animals it usually causes
a fatal shock to the system, accompanied by traces of
burning. 3
In leaving woodwork, it generally shatters the extremi-
ties, and occasionally sets it on fire. 4
In its action on local dielectrics, explosion is necessarily
more violent, and is accompanied by an uplifting force or
blow.
When it passes through metals forming local dielectrics,
it generally fuses them at the points where it enters, as
well as where it leaves them, at which points the character
of the explosion is necessarily influenced by the non-
metallic substances which it leaves and enters, respectively ;
but the bodies of the metals, except in the case of thin
wires, do not appear to be heated or otherwise materially
affected, a circumstance probably due to the great influence
possessed by metals for facilitating the passage of the
explosion when they are strong enough to resist its
mechanical shock; in other words, to the fact that they do not
afford sufficient time for the work of an explosion passing
through them to manifest itself in the form of heat. 5
Thin wires are occasionally recorded as having been
melted, such having doubtless at the time been considered
as the most obvious manner of accounting for their disap-
pearance ; but it would seem probable that the metal of
very small wires, e.g. bell wires, is of too small extent to
exercise much facilitating influence on the explosion, and
that they are usually disintegrated and dispersed by its
1 VI. Da. 2 I. D 36, 47. VII. C 3. VIII. C 9.
3 VII. C 8, 9. * VII. C 1 n, 6.
5 I. A 31 ; D 36, 47. VII. C 3. III. 27, 28.
THE ACTION OF THUNDERBOLTS. 193
VII. B e.
mechanical force or blow, 1 and the not infrequent action
of explosion in breaking in pieces slender lightning rods
not electrically connected to the ground, would appear to
confirm this view. 2
When human beings form local dielectrics, they must
experience, firstly, the blow from the explosion ; secondly,
the shock due to its passage through their bodies ; and
thirdly, the shock due from its contact on leaving them.*
When woodwork forms part of a local dielectric, ex-
plosion appears sometimes to shiver it, and at other times
to set it on fire. 4
Trees and woods probably differ from each other con-
siderably in their influence, and little seems to be known as
to their relative powers for collecting charge or for facili-
tating explosions. A portion of a construction made of one
kind of wood might act as a plate, whilst the same object
in the same position, made of another kind, might act as a
dielectric. 5
It is when passing through brick and stone, and through
all restrainers and slight facilitators, that an explosion
manifests itself most violently. It here exhibits a powerful
rending force, 6 which necessarily has a disastrous effect
on the buildings which experience it, and also an uplifting
force. 7
This latter force occasionally lifts heavy stones, and
transports them to considerable distances ; and the result
of the two forces is frequently not unlike that due to a
gunpowder explosion.
Church spires of stone, surmounted by metal work, and
containing within them much metal in different forms at
various elevated levels, are more especially apt to ex-
perience the rending force of thunderbolts. 8
When it is merely the exterior surface of a brick or
1 II. B 22. III. 18, 19, 52, 65, 67, 119. 2 VIII. C 5, 10.
3 VII. C 8. 4 VII. C 1 /*, 6. 6 II. G 33, 39. VI. D a, b.
6 I. D 45, 46. VII. C 1 TT, 14. 7 I. D 40. VI. B .
8 VII. C 1, a, *.
104 LIGHTNING.
VII. B d.
stone building that acts as a local dielectric, it is probable
that there is less scope for the display of this rending action,
since most of the expansive force would be dissipated in
the atmosphere.
Explosion occasionally ploughs a path horizontally along
the surface of the earth, for some distance from the place
whence it springs, before it utilises an object on the surface
in order to rise therefrom. 1
In our present state of knowledge it would probably be
quite impossible to give exhaustively all the various
manners in which explosive action is liable to act ; but,
from what has been submitted, it would appear certain
that the injury it effects on an object is as a rule far
greater when that object is a local dielectric than when it
is a local plate.
(d) Local Plates.
If a construction of wood, or of metal, or of any sub-
stance of good collectivity, should be electrically connec-
ted to the ground, the exterior surfaces would receive
charge therefrom, and would constitute a local plate.
A wooden or metal building, thus circumstanced, being
more collective than the surrounding surfaces, 2 would, on
the same principle as that already mentioned in the case of
two unequally collecting surfaces of ground, attain to a
higher potential; for the combined surfaces of such a
building would in any given time accumulate a greater
amount of electricity than an equal area of ground.
It is thus evident that a metal building is liable to form
a local plate of great accumulating power, 3 and that an
explosion is, cateris paribus, more likely to spring from
such a building than from the ground immediately around
it.
All metal constructions and objects, however, when
forming local plates, contain the element of leakage in a
* VII. C 13. 3 VI. Da. 3 I. E 3, 7, 9. VI. D b.
THE ACTION OF THUNDERBOLTS. 195
vn. B d.
greater or less degree ; and this element (which is treated
on hereafter in Section F *) probably exercises consider-
able influence in preventing explosions from them.
The comparative absence of leakage conditions in wooden
constructions renders it likely that, as local plates, they
are more dangerous than metal buildings. 2
We have now to consider brick and stone buildings
containing, on their walls or roofs, metal surfaces, such as
roof coverings, eaves gutters, rain-water pipes, finials,
vanes, and other articles, all electrically connected to the
ground. 3
These surfaces come into the same category as metal
buildings, and constitute local plates of more or less
importance in proportion to the surface of metal they
display ; and there is no reason for assuming that any
form they may possess such e.g. as long slender rods,
bands, tubes, or wire ropes, or that any direction these
may take, whether vertical or otherwise, in any way alters
their collecting power ; although this would, of course, be
affected by leakage, on the same principle as for metal
buildings.
It is clear that an explosion possesses more power to
injure a brick or stone building containing various metal
surfaces than one formed wholly of metal. 4
One element, however, in connection with metals gene-
rally, would have a great influence over explosion, viz.
their elevation above the ground; and this influence would
be present in all local plates.
Elevation would act as follows : In proportion to the
height of a local plate above the general surface of the
ground the thickness of the air dielectric would be dimin-
ished ; thus capacity is to the same amount reduced, and
(quantity being unaltered) potential becomes proportionally
increased. 5
1 VII. F c. 2 II. E 42. VII. C 1 t.
3 VII. 03. 4 I. E 2, 6, 10, 12. VII. C 3.
5 I. D 17, 35. II. G 26. V. B 1, 7, 12.
196 LIGHTNING.
VII. B 0.
Elevated metal in tlie form of a local plate is thus a
condition tending greatly to promote explosion. 1
Ships, when afloat, are well connected to the earth's
surface (formed by the sea) ; thus they generally constitute
local plates; and, for the same reasons connected with
leakage as mentioned in the cases of wooden and iron
buildings, wooden ships, would generally be more dange-
rous than iron ones. 3
The following objects would probably also be liable,
during thunderstorms, to form local plates, viz. :
1. Human beings and animals standing on the
ground in the open air. 3
2. Trees. 4
3. Flagstaff s and telegraph poles springing from
the ground. 5
It is evident that a construction or other object may
occasionally form partly a plate and partly a dielectric, as
e.g. when a metal surface on the lower part of a stone
building is electrically connected to the ground ; in this
case all the rest of the building, especially any part above
or adjacent to the metal surface or its connection to the
ground, is liable to constitute a local dielectric to the local
plates formed by the metal. 6
Local plates are also always liable to act accidentally as
local dielectrics to each other, or to adjacent portions of
ground to which they themselves are not electrically con-
nected. This condition will be more fully discussed after the
question of local dielectrics has been considered. 7
(e] Persons in the Open Air.
That human beings on the ground, in the open air,
when killed by lightning, do usually form local plates
seems almost certain from the following facts, viz. :
1 IT. G 43. VII. C 15, 16. VIII. C 6. 3 VII. C 2.
> VI. D a. VII. C 8, 9. 4 I. F 58. VII. Co. I. D 44.
5 VII. C 6. s VII. C 16. 7 VII. B g.
THE ACTION OF THUNDERBOLTS. 197
VII. B <?.
(1.) They, under the same circumstances, constantly
receive shocks from return strokes ; and this
would be impossible if at the time they had
formed local dielectrics. 1
(2.) If a person, ordinarily clad, and not standing
on an insulating stool, touches a charged con-
ductor in a laboratory, the charge escapes
through his body to earth ; which shows that
the leather soles of boots are not insulators. 2
It is thus tolerably clear that, as a rule, a person,
situated as above described, has been previously charged
on some part of the surface of the body by the ground ;
and that death ensues from the fearful shock given to
the delicate nervous organization of the human system
by the starting of a thunderbolt from the charged
surface.
It appears reasonable to infer that the upper and
more vital portions of the body, such as the regions of
the head and heart, are the particular parts that fatal
explosions usually spring from. 3
The charge that thus explosively leaves them has accumu-
lated, unconsciously to them, on the actual surface of their
bodies ; and the explosion pierces its way through the
slightly f acilitative substances, such as cotton, linen, flannel,
wool, cloth, silk, leather, felt, of which their clothes usually
consist, in the direction rendered least restraining by the
presence of metal in and among their clothes, and espe-
cially metal of a highly attractive nature, such as gold,
silver, and copper.
These clothes and metals must doubtless be looked upon
as local dielectrics, and the existence of the metals is
probably an element of vital importance, and constitutes
the last drop that overflows the electric bucket. 4
During thunderous weather in the country, it would
1 I. D 55, 56, 58. VII. C 8. VI. D a.
3 I. D59, 60. * I. E 11; F 15.
198 LIGHTNING.
VII. B/.
appear to be worth the while of everybody (and perhaps of
ladies in particular) to reckon up the amount of metal they
carry, in one form or another, about their persons before
they go on expeditions to places remote from accessible
buildings, whether they be walking, riding, or driving. 1
Of these occupations, riding would seem to be especially
dangerous, owing to the good electrical connections formed
by the horse's shoes, the horse's collectivity, and the ele-
vation of the rider. 3
We find, from the records of fatal thunderbolts, that the
traces most frequently left by them correspond closely with
the course of action on the part of explosions that has just
been suggested. Traces of burning are found on the
skin, doubtless where the explosion left it; clothes are
torn ; and watches more or less fused. 3
The fatal accident that occurred at Schelthorn, one of
the Bernese Alps, on the 21st June, 1865, when a young
English lady was the victim of a thunderbolt, is an
exceptionally distressing instance of the danger to which
persons in the open air are exposed to during thunderous
weather.
(/) Local Dielectrics.
The walls of buildings constructed of brick, stone, and
similar materials, are not electrically connected to the
ground ; therefore the exterior surfaces of the walls con-
stitute local dielectrics to the ground close outside them.
The exercise of the function of local dielectric does not
interfere with the property which all outer walls possess in
virtue of being portions of the uppermost surface of the
earth, viz. the property of forming parts of the terrestrial
collecting plate ; but, as already stated, this condition can
only apply in a passive form to local dielectrics.
If, then, charge should from some cause collect on the
1 I. F 9, 14. 2 VII. C , rj, 0.
3 III. 15, 35, 113, 161, 162, 165.
THE ACTION OF THUNDERBOLTS. 199
VII. B/.
surface of the ground adjacent to the walls of a brick or
stone building, and if a thundercloud should condense this
charge, inasmuch as brick and stone are less restraining
than air, 1 the dielectric afforded by the vertical film of air
immediately in contact with the outer surfaces of the walls,
i.e. afforded practically by the outer surfaces themselves, is
of less restraining power than the adjacent vertical layers of
air not thus in contact with the walls, and hence is apt, in
proportion as the wall surfaces coincide with the line of
least restraint, to hasten explosion ; in other words,
restraint being decreased, and quantity unaffected,
potential becomes increased. 2
The same state of things applies to the surfaces of
wooden and metal buildings insulated from the ground ;
but with these, since wood and metal are less restraining
than brick and stone, 3 capacity is still more diminished.
In fact, the existence of any sort of building not electri-
cally connected to the ground, and consequently forming
a local dielectric, tends, in proportion to the relative
restraining power of the outer surfaces of the walls as
compared to that of air, to cause discharge close outside
the walls ; but experience proves that this tendency, in
the case of buildings of brick, stone, and similar materials,
is not usually per se strong enough to determine explosion,
and is only dangerous to these buildings when they contain
metals on their outer surfaces, or when they present
prominently elevated features.
Metal buildings insulated from the ground, and buildings
of brick, stone, or wood, containing on the exterior surfaces
of their roofs or walls metal not connected to the ground,
are unquestionably sources of danger, inasmuch as the
relative restraint exercised by the metal as compared to
that of air is so much less as to be almost in the category of
attracting explosion. 4
i VI. D a. 2 V. B 1, 7, 12. 3 VI. D a.
* I. E 2, 3, 612. V. B 1, 7, 12. VI. D a.
200 LIGHTNING.
VII. B/
Certain special dangers to which buildings formed wholly
of metal or wood, and acting as local dielectrics, are subject,
are dealt with hereafter. 1
Elevation is a factor that in local dielectrics is of much
influence ; for, the higher the wall, or the more elevated
the features of the building, above the collecting plate
below, the more is the air dielectric supplanted, the more
is capacity (qud restraint) diminished, and the more is
explosion hastened. 2
Especially is the height of metal on a local dielectric a
matter of great moment ; and the explanation of this fact
appears to be as follows : The higher the position
occupied by the metal, the greater is the attraction
exerted over the earth's electricity towards the half-way
point in the air where, through explosion, it meets the
electricity of the clouds, and the more innuentially is the
capacity's restraint lessened. 3
It follows, from what has been advanced, that towers,
spires, domes, belfries, columns, tall chimney-stalks, and
all prominently elevated features of brick and stone build-
ings, are, per se, sources of danger ; and that this danger is
much enhanced by the presence of elevated metal not con-
nected to the ground, e.g. roofs, spindles, finials, weather-
cocks, vanes, crosses, chimney-pots, ornamental ridges, and
eaves gutters. 4
Owing to the great danger occasioned by metal local
dielectrics, it might in some instances be of advantage
to mitigate this danger by connecting the metals to the
ground, thereby converting them into local plates.
The surfaces of glass buildings ought, qua the glass, to
act as greater restrain ers of explosion than air ; and glass
houses would thus contain an element of security. 5 The
wooden or metal framework of the glass might, however,
in many cases, counterbalance its restraining qualities.
1 VII. B i. 2 V. B 1, 7, 12.
3 I. D 49 ; E 6. V. B 1, 7, 12. VI. B b.
* II. E 43. VII. C 3, 16, 17, 18. VIII. C 8. 5 VI. D a.
THE ACTION OP THTODERBOLTS. 201
VII. B g.
A building whose roof or walls were coated with pitch
or tar would, qud this coating, appear to receive additional
security. 1
The sides of shafts leading to mines may probably be
occasionally placed in the same category as the exterior
sides of buildings. 2
It seems quite possible that the ground at the bottom of
a deep colliery shaft may sometimes receive charge ; in
this case the vertical sides of the shaft, especially if they
contained woodwork or metal, would constitute more or
less efficient local dielectrics, and might therefore promote
discharge from the bottom ; and such a discharge would
doubtless ignite any deadly gas that might be present, and
cause one of those dreadful colliery explosions which are
so constantly occurring. 3
The natural features presented by the more or less
vertical surfaces of cliffs, precipices, cuttings, quarries, and
rocky crags, would occasionally constitute local dielectrics.
The ordinary surface of the earth may also form a
local dielectric, as is evidenced by the furrows occasionally
ploughed by explosions. 4
(ff) Accidental Dielectrics formed by Local Plates.
A most important feature of thunderbolt action is the
fact that a local plate may accidentally form a local dielec-
tric to some other plate. 5
A piece of metal forming a local plate on the exterior
surface of a building may form an accidental dielectric to
another piece of metal forming another local plate on the
same building ; or such a piece of metal as either of these
may form an accidental dielectric to an adjacent, though
not immediately contiguous, portion of the earth's surface.
In these two cases the explosion leaps from metal to
1 VI. D a. * ? I. G 34. 3 I. G 42.
4 VII. CIS. 5 VII. B d.
K 3
202 LIGHTNING.
VII. B ,7.
metal, or from ground to metal, and, in the act, probably
causes considerable injury to the building.
These cases of explosions, deviating from what might be
considered the orthodox road, have been termed " lateral
discharges" when they have occurred in connection with
lightning rods, and metallic arrangements (discussed in
Chapter VIII.) have been devised in order to remedy such
erratic courses.
As regards ships, the fact of their hulls forming local
plates would appear not always to cause their masts to
exercise the same function ; for the lower masts of ships
have been rent in a manner that would betoken their con-
dition as dielectrics.
Thus, although the lower mast of a ship is usually elec-
trically connected to the hull, the explosion is liable to
spring from a point on the surface of this hull through the
air to a particular point on the mast much above the level
of the deck, and thus the mast is to all intents and pur-
poses a dielectric.
Hence, a local plate may be so shaped that one of its
higher features acts as a dielectric to the lower portion.
Again, a human body acting as a plate, qua the ground
on which it stands, may yet form a dielectric, by means of
its upper parts, to a patch of charged ground near it, but
insulated from the patch on which it stands.
The general law on this subject would appear to be
that a portion of one local plate may constitute an acci-
dental dielectric to another portion of the same plate,
or to another plate, or to any part of the earth's natural
surface to which the original plate is not electrically con-
nected. 1
All these actions point to the conclusion that an explo-
sion carefully and minutely prepares beforehand its line of
least restraint, according to its own views of what consti-
tutes restraint, 2 and quite independently of any channels
i VII. C 17. VIII. C 7. 3 VII. C 12.
THE ACTION OF THUNDERBOLTS. 203
VII. B h.
of conduction that might on other grounds be supposed to
lead more directly to the electricity in the clouds.
(A) The Protection afforded by the Interiors of Buildings.
The action of thunderbolts in connection with the ex-
teriors of buildings and other hollow constructions having
been considered, the question arises as to how far their
interiors are exposed to danger. 1
Universal experience leaves no doubt that the insides of
houses are, as a rule, safe asylums from thunderbolts, and
it is obvious that this security must be owing to some func-
tion of the roofs and walls.
This function is evidently that due to the fact of the
exterior surfaces of all constructions on the earth's surface
forming parts of the terrestrial plate, whence it follows that
any spaces existing below or within these artificial exterior
surfaces are below or beyond this plate, and consequently
outside of the terrestrial condenser, and hence not subject
to the action of its explosions. 2
Therefore, whether a construction forms a local plate
(as e.g. a ship afloat or a metal building connected to the
ground), or a local dielectric (as e.g. a brick or stone build-
ing), the mere facts of resting on the natural surface of the
globe and of being hollow, constitute to the interior of the
construction a source of protection from thunderbolts. 3
On the same principle, caves and underground construc-
tions would, qua being underneath the terrestrial plate, be
places safe from thunderbolts ; and it is worth noticing
that the ancients were cognisant of this property due to
caves, and took advantage of it. 4
On the same principle also, the ground exactly under-
neath the walls of buildings cannot, as a rule, collect
charge ; and the walls are therefore generally in no danger
of being actually blown up or rent longitudinally,
i I. F 17. 2 V. A ao. II. E 22. * I. F 1 a.
204 LIGHTNING.
VII. B /.
() The Dangers to which Interiors are Halle.
Although, however, we may accept the general rule that
the interiors of buildings, of ships, and of hollow construc-
tions generally, are not exposed to thunderbolt action, still
there are important exceptions to this rule, and the interiors
of constructions forming local dielectrics are frequently sub-
ject to danger. 1
It is evident that the whole substance, the outer surface
of which constitutes a local dielectric, may occasionally
share to some extent with the outer surface the properties
of this dielectric.
Thus, an explosion, instead of confining itself to the ex-
terior surface of a building, may possibly pass within the
substance of its walls or of its roof ; or it may proceed
for some distance over the outside, and then pass inside
through an opening ; or there may be some great attrac-
tion inside which it will pierce the wall in order at
once to reach.
The side or top of a hollow construction may therefore
possess certain features which, independently of exterior
characteristics, as e.g. metals and elevation, might effec-
tively influence explosive action, and might determine a
line of least restraint in the highest degree dangerous to
the inmates of that construction.
We will notice some of what appear to be the principal
conditions that induce explosion not to confine its action
only to the exterior surfaces of constructions, when these
form dielectrics.
In the first place, we must recount what we have already
advanced regarding explosive action generally, viz. that
it always pierces dielectrics, and that it is the film of
air immediately contiguous to the exterior surface of
a wall that it pierces when it apparently passes over this
surface. 2
1 VII. B/. VII. Civ. VII. B c.
THE ACTION OF THUNDERBOLTS. 205
VII. B *.
In the case of a brick or stone building this film is,
as we have said, of less restraining power than air gene-
rally, e.g. than air at only a minute distance from the sur-
face ; but that the brick and stone itself is only slightly
facilitative is proved by the fact that explosion actually
passing through or within it always rends it open. 1
Therefore, and also because the charge causing the ex-
plosion is outside the house, and in most cases the line of
least restraint therefrom to the condensing cloud, whilst
the charge is undergoing condensation, lies also outside the
house, explosion does not usually pierce the brick or stone
walls, nor otherwise enter the house, unless there are in
the walls or interior some special facilities for its progress.
Now these facilities would appear to be of three
natures :
(1.) There might be openings in the masonry (as
there usually are), and during a thunderstorm a
window, door, shutter, or other means of closing
an aperture may be left open, or the aperture may
be permanently open as in some spires, towers,
and belfries, and close to it, inside the building,
there may be a piece of metal, or a human body,
or some other facilitator.
(2.) There may be pieces of metal passing trans-
versely through the walls, as e.g. tie-bars, girders,
cramps, and hoop iron bond.
(3.) There may be pieces of metal in contact with
the inner surfaces of the walls, as e.g. water-
pipes, gas-pipes, clocks, bells.
In all these cases there would be an inducement to some
extent for an explosion to enter a house, though it by no
means follows that the inducement will be sufficient ; and
the last case is the most dangerous of the three, since it
necessitates the piercing of the wall. 2
1 VII. B c. VI. D a.
3 I. E 7, 10. II. G 53. VII. C 3, t, , 8, a, y.
206 LIGHTNING.
VII. B k.
One or more of these conditions would frequently apply
to towers, spires, cupolas, domes, belfries, and other ele-
vated features of buildings.
In every case the danger would probably be enhanced
if the walls were of unusual thinness.
When we come to consider local dielectrics whose walls
or sides are made of metal, wood, or other facilitative
materials, there is evidently a greater possibility that the
thunderbolt may pass to the inside, since these materials
facilitate the passage of the explosion through their sub-
stances ; l and on the whole it is probable that construc-
tions of this nature, e.g. houses, or parts thereof, gas-
holders, and oil tanks, forming local dielectrics, are always
more or less dangerous to their contents, 2 and that wooden
houses, and wooden constructions generally, when in this
category, being less facilitative and more likely to be set
on fire, are more dangerous than metal ones. 3
(K] The Special Danger from Chimneys.
The most frequent source of exception to the security
afforded to buildings by their roofs and walls is the danger
arising from their chimneys, and this is one of the most
fertile sources of injury and death from thunder-
bolts. 4
Dwelling-houses in nearly all civilised countries contain
some means of warming their interiors, or of cooking the
food of their inmates ; and this necessitates some means of
outlet for the smoke and gases due to combustion.
In this country all habitable houses possess, within the
thickness of their walls, one or more nearly vertical chim-
ney shafts or flues.
These shafts extend either from the bottom of the walls
or from various levels up their height (corresponding to
1 VI. Da. 2 VII. B/ ; C1X.
a VII. C 1 /i. 4 II. E 2, 7. VII. C 4.
THE ACTION OF THUNDERBOLTS. 207
VII. B k.
the stories of which the house is composed), to some dis-
tance above the highest points of the roofs, where they
terminate in the prominent, isolated, brick or stone columns
formed by chimney-stacks.
These stacks are frequently themselves surmounted by
tall chimney-pots, consisting of earthenware or metal
cylinders.
At the bottom of each shaft is usually a mass of metal
in the shape of a grate or range, which is generally insu-
lated from the ground by the back hearthstone.
The shafts themselves are necessarily lined with soot or
other unconsumed products of combustion ; and when the
fires are lit, there is a mass of flame at the grate, and a
column of smoke or gaseous matter continually ascending
the shaft and pouring into the air. 1
In the case of a three- storied country house, there is a
kitchen chimney shaft perhaps 80 feet high and 5 or 6 feet
in girth, springing from a large range, which includes
copper, brass, and iron in its composition.
In the case of a labourer's one-storied cottage, the
chimney- shaft is of course much less high ; but probably
it is often in a less cleanly condition than that of the
country house.
Whatever may be the conditions of the building, a
chimney shaft or flue, having its mouth and sides habitu-
ally open to the outer air, may be looked upon as forming
as it were a small quadrangle or court within the enclosure
of the building ; and thus the sides of the shaft may be
considered as exterior surfaces of the building, and as
forming a local dielectric, consisting of a sheet of soot, to
the plate formed by the ground at or near the foot of the
shaft, which ground we must presume is more or less open
through the shaft to the condensing influence of the
clouds.
We have said that the grates are usually insulated from
1 VI. D a.
208 LIGHTNING.
VII. B k.
the ground by the hearthstones ; and as the latter do not
often appear to be recorded as being pierced when a
chimney is the scene of a thunderbolt, probably the poten-
tial of the explosion accumulates on the ground immedi-
ately surrounding the front and back hearthstones, this
accumulation being due to the loss of capacity caused by
the facilitative dielectric formed by the tall column of
soot, 1 aided as it frequently is by the grate, fire, and
smoke.
The explosion, taking in its course any human body
that may be near the line of least restraint, leaps from the
ground near the hearthstones to the grate, and then as-
cends the chimney-shaft through the facilitative soot which
lines it, and emerges at the pot or other summit of the
stack.
The explosion frequently shatters this summit on leaving
it, causing some of the debris to fall down the chimney-
shaft.
The longer the shaft, the larger its girth, and the
sootier its lining, the greater would appear to be the
danger.
In nearly all private houses and cottages which do not
contain much metal on their exterior surfaces, the chimneys
form the probable loci of any explosions that may visit
them, for not only is there danger from the soot-lined flues,
but the stacks or pots crowning them usually constitute the
most elevated features of the buildings.
Particularly at country buildings does injury from
lightning occur at the chimneys ; hence in devising mea-
sures for the defence of life and property from the action
of lightning, the case of these buildings would appear to
demand special attention. 2
The chimney-stalks of furnaces would, from their great
height, independently of their interior linings, be always
apt to form dangerous local dielectrics. 3
1 V. B 1, 7, 12. VII. C 4. 3 II. G 17.
THE ACTION OF THUNDERBOLTS. 209
VII. B I; C.
(I) Simultaneous Strokes of Lightning.
When a building is struck simultaneously in several
places apart from each other, the term " bifurcated," or
" divided," is usually applied to the stroke. 1
From what, however, has been advanced on the subject
of explosions springing from the earth, there will be no
difficulty in conceiving several such explosions occurring
near each other simultaneously, at any place, and particu-
larly at ordinary buildings, which frequently present more
than one easy path for discharge around their walls.
These separate explosions seem especially likely to
happen at buildings where the ground surrounding them
is not in continuous electrical contact, but is broken up
into insulated patches.
These strokes should thus apparently be characterized as
simultaneous or multiple, rather than as divided. 2
(C.) ANALYSIS OF THUNDERBOLT INCIDENTS.
"With reference to the section just concluded, and in
order to permit of a more ready comparison of the theories
advanced therein with the facts related in Chapter III.,
an analysis will now be made of the incidents given in that
chapter, arranged under the following heads, viz. :
(I.) Buildings.
(2.) Ships.
(3.) Metals.
(4.) Chimneys.
(5.) Trees.
(6.) Flagstaff's, masts, &c.
(7.) Telegraphs.
(8.) Human beings.
(9.) Animals.
(11.) Repeated strokes.
(12.) Accurately limited strokes.
(13.) Horizontally directed por-
tions of strokes.
(14.) Acts of mechanical force.
(15.) Local plates.
(16.) Associated local plates.
(17.) Accidental dielectrics.
(18.) Local dielectrics.
(10.) Simultaneous strokes.
1 I. D 33, 34. 2 VII. C 10.
210 LIGHTNING.
VII. C 1 a .
Incidents at which lightning rods were present are
specially considered in Chapter VIII.
(1.) BUILDINGS.
The following are the incidents referring to buildings
(a) Town Churches.
Nos. 36,
78,
107,
142,
51,
84,
118,
144,
52,
89,
132,
145,
53,
91,
133,
155,
59,
97,
134,
188.
62,
(/2) Town Public Buildings.
Nos. 7,
58,
141,
178,
45,
127,
143,
191.
56,
136,
159,
(y) Town Private Buildings.
Nos. 6, 18, 86, j 137, 195,
8, 38, 92, 158, 196,
14, 40, 110, 189, 197.
17, 64, 126, 194,
(8) Country Churches.
Nos. 11,
106,
138,
156,
12,
108,
139,
157, '
13,
111,
140,
166, j
16,
128,
146,
172,
24,
130,
147,
175,
41,
131,
150,
185,
68,
135,
153,
192.
79,
(c) Country Public Buildings.
Nos. 39, 1 73,
114,
180,
46, 91,
121,
181.J
NOB.
THE ACTION OF THUNDERBOLTS.
211
VII. C 1 ,*.
() Country Private Buildings.
9,
35,
103,
177,
19,
37,
105,
183,
21,
49,
115,
184,
32,
55,
119,
186,
33,
66,
120,
200,
34,
67,
160,
201.
(77) Labourer^ Cottage*.
Noa. 167, 182, 203.
($) Powder Magazines.
Nos. 27, I 47, I 84,
28, 82, 87,
(t) Barm, Sheds, and Outhouses.
Nos. 26, 169,
113, 190,
163, 197.
129,
179.
(K) Tents.
Nos. 88, 173.
(X) Miscellaneous Constructions.
Lighthouse . . , . No. 44
Windmill * y -:;v ;- * * v. .42
Monument . * . 74
Chimney Stalk . .../*, 96
Gas-holder 159
Oil Tank 110 1
Nos. 53,
83,
84,
87,
) Buildings set on fire. 2
110, 141,
111, 154,
121, 163,
129,
172,
175,
203.
II. E 34.
I. G 7, 17, 21.
212 LIGHTNING.
VII. 01 v, TT; 2 a.
(v) Injuries inside Buildings. (TT) Masonry rent.
Nos. 3,
51,
158,
Nos. 11,
97,
155,
4,
52,
159,
12,
106,
157,
13,
62,
167,
13,
107,
160,
14,
67,
177,
16,
108,
166,
18,
83,
178,
19,
111,
172,
19,
84,
181,
20,
112,
177,
23,
87,
182,
21,
114,
180,
26,
88,
183,
24,
118,
181,
27,
111,
184,
39,
119,
182,
28,
112,
186,
43,
126,
183,
32,
113,
189,
51,
128,
184,
33,
115,
190,
52,
130,
186,
34,
118,
191,
55,
131,
189,
35,
119,
194,
62,
132,
192,
37,
126,
200,
68,
133,
196.
38,
129,
201,
73,
134,
40,
134,
203.
91,
137,
45,
157,
96,
147,
The cases of buildings struck mentioned in the above
incidents are remarkable chiefly from the lightning rods,
metals, or other important circumstances that are recorded
to have been present at the time. These circumstances
are referred to more fully under their respective heads,
the question of lightning rods generally being dealt with
in Chapter Yin.
As regards the small proportion of incidents in which
buildings of brick and stone are related to have been
struck, but no metals are mentioned, there is very little
doubt, from the nature of these buildings, that they all
contained more or less external metal.
Nos. 5,
63,
70,
(2.) Snips. 1
(a) In motion.
75,
76,
99,
100,
104,
125.
I. G 15, 37.
THE ACTION OF THUNDERBOLTS. 213
VII. C 2/8; 3 a 8.
(ft) In harbour.
Nog. 48,
50,
60,
61,
65,
71,
72,
92,
101,
102,
109.
The more remarkable of the above incidents are those at
which lightning rods were present ; and these are treated
of in Chapter VIII.
(3.) METALS.
(a) External Copper, Bronze, Brass, or Gilding.
Nos. 7,
62,
103,*
131,*
16,
78,*
107,
132,
36,
79,*
111,
133,
51,
81,
117,
142,
52,
96,
128,*
167.*
61,
97,
(ft) External Iron.
Nos. 15,
63,
129,* I
145,
37,
68,
131,*
154,
38,
81,
132,
155,
41,
86,*
135,
178,
42,
106,
136,
180,
47,
112,
138,
183,
51,
114,
139,
188,
52,
115,*
140,
191,
60,
117,
143,
195,
61,
119,
144,
198.
62,
(y) External Lead.
Nos. 47,
51,
52,
58,*
62,
86,*
97,
131,*
132,
133,
180.
(5) Internal Copper, Bronze, Brass, or Gilding.
NOB. 9, I 17, I 88, I 191,
13, 18, 178, 203.
214
VII. C 3 .
LIGHTNING.
(c) Internal Iron.
Nos. 17,
67,
118,*
159,
191,
19,*
83,
157,*
178,
196,
20,
88,
158,*
181,
203.
45,*
In cases marked thus * lightning rods were also present.
We have seventy-three separate cases here recorded in
which metal exerted its attractive or accumulative qualities
to bring about explosion. These cases are well worth
studying, though the details of them are unfortunately, in
some instances, rather scanty.
Those which deserve special attention, either from their
remarkable character or on account of the fulness of the
details afforded, are as follows :
No. 19. Mr. Raven's house and fowling-piece.
20. The soldiers at Martinique.
41. Lausanne Cathedral.
45. Charlestown Prison.
51. St. Martin's Church.
52. Brixton Church.
62. St. Bride's Church.
88. Sutton Camp Mess Tent.
96. Royal William Victualling Yard Chimney Shaft.
106. Black Rock Church.
112. House at Concordia.
117. Paignton Flagstaff.
129. Bruntcliffe Powder Store.
132. St. George's Church, Leicester.
133. Merton College Chapel.
157. Clevedon Church.
158. The banker's house at Lyons.
159. Halifax Buildings.
178. Telegraph School at Malta.
203. Cottages at Ide.
The chimney-shaft case, No. 96, deserves the more notice,
since it is one of the instances that have been put forward
by authorities as showing that lightning is not necessarily
THE ACTION OF THUNDERBOLTS. 215
VII. C 4, 5.
attracted by metal, on the ground that there was none in
the shaft itself, whilst a tower some distance off contained
a great deal and was not struck. The influence of the
large copper roof just below the shaft, where the explosion
is recorded to have ended (but where it probably in reality
began), is not, however, mentioned by these authorities.
In connection with these metallic incidents, two not in-
cluded in the foregoing summaries, viz. Nos. 94 and 95, are
noticeable, as recording how in their cases metal buildings
had for centuries not been struck.
In one case, however, No. 94, the presence of numerous
metal points is mentioned, and there is no doubt that the
other building also contained many angularities and pro-
bably some well-defined points ; whilst both appear to have
had good metallic connection with the ground ; so that the
element of leakage l doubtless, in both instances, overcame
that of accumulation, and the result was that, qua their
metal, these buildings were not found to be sources of
(4.) CHIMNEYS.
Nos. 55,
73,
119,
126.
167,
177,
181,
189,
196,
200,
203.
The following are noticeable :
No. 167. Lossieinouth Cottage.
177. Mr. D. Onslow's house.
203. The cottage at Ide.
Nos.
10, (o)
25,
29, (o)
49
93, (o)
(5.) TREES.
122,
124,
149,
152, (p)
162, 00
164,
165,
173,
174, (c)
187,
193,
198.
N.B. (e) denotes elm ; (o) oak ; (p} poplar ; (c} cherry.
i VII. B d ; F e.
216 LIGHTNING.
VII. 68 a y.
(6.) FLAGSTAFFS, MASTS, KOOFS, AHD WOODEN OBJECTS
GENERALLY (EXCBPT SHIPS 5 HlJLLB).
Nos. 10,
47,
103,
129,
175,
15,
51,
104,
141,
180,
16,
60,
109,
146,
185,
25,
61,
111,
157,
188,
27,
63,
112,
161,
194,
28,
71,
117,
169,
201,
32,
83,
120,
170,
203.
42,
88,
125,
172,
The injuries to flagstaffs would seem to be lessons point-
ing out their dangers to those who are in the habit of
using them as ornamental appendages to their residences, 1
or as architectural features of church towers. 2
(7.) TELEGEAPHS.
Nos. 178, 191.
(8.) PERSONS. 3
These are all fatal cases, except those marked thus *,
which are instances of shocks. Those marked thus J are
cases of fatalities as well as shocks.
(a) Inside houses in towns.*
Nos. 26,
32,
33,
35,
38,
40,
45,*
134.*
(/?) In the open air in towns.
Nos. 23, 148,* 168.J
(y) Inside houses, and under cover, in the country.'*
Nos. 3,
88,*
169,
182,
4,
113,*
173,*
190,
34,
115,t
177,
200,"
35,
167,
181,*
203.
37,*
1 117.
* I. G 13.
2 185.
5 I. G 13.
8 I. G 6, 21.
THE ACTION OF THUNDERBOLTS. 217
VII. C 8, So.
(8) In the open air, in the country. 1
Nos. 1,
90,
129,
164,
10,
98,
H9,t
165,1:
15,
116,
151,
170,
20,
117,*
161,
171,:
25,
122,
1624
193.
82,*
(e) In ships?
No. 72.*
() Under water.
No. 123.*
(77) Riding or driving.
Nos. 15, 161.
(0) Walking.
Nos. 116, 168,J 170.
(t) Engaged in agricultural pursuits.
Nos. 90, 165,: 170, 171,: 1904
(K) On railways.
Nos. 98, 151.
(A.) Sheltering under trees. 3
Nos. 10, 149,: I 165,:
25, 162,: 193.
122, 164,
(/A) In barns, outhouses, or tents.
Nos. 26, 88,* 113,* 169, 173,* 181,* 1904
(v) In labourers' cottages.
Nos. 167, 182, 203.*
(o) In bed.*
Nos. 32, 33, 34, 35, 203.*
1 VII. B t.
I. G 13.
1 I. G 13.
* I. G 13.
218 LIGHTNING.
VII. C 8 7T T, 9, 10.
(TT) In church. 1
Nos. 3, 4, 134.*
(p) Experimenting with lightning rods.
No. 38.
(<r) Soldiers on duty.
Nos. 20, 82.*
(T) Clothes of persons.
Nos. 26, 161, 162, 165.
The following are the cases worthy of the greater atten-
tion, viz. :
No. 15. The Coldstream carter,
38. Professor Eichmann.
115. Mr. Buys,
161. Mr. Woodman.
167. Mrs. Whyte.
168. The persons in Victoria Park.
171. The lads in Beresford's Fields.
195. The platelayer on the Midland Railway.
203. Mr. H. S. Stobart.
From No. 168 we see how an open park in the midst of
an immense city is chosen as the scene of a fatal explosion,
rather than the city itself; and this tends to show that
residents in the country are, generally speaking, more ex-
posed to death by thunderbolts than the denizens of
towns. 2
(9.) ANIMALS.
Nos. 15, 30, 31, 85, 113, 116, 161, 176, 182, 187, 199, 202,
(10.) SIMULTANEOUS STROKES.
Nos. 47,
103,
108,
128,
72,
104,
119,
156,
73,
105,
120,
203.
91,
1 I. G 13. 3 I. G 11, 35, 36.
Nos. 5,
13,
H,
53,
THE ACTION OF THUNDERBOLTS. 219
VII. 1115.
(11.) EEPEATED STROKES.
57,
63,
72,
76,
77,
78,
79,
80,
81,
121,
155,
156.
(12.) ACCURATELY DEFINED STROKES.
Nos. 2,
33,
67,
171,
27,
34,
93,
182.
28,
37,
114,
32,
54,
167,
(13.) HORIZONTALLY DIRECTED PORTIONS OF STROKES.
Nos. 47, I 117, I 157, I 182,
54, 156, 178, 203.
[N.B. The five following groups do not include cases of
lightning rods.]
(14.) ACTS OF MECHANICAL FORCE, EXCLUSIVE OF RENDING
OF MASONRY.
Nos. 2,
33,
103,
156,
5,
51,
109,
166,
11,
52,
112,
173,
12,
54,
117,
174,
15,
60,
119,
180,
16,
61,
120,
181,
24,
62,
124,
182,
25,
63,
125,
183,
26,
67,
128,
185,
27,
71,
138,
187,
28,
75,
139,
195,
29,
86,
146,
196,
32,
88,
152,
X97.
(15.) OBJECTS WHICH, WHEN STRUCK,
PROBABLY
FORMED
LOCAL PLATES.
Nos. 1,
40,
98,
142,
162,
176,
3,
50,
110,
143,
164,
190,
4,
63,
116,
144,
165,
193;
10,
76,
122,
145,
168,
198,
23,
82,
135,
149,
169,
199,
30,
85,
136,
151,
170,
202.
31,
90,
140,
154,
171,
L 2
220 LIGHTNING.
VII. C 1618 ; D.
(16.) OBJECTS WHICH, WHEN STRUCK, PROBABLY FORMED
LOCAL PLATES ASSOCIATED WITH LOCAL DIELECTRICS.
Kos. 20,
39,
51,
52,
96,
97,
114,
117,
120,
132,
134,
138,
139,
147,
158,
178,
191.
(17.) OBJECTS WHICH, WHEN STRUCK, PROBABLY FORMED
LOCAL PLATES, ACCIDENTALLY CONSTITUTING LOCAL
DIELECTRICS.
Not. 15,
25,
26,
29,
48,
56,
60,
61,
63,
71,
75,
93,
104,
109,
113,
124,
125,
127,
129,
152,
159,
161,
173,
174,
187.
(18.) OBJECTS WHICH, WHEN STRUCK, PROBABLY FORMED
LOCAL DIELECTRICS.
Nos. 2,
27,
54,
107,
141,
177,
194,
7,
28,
67,
111,
146,
180,
195,
9,
32,
68,
112,
155,
181,
196,
11,
33,
73,
115,
156,
182,
197,
12,
34,
74,
118,
157,
183,
200,
13,
35,
81,
119,
160,
184,
201,;
14,
36,
83,
121,
163,
185,
203.
16,
38,
84,
126,
166,
186,
17,
41,
87,
130,
167,
188,
18,
42,
105,
133,
172,
189,
24,
53,
106,
137,
175,
192,
(D.) ATMOSPHERIC DIELECTRICAL CONDITIONS.
We propose now to treat of the principal special con-
ditions of the air dielectric that would appear to affect
explosion, 1 so far as these conditions may be said to be
independent of the question of electrical leakage.
This question, which would be of great importance in the
consideration of the state of the air previous to the develop-
ment of thunderstorm elements, is dealt with in Section F
of this chapter.
1 III. 14, 15, 50, 85, 94, 117, 157, 178, 183.
THE ACTION OF THUNDERBOLTS. 221
VII. D a.
(a) The Influence of Rainfall.
A condition almost always present with thunderbolt
explosions is rainfall, and its action deserves, therefore,
special attention.
The remarks applied hereafter to rain would also apply,
mutatis mutandis, to the occasional substitutes for rain, viz.
snow and hail.
The under-surfaces of the clouds, whence rain springs,
being rendered more moist by its eruption than they were
before, must become more collective, and, therefore, on the
principle submitted in Section A, must exert in a given
time a proportionally greater condensing power on the
potential of the earth's collecting plate. 1
The air dielectric being impregnated with the rain drops
becomes more facilitative of explosion, i.e. exercises less
restraint on the recombination of the electricities accumu-
lated on the two plates ; or, to express it differently,
capacity being reduced and quantity unaffected, potential
is increased. 2
Lastly, the earth's surface becomes more collective owing
to the access of moisture it receives, and therefore its
potential, like that of the clouds, is increased. 3
Thus we see that in three distinct ways rainfall tends to
increase potential and to bring about explosion, and,
taking all the circumstances into consideration, we may
probably conclude that, as a rule, rainfall is the immediate
practical cause of the occurrence of thunderbolts.
In accordance with this idea the following three con-
ditions would probably be those which would generally
precede these explosions, viz. : First, a collective portion of
the earth's surface already charged from below with a
certain quantity of electricity. Secondly, a low dense rain
cloud approaching the zenith of the charged place, and
1 VI. D a. VII. A a. V. B 1, 7, 12.
3 VI. D a. VII. A a.
222 LIGHTNING.
VII. D I.
ready on arrival within inductive range of it, to increase
its potential by condensation. Thirdly, a fall of rain sud-
denly reducing the capacity of the air whilst the accumula-
tion of potential on the cloud and the place is proceeding ;
this rainfall being, in fact, the last straw that breaks the
camel's back. 1
The density of the rainfall would doubtless have an effect
on the restraint of the air ; 2 and a thunderstorm having
once commenced, it seems reasonable to expect that the
heavier the rainfall that should accompany it, the more
numerous, cceteris parilus, would be the thunderbolt explo-
sions that would occur during its continuance.
(J) The Temperature of the Air.
The restraining power of the air is probably influenced in
some degree by its temperature ; but on this, as on the
question of the influence of the density of rainfall, there
appears to be but little knowledge extant.
Thunderbolts occur more numerously in this country
during the warm than during the cold season ; but they
are by no means absent during the latter. 3
They occur frequently in all countries and regions at
night-time ; 4 though in this country their appearance is
generally by day.
The reason for the formation of snow and hail is of
course associated with atmospheric temperature ; and when
hail accompanies thunderstorms, they are said to be usually
of a severe character ; 5 but the connection between hail
and thunder storms has not been well accounted for.
In England we probably suffer far less from hail than is
the case in France, where, in the vine regions, it appears
1 I. D 18. II. G 29. 2 VI. D a.
3 III. 12, 24, 44, 4648, 5961, 72, 76, 106, 117, 127, 136, 144,
147, 182.
* III. 3235, 53, 106, 112, 125, 181. 5 III. 117. I. C 23.
THE ACTION OF THUNDERBOLTS. 223
VII. DC; E0.
to constitute a dreadful scourge, and to be generally accom-
panied with much thunder and lightning. 1
It was thought by Arago that the same means that would
tend to prevent thunderbolts might also tend to prevent
hail ; 2 and it certainly appears possible that increased
researches as to the action of lightning may also throw
light on that of hail.
(c) Atmospheric Electricity.
The presence of charge in any portion of the dielectric,
independently of that on the plates, would probably tend to
affect its restraining power. 3
It appears from experiments that have been made that
the stratum of air lying nearest the earth is generally more
or less negatively electrified. 4
Thus the lower regions of the atmosphere may possibly,
from this cause, possess in some places degrees of restraint
different from what they do in others.
It can be conceived that the presence of this atmospheric
electricity in any large amount on or over any particular
portion of the terrestrial plate might materially facilitate
explosion thereat, but our knowledge of atmospheric elec-
tricity appears to be so slight that it is impossible to come
to any conclusions on the subject. 5
(E.) CLOUDS AND CLOUD EXPLOSIONS.
We will now notice the principal conditions, tending to
charge and discharge, connected with the clouds ; and here
we enter into a consideration of the discharges that occur
between clouds and clouds, viz. cloud explosions.
(a) The Electrical Conditions of the Clouds.
The charging to some extent of the surface of the
ground from the action of electricity below it (due to causes
i I. C 21. z I. C 22. 3 I. 1014.
* I. C 8, 9. I. C 2, 3.
224 LIGHTNING.
VILE I.
of which, we are as yet ignorant) being the first step
towards the formation of a thunderstorm condenser, the
second step is probably the piling up of clouds, at no great
elevation, over a particular area. 1
The causes of the collection of clouds in masses suitable
to the development of these condensers are probably of a
purely meteorological nature.
A condenser having been formed, the condensive power
of the condensing plate formed by the under-surf aces of the
clouds would be an element affecting explosion. 2
This condensive or collective power would probably be
influenced by the amount of moisture 3 present, and by the
cloud's area and shape.
The effect of rainfall in increasing the moisture of the
under-surfaces of the clouds has already been suggested ;
and, evidently, the greater the area of this surface and the
more parallel it lies to the earth's surface, the greater is
the chance of any charge already collected on the latter
being condensed by the cloud during its passage over it.
(J) The Electricity due to the Conversion of the Clouds into
Rain.
It seems probable that the potential of the under-surfaces
of the clouds is affected, independently of their induction
by the earth, by a disengagement of electricity due to the
sudden conversion of the lower portions of these dense
masses of vapour into rain. 4
The electricity thus formed would doubtless go to swell
the induced charge already existing ; for if it were of an
opposite nature the two electricities would tend to neutralise
each other, and thus rainfall would tend to prevent thunder-
storms, which is a very unlikely state of things.
1 I. C 2730, 36 ; D 27. 2 VII. A a.
a VI. Da. * I. C 16, 17, 118.
THE ACTION OF THUNDERBOLTS. 225
VII. E C.
(c] Cloud Explosions.
A cloud explosion is the explosion of a condenser formed
by two separate clouds, one of which, constituting the
collecting plate, has received its charge by induction from
the earth. 1
The degree in which the clouds are broken up into
detached masses must be a matter of great moment ; for,
if they constitute a single huge plate, there is no possi-
bility of explosion taking place from it except with the
earth.
But if there are a number of separate insulated clouds,
a great chance then exists of these clouds becoming dis-
charged by explosions with each other instead of with the
earth, or, in other words, of cloud explosions occurring in
lieu of thunderbolts. 2
The main factor in the problem whether, in the case of
a number of detached clouds, explosions would occur
between them or with the earth, would be their relative
distances at any moment from each other and from the
earth.
The mobility of these light masses of vapour renders it
likely that they would frequently sail within explosive
range of each other before the necessary conditions for
their explosion with the earth had ripened.
The directions, then, in which they might move would be
very material circumstances, and the great causes influen-
cing these directions would appear to be three in number,
viz. :
(1.) Wind, or air currents.
(2.) Electric attraction and repulsion. 3
(3.) Gravity. 4
Our knowledge of the nature of air currents would lead
to the belief that their force would generally act rather in
1 I. D 10, 16. VI. E a. 2 I. C 33. VI. A a.
3 I. C 31, 32. V. A 7, 8. * I. C 31, 32.
L 3
226 LIGHTNING.
VII. E d.
a lateral than in a downward direction, and therefore would
tend to promote cloud explosions rather than thunderbolts.
Electric attraction would, qua the earth's influence, be a
downward force ; whilst both attraction and repulsion from
the adjacent clouds would act more or less laterally.
Thus when the clouds were consolidated in one great
plate, the earth's attraction would be a considerable
element in hastening thunderbolt explosions ; but when
there were several clouds floating about, it would be
difficult to conjecture what the net result of all the electric
attractions and repulsions would be in hastening or delay-
ing such explosions.
Gravity of course acts in a direction tending to cause
thunderbolt explosions.
It would appear, then, that during a thunderstorm the
circumstances of the clouds are considerable elements in
determining whether the explosions that mark its progress
will take the form of cloud explosions or of thunderbolts,
(d) Thunderstorms.
The subject of the motion of the clouds leads to a con-
sideration of the motion and cause of thunderstorms. 1
Thunderstorms, having commenced, generally move in
a certain direction, over a certain area or region, before
they disappear. 2
The explanation of the commencement and progress of
a thunderstorm is probably as follows : The clouds which
cause the storm move, more or less together, in a particular
direction (mainly that of the wind), and this direction
happens to be over ground that is previously charged from
below.
The storm thus becomes a thunderstorm ; and the clouds
during their progress are repeatedly electrified by induction
by the fresh places, most favourably adapted for this
1 I. G 38. * I. C 43, 44.
THE ACTION OF THUNDERBOLTS.
VII. F a.
action, whose zeniths they are constantly approaching;
and each electrification results sooner or later in a cloud
explosion or a thunderbolt.
As soon as these clouds arrive over uncharged ground,
or mount higher in the atmosphere, or disperse (the rain
ceasing in both these latter cases), the thunderstorm of
which they are the immediate cause, ceases, and the atmo-
sphere resumes its normal state.
There is apparently no reason for assuming that the
surface of the earth is not frequently charged from below
at times when no thunderstorms happen, and when the
weather is perfectly fine ; : and these storms are probably
due to the fortuitous conjunction of low piled-up masses of
rain cloud and charged surfaces of ground.
(F.) TERRESTRIAL EETTJRN STROKES.
(a) Nature of Terrestrial Return Strokes.
Terrestrial return strokes, or induced discharges of terres-
trial electricity, affect the surface of the earth generally, and
human beings, animals, and telegraphs in particular. 2
The conditions necessary to induce return strokes are of
two kinds, viz. :
1st. The charge on any portion of the earth's sur-
face, or collecting plate, being condensed by a
cloud, and an explosion occurring between this
cloud and another one ; in other words, whenever
a cloud explosion occurs.
2nd. The charges on two or more portions of the
earth's surface, or collecting plate, adjacent to,
but insulated from, each other, becoming con-
densed to different degrees of potential by the
same cloud, and an explosion happening between
1 I. C 3.
* I. D 5158, 6163, 6571, 76. V. B e. VI. E a.
228 LIGHTNING.
VII. F I.
this cloud and that portion of ground whose
charge was at the highest potential ; and this
would, in fact, generally be whenever a thunder-
bolt occurred.
The portion of the earth's surface in the first case, and
the unexploded portions in the second, must then necessarily
lose so much of their potential, and therefore (capacity being
unaltered) of their charge, as was due to the condensing
action of the cloud before, in each case, it exploded.
These charges thus lost return to meet and recombine
with the oppositely electrified particles which they had
temporarily displaced and driven into the earth when they
were drawn to and collected on the surface by the cloud's
condensing action ; and thus terrestrial return strokes are
occasioned.
(J) Return Strokes induced by Cloud Explosions.
Return strokes of the first order, viz. those induced
by cloud explosions, must necessarily be beneficial to the
earth's surface and to its inhabitants ; for the oppressive
feeling that occurs shortly previous to, and during the pre-
valence of, thunderstorms a feeling due to the accumula-
tion of potential brought about by the condensing action
of the clouds is removed, the air is (to use the popular
expression) "cleared," and the slow chemical decomposi-
tion which manifests itself during this period in certain
substances, such as milk and beer, a process likewise due
to the abnormal amount of potential present, ceases. 1
Whenever, then, cloud explosions happen, i.e. when
lightning appears in the heavens only, and not at the
earth, corresponding return strokes take place on the
earth's surface, such strokes being chiefly manifested by
their general malaise-removing results.
1 I. C 19, 37, 38.
THE ACTION OF THUNDERBOLTS. 229
VII. F C.
(c) Return Strokes induced by Thunderbolts.
Return strokes of the second order, though induced by
thunderbolts, are never likely to be so dangerous as these
explosions ; for there is no scope in the nature of return
strokes for violent manifestations, since they can only
occur within a collector (the presence of a non-collector
being, as we have seen, essential to explosive action), and,
in leaving that collector, they return through it, instead of
going out of it into a non-collector, as a thunderbolt does.
The effect of a thunderbolt-induced return stroke on a
human being is usually a shock to the system, 1 the
effects being generally temporary, and lasting not more
than a few hours ; and there appears to be little, if any,
ground for deeming that this shock is ever of a fatal
nature ; for when a person is struck dead by lightning, it
must be generally quite out of the power of any bystanders,
or witnesses (who cannot possibly have been expecting the
stroke), to give an opinion as to how the event occurred ;
and any such evidence as to the fact of fatal return strokes
can hardly be conclusive.
As regards the Coldstream incident, 2 which has been
attributed to a return stroke, 3 the fact of thunder accom-
panying it would alone appear sufficient to render such an
idea nugatory ; whilst the circumstance that two persons
who happened not to be far off at the time stated that
they had seen no lightning, does not preclude the strong
probability that there was lightning of some kind, and
during some portion of the thunderbolt's passage through
the air, especially when we remember that lightning
necessarily requires a certain condition of atmosphere for
its manifestation, and that it is possible that in certain
weathers this state is not always present in every stratum
of air through which an explosion may have to pass ; thus
the phenomena of " fireballs" are probably manifestations
1 VII. C 8. * III. 15. s VI. B a.
230 LIGHTNING.
VII. F d.
of thunderbolt lightning under abnormal atmospheric con-
ditions. 1
Return strokes are generally experienced, as might be
expected, by persons in the immediate vicinity of the scene
of a thunderbolt explosion ; and in these cases it is often
remarkable how the thunderbolt selects one person as its
victim, whilst others, who may be close to this person at
the time, are either totally unaffected or merely receive
shocks.
This shows within how minute an area a thunderbolt
occurs, how exactly it chooses its place and path, and how
circumstances that are generally regarded as trivial (for no
attempt seems ever to be made in this country to investi-
gate the reasons for such selections) doubtless make all the
difference whether a person is killed or not. 2
(d) The Effect of Return Strokes on Telegraphs.
When telegraph wires form part of the collecting plate
whose condensed electricity departs in a return stroke,
whether such be induced by a cloud explosion or by a
thunderbolt, these wires are apt to be traversed by
currents of more or less strength, which are liable to injure
the instruments at the stations. 3
Apparatus called " lightning protectors " have, however,
been devised, which prevent much practical inconvenience
to telegraphy from the effect of these abnormal currents, 4
though they are less to be depended on for protecting the
instruments from thunderbolts. 5
When the cables of submarine mines, or the wires of
land mines and blasts, become the loci of return strokes,
the induced currents set up are clearly sources of the
utmost danger, and need to be guarded against with the
greatest vigilance. 6
1 I. D 4, 25, 26. III. 50, 85, 178, 183. VII. C 12.
3 I. D 6670. * I. D 74, 75, 77. 5 VII. C 7.
6 I. D 71, 76.
THE ACTION OF THUNDERBOLTS. 231
VII. G a.
The question of the interference of thunderstorm elec-
tricity with artificial electrical arrangements is obviously
one that forms part of the practical science of these
arrangements ; thus any detailed consideration of it hardly
comes within the limits of this treatise.
(Gr.) TERRESTRIAL LEAKS.
We have already submitted that electric leaks are of two
kinds, the one due to the porosity of all insulators, and
the other to the existence of angularities on the surface of
collectors. 1
Leakage of either kind from particular places on the
earth's surface, 2 through the air, prior to the formation
of the cloud condensing plate, would evidently materially
affect the collection of electricity at such places, and would
probably sometimes determine whether a storm passing
over them became a thunderstorm or not.
Terrestrial leakage is thus an element of great import-
ance, and its presence must tend considerably to lessen the
chances of explosion.
We will first treat of the principal sources of porosity in
the atmospheric insulator, and then of the angularities
that occur on the terrestrial collector.
(a) Atmospheric Porous Leah.
Smoke and foreign gases in the layer of atmosphere
immediately overlying the earth appear to have the pro-
perty of more or less piercing this layer.
Hence, large cities where coal is burnt, the smoke of
which usually forms a canopy over them, are probably
by this circumstance defended to some extent from
thunderbolts.
The density of the atmosphere would seem to be another
agent affecting leakage, since the pores of the air may be
considered open in inverse proportion to its pressure.
i V. B 1517. ' VI. D a.
232 LIGHTNING.
VII. G b.
The state of moisture of the atmosphere has probably
considerable influence on leakage; and a saturated con-
dition of the air would doubtless tend to increase its
porosity.
Aurora, and heat (or summer) lightning would appear
to be luminous manifestations of porous leaks in the
atmosphere; the one, between the earth and the upper
atmospheric strata, 1 and the other, between two of these
strata. 2
Waterspouts appear to be mechanical manifestations of
atmospheric leaks; for under circumstances which show
that electricity is present, we see clouds depressed, and the
movable surface of the earth, i.e. waters, elevated to
meet them. 3
(b) Terrestrial Angular Leaks.
When we come to those sources of leakage which are
derived from conditions appertaining to the earth's surface,
we are on much surer ground than we can ever be in the
case of the atmosphere.
There is no doubt as to the fact that projecting angu-
larities on the surfaces of collectors lose their capability of
holding charge in proportion to the collectivity of their
material and to the acuteness of their projections ; whence
it follows that a sharp metallic point on a collector con-
stitutes a great leak, and the discharge it occasions is of
the nature of a continuous escape of electricity from the
collector, through a rift in the enveloping insulator, to
meet the induced electricity which necessarily flows towards
it from the nearest separate collector. 4
Practically, the only angularities that materially exercise
this function are those made of metal, other substances not
having sufficient accumulative power, i.e. the particles of
electricity gathered on them are not able to exert a suffi-
1 I. C78. VI. A a, ;E. 2 I. D 4, 20. VI. AayEa.
3 I. C t. * V. B 18.
THE ACTION OF THUNDERBOLTS. 233
VII. G e.
ciently powerful repulsive or dispersive action on each
other. 1
Now, as the earth's surface does not present naturally
any metallic angularities, although such projections as are
offered by blades of grass, foliage, thorns, branches of
trees, and shrubs, and even sharp-pointed rocks, do doubt-
less act in some slight degree as leaks, we are, in order
to obtain dispersers of practical value, compelled to use
artificial means.
By the employment, then, of such artificial means as
metal points, we have the power of tapping the electricity
of the earth, and of assisting to rid its surface of the charge
that may collect thereon from below.
(c) The Value of Metal Points in Relation to the Earth.
If we assent to the theory that the clouds form the
collecting plate, and that the earth's surface receives its
electricity therefrom by induction, 2 we must relinquish
the idea of dispersing the terrestrial electricity until the
thunderclouds have actually arrived and the process of
condensation has commenced.
Now, although, at that time, metal points on the earth's
surface would undoubtedly have a considerable duty to
fulfil in ejecting the earth's charge as quickly as they
could, and in helping to dissipate that of the thunder-
clouds, yet this duty would be far less valuable than that
which these points would carry out if the earth's surface
should form the collecting plate; for in that case they
would cause leaks from the original charge, and would
reduce its quantity and potential before the thunderclouds
arrived and the condenser became formed.
In the case first supposed there is reason to believe that,
after the clouds had begun their condensing operation,
potential would be liable to accumulate with such rapidity
1 II. C 39. 2 VI. A a.
234 LIGHTNING.
VII. G e.
that, however effective the points might really be, they
would not be able to throw off the charge at an equal rate,
and thus explosion would not in most cases be pre-
vented ; l but if the earth form the originating plate, and
if the ground have been thoroughly tapped beforehand,
there would be little or no charge left on it to be condensed
when the clouds arrive, and consequently explosion would
be much less likely to occur. 2
It is thus evident that when the earth is treated from the
point of view upheld in this treatise, viz. as the collecting
plate of the terrestrial condenser, and the originator of
thunderstorm electricity, 3 the value of metal points in
tending to prevent thunderbolts becomes greatly en-
hanced.
We look on the earth, then, under this aspect, as a
receptacle of force in a more or less pent-up state, and,
like all such receptacles, as needing valves or outlets for
the escape of such force before it becomes explosive. 4
The medium by which, in the case of the earth, this
explosive stage is liable to be reached, is the thunder-
cloud; but this, fortunately, only comparatively seldom
exists ; and, between its intervals of existence, it is
necessary to tap the earth's surface, or those portions of it
which we are particularly interested in protecting, in order
that when this cloud does appear it may have little or
nothing to work upon ; and thus the terrible result of its
work, the thunderbolt, may be averted.
The luminous phenomena known as St. Elmo's Fires,
which, in thunderstorm weather, appear at the upper
extremities of pointed metals connected with the earth, are
tangible proofs of the tapping powers of metal points ; 5
so also are the brush discharges artificially produced from
points on charged metallic collectors ; 6 and the flashes
that were drawn by the pioneers of lightning engineering
1 II. C 45. 2 II. C 11, 30, 51, 5355 ; G 40. 3 VI. A b.
* II. E 27. 5 I. C h. 6 II. C 11, 31, 52, 53.
THE ACTION OF THUNDERBOLTS. 235
VII. G d.
with their pointed rods give testimony to the same
effect. 1
(d) Terrestrial Valves afforded by Features of Civilisation.
We propose to notice now some of the principal valves
to terrestrial electricity afforded by various features of
civilisation, apart from any apparatus specially devised to
defend life and property from the action of lightning ; and
our attention will first be directed to the case of large
towns.
We have already alluded to some probable reasons for
the apparent comparative immunity possessed by large
towns in regard to thunderbolt injuries, viz. the absence of
open fields and vegetation, the pavements immediately
surrounding the houses, and the smoky atmospheres. 2
Another reason, however, and probably a still more
efficient one, lies in the fact that the surface crust of the
ground in all large towns is permeated by much metal in
the shape of water-pipes and gas-pipes, and these pipes
have all of them terminations, more or less angular, above
ground, e.g. water-cocks and gas-burners within the
houses, and the burners of gas standards in the streets.
We thus obtain two "efficient systems of electrical taps,
exposing comparatively little metallic surface to the action
of the clouds, and preventing any charge that may rise to
the earth's surface from accumulating at any particular
place, by quickly dispersing such charge through the
numerous angular exits afforded ; for the ejective power
inherent in such of these exits as occur inside buildings
is not affected thereby. 3
Towns furnished with water or gas supply would, there-
fore, seem to be well tapped, and to be fairly protected, both
as regards their houses and the open streets, from injury by
thunderbolts.
In the case of the country, the network of metal formed
i II. C 13, 14, 22, 23. 2 VII. A c, e ; G a. 3 V. B 20.
236 LIGHTNING.
VII. G e.
by the railway system probably constitutes an efficient
source of leakage. 1
The metals are practically connected with the earth's
surface, and they afford, together with the engines running
on them, numerous angularities through which the terres-
trial electricity may escape.
The telegraph posts, which are now erected along the
main roads, must also, by means of their earth wires, con-
stitute good taps. 2
It thus appears that four distinct features of civilisation,
otherwise beneficial, viz. water supply, gas supply, rail-
ways, and telegraphs, tend also to protect life and
property from thunderbolts.
(e) The Angular Leakage of Metals.
Allusion has already been made to the conditions of
leakage inherent in all metal local plates. 3
This is due to the impossibility of manufacturing metal
articles without angularities, more or less sharp, in the
shape of corners and edges.
Under this aspect, the metal objects that would furnish
sources of leakage in a minimum degree would be flat
roofs, 4 domes, balls, and curved surfaces.
Ordinary houses are probably occasionally protected to
some extent by the fact of their rain-water pipes entering
the ground at one or more places close to the outsides of
their walls, these pipes either terminating above in hopper
heads, or being connected to the eaves gutters, both of
which furnish ridges and angularities. 5
It has to be borne in mind that it is only when metals
are metallically connected to the ground, and so form local
plates, that points and angularities can be of any advan-
tage to them ; for there is no reason to suppose that, when
1 VII. A/. * II. B 28. 3 VII. B d.
* III. 51, 52, 86, 96, 97, 115, 131133. II. B 54.
5 II. E 3, 8, 33.
THE ACTION OF THUNDERBOLTS. 237
VII. G e.
they form local dielectrics, any particular shape they may
have is of the slightest consequence.
, It will be evident, from what we have advanced, that
all metals in local plates present two antagonistic
elements, the one tending to accumulate charge, and the
other to disperse it ; and in the difficulty, and probably
the impossibility, of deciding whether the dispersive
qualities of a metal surface act at the same rate as its
accumulative powers, lies the great danger of using metal
at all on the outside of buildings, however well such metal
may be connected to the earth. 1
i I. E 112. II. G 3, 4, 8, 14, 15, 2527.
YIIL A a.
CHAPTEE VIII. THE PEESENT SYSTEM OF
LIGHTNING EODS.
(A.) OBSERVATIONS ON THE HISTORY OF LIGHTNING EODS.
(a) The Invention of Lightning Rods.
WE have now arrived at the stage for considering the
means generally adopted for defending constructions, e.g.
buildings, ships, and monuments, from the action of thun-
derbolts.
It has been shown how, through the ejective power of
metallic points, we possess to some extent a grasp over the
action of terrestrial electricity.
This power was discovered by Benjamin Franklin ; and
it enabled that great man to devise for the protection of
buildings and other constructions the arrangement of
pointed metal known as the lightning rod. 1
A lightning rod, as invented by Franklin, and as now in
general use, 2 may be said to consist of three parts, viz. :
(1.) A root, earth connection, or underground por-
tion, which is usually adjacent to the base of the
most elevated feature of the building.
(2.) A stalk, i.e. a rod, band, tube, or wire rope,
proceeding from the root more or less vertically
up the outside of the building, and projecting
some distance above its uppermost feature.
( 3. ) A point forming the upper extremity of this stalk.
The fact that since Franklin's time no material alteration
in the design or the construction of the lightning rod has
1 II. A 1216 ; C 14, 42. 2 IV. 148.
THE PRESENT SYSTEM OF LIGHTNING RODS. 239
YIII. A b.
been adopted, is a remarkable testimony to his genius ;
and the circumstance is all the more notable when we
remember that the science of electricity was then in its
infancy, and had not as yet been applied to practical pur-
poses.
The lightning rod was probably the earliest application
of electricity to a useful object.
The scope of lightning rods, however, although of a
most beneficial nature, has never been connected with
economical or commercial necessities, and therefore the art
of lightning engineering has perhaps not received that full
and searching consideration to which more business-like
arts are generally subject.
The development of the electric telegraph, and of all the
valuable employments of current electricity that followed
in the wake of Yolta's grand discovery, has naturally so
absorbed the energies and researches of eminent physicists
that a contrivance not intended to meet the wants of every-
day life, but merely to provide an insurance (and, in the
opinion of many, a very uncertain one) against a some-
what unlikely accident, has necessarily been somewhat
eclipsed by more cogent interests.
It is submitted, however, that our present knowledge of
the laws of electricity and of the terrestrial constitution,
taken in conjunction with the mass of experience that
has been furnished by the accidents occasioned by thunder-
bolts during the one hundred and thirty years that have
elapsed since the introduction of lightning rods and espe-
cially with that portion of this experience that bears on
the influence of these rods enables us now to rear a
superstructure on Franklin's foundation, and to deal far
more thoroughly with the subject than he possibly could
have done.
(b) Theory of the Functions of Hods.
There seems but little doubt that Franklin's fundamental
object was to elicit the charge from the ground by means
240 LIGHTNING.
VIII. A I.
of the lightning rod's point, 1 and that the idea of offering
the lightning an easy conduct to the ground by means of
the stalk, was the result of a later conception of the theory
of the rod's action, a conception that probably received an
impetus from the greater knowledge of electrical currents
that accrued from the labours of Volta and his successors.
At the present time the lightning rod is generally held
by physicists to possess two functions ; one, by means of
the root and point, tending to prevent thunderbolts ; and
the other, through the medium of the stalk, tending to
facilitate their passage after they had occurred, so that
they should effect only a minimum of injury. 2
The latter function is that which has been most readily
adopted, especially in England, where probably a propor-
tion of quite nineteen persons out of twenty are ignorant
'of any other.
The general supposition in this country appears to be that
Franklin with his kite drew lightning from the skies, 3
and by thus producing it (as it were) in a tame and con-
trollable form, was enabled to identify it with the electric
spark ; and that then, by analogy of reasoning, he con-
ceived the idea of fixing metal rods to buildings in order
that, if the lightning struck them, it might be drawn down
the rods as it had been drawn down the wet cord of his
kite. 4
What really happened, however, in the case of Franklin's
kite was this: During the progress of a thunderstorm, the
point that surmounted the kite elicited electricity from the
ground in the visible form of an electric spark leaping
across an air gap of slight length purposely left in the
connection of the kite apparatus with the earth. 5
This apparatus was simply a species of lightning rod,
and the great elevation given to its point by the kite
1 II. A 15; C 14,42.
2 II. C 4245 ; G 31, 44, 48. VI. B a.
3 II. A 20 ; C 42. VI. B a.
* II. A 14. 5 II. A 14.
THE PRESENT SYSTEM OF LIGHTNING RODS. 241
VIII. A b.
arrangement was quite unnecessary, as was proved by
D'Alibard, who, at Franklin's instigation, produced the
same results by means of a pointed iron rod of no great
height. 1
It has already been explained that an electric spark
across a gap in a conductor is an explosion of a condenser
temporarily formed by the gap and the ends of the con-
ductor at the sides of the gap ; 2 and, in accordance with
this view, the reason for the sparks and flashes, drawn by
Franklin, D'Alibard, De Eomas, and others, is as fol-
lows :
The charge on the surface of the ground was condensed
by the thundercloud to a high state of potential ; conse-
quently, the lower part of the apparatus electrically con-
nected to the ground shared this state.
Charge of an opposite nature was then induced, across
the air gap, on the lower end of the disconnected upper
part of the apparatus, the complementary electricity being
driven upwards to the point, and then (assisted by induction
from the cloud) ejected thereat.
Almost as fast as explosions in the shape of sparks
occurred across the air gap, fresh charge accrued from the
ground, and fresh electricity of the same nature was driven
out at the point ; and thus, through the leaking action of
the point, 3 which allowed room for the induced charge
above the gap to accumulate to explosive potential, a suc-
cession of sparks was produced during the period that the
thundercloud remained within condensing range. 4
Eripuit fulmen ccelo is therefore merely a figure of
speech ; 5 for what Franklin saw was not lightning ; nor
has any one ever intentionally drawn lightning from
heaven, or created thunderbolts. Franklin's experiment
only tended to confirm the preconceived idea that lightning
was associated with electricity, and was probably a huge
electric spark ; 6 and it proved that pointed metal rods had
1 II. A 13. 2 VI. B b. a II. C 5355.
* II. A 13, H, 22, 23. * II. A 20. II. A 6, 7, 9, 12.
M
242 LIGHTNING.
VIII. A c.
the power of ejecting electricity from the ground, at all
events whilst thunderstorms were in progress, and the
result was the conception of defending buildings by means
of these rods.
There is hardly any doubt that the supposition of light-
ning passing down lightning rods into the ground arose
from the prevalent view that its direction was invariably
from the clouds to the earth. 1
That Franklin himself gradually fell in with this theory
of the function of lightning rods is almost certain ; and the
probability is that, after he had established the practice of
his invention, he had neither inclination nor time to attempt
to elaborate its theory.
It is not, then, to be wondered at that, in England, the
term " lightning conductor" soon superseded that of light-
ning rod, and that the function of the rod's point was,
for a long time, almost ignored ; 2 although, inasmuch as
the existence of lightning depends on the absence of
conducting bodies, the expression " lightning conductor "
clearly constitutes a contradiction in terms.
On the Continent, the question of lightning rods in
general, and of the preventive power of their points in
particular, appears always to have received more attention
than in this country : 3 it was from France that the
knowledge of Franklin's invention spread into England; *
and it is worthy of notice that the term paratonnerre, used
by the French to indicate a lightning rod, much more
clearly denotes its preventive action than the corresponding
English term.
(c) The Opposition to the Use of Rods.
It would appear that when lightning rods were first made
known, and for some three-quarters of a century after-
1 VI. B a. 2 II. C 12, 35 ; D 33, 38.
3 I. G38; II. G34. * II. A 12.
THE PRESENT SYSTEM OF LIGHTNING RODS. 243
VIII. A C.
wards, much opposition to their use was manifested, and
even among men of known scientific attainments. 1
Attempts have been made to show that this opposition
was based on ignorance ; but it is unquestionable that these
opponents of rods had solid facts to go upon, 2 however
inaccurate may have been their explanation of these facts.
Lightning rods, and the buildings they were intended to
protect, have unquestionably often been the scenes of
explosions ; and in many cases it could not have been
unreasonable to have treated the rods themselves as the
causes of these disasters.
At all events, there was the fact of the explosion ; and it
is only in the nature of things that the sufferers from the
injuries caused by it should, not infrequently, have con-
sidered that any explanation of it, however, scientific, and
however much the rods were exonerated, was but a poor
consolation to them, should have declined to have anything
more to do with such contrivances, and should have
advised their acquaintances to act in the same way.
The knowledge of rods being frequently struck is
probably the reason why, in this practical country, they
are by no means universally adopted on buildings which
present elevated features that might reasonably be con-
sidered to entitle them to the chance of obtaining whatever
advantage might be desirable from the employment of
such apparatus, e.g. country churches with towers, many
of which are without rods.
The conflicts of opinion amongst the advocates of
rods 3 may probably have also contributed to the develop-
ment of the general indifference on the subject which has
existed amongst Englishmen generally, but especially
amongst English architects.
1 I. E 1. II. A 17 ; G 3, 4, 7, 8, 46.
2 II. A 16, 27, 3335 ; G 6. VIII. C 1, 2.
3 I. C [46, 48] ; E [4, 9] ; [E 1, II. G 15] ; II. B [20, 27], [31, 53],
[39, 60] ; C [17, 35], [29, 46] ; [C 34, E 12] ; [D 22, G 49] ; E [5, 40 J,
[29, 38] ; [E 16, G 45]; E 41 ; G [26, 39], [16, 55], [42, 54] ; G 36 ;
[G 32, B 46].
M 2
244 LIGHTNING.
VIII. A d.
(d) Diverse Systems of Application.
At the present time there are two schools amongst light-
ning authorities. 1
The chief school, comprising the great majority of
physicists and engineers, adopts the principle, prominently
expressed in Sir William Snow Harris's works, of em-
bracing the building to be protected in a network of metal
so as to bring it as nearly as possible into the condition of
a metal building. 2
In this system, the stalk of the rod is metallically con-
nected to all the metal surfaces on the building, and is
moreover supplied with branches in the form of metal
bands which proceed along the roof ridges, gable ends,
eaves, valleys, and salient outlines of the upper part of the
building generally. 3
The stalk is thus only the backbone of the protective
system of the building ; and the object of this system is,
through the conductive power of the metal, to afford an
easy passage to the root of the rod (i.e. to earth) for a
lightning discharge that may strike any part of the
building from above. 4
During the last few years this system has received
further elaboration from eminent electricians by an increase
of metal both as regards the number of points, and also as
regards the extent and ramification of the roots. 5
The plan recommended and practised by the school of
the minority is to place the rod well clear of any existing
metallic surfaces, to insulate the stalk at the necessary
points where it is fixed to the building, and to make its
course to the earth as direct as possible. 6
The metallic connections with the stalk, and the
1 II. E 28, 29. * II. E 42 ; G 19.
3 II. B 5, 21, 40, 45, 56; E 13, 1619, 25, 26, 28, 31, 36, 38; G
37, 45, 50. IV. 19. * VI. B a.
3 II. B 18, 29 ; C 19, 22, 36, 49 ; D 9, 12, 52, 54 ; G 19.
6 IV. 1, 3, 28, 30, 31, 37, 3941, 43, 45, 47, 48.
THE PRESENT SYSTEM OF LIGHTNING RODS. 245
VIII. B.
branches therefrom, are held by these dissenters to be
superfluous when the rod is in good order, and dangerous
when it is not. 1
(B.) COMMENTS ON THE THEORY AND PRACTICE or
LIGHTNING EOD DEFENCE.
The advantages afforded by a lightning rod appear to
be summed up in the fact that, if it be in good condition, it
tends by means of its point to furnish an outlet for any
charge that may collect at the particular parts of the
ground in contact with its root.
In the case of a building, if the surface of the ground
around it have good collective qualities, and constitute one
collector, 2 doubtless, if the root pierce it anywhere, it would
tap the whole of it ; and thus the rod would help greatly
to defend the building from explosion.
Even then, however, the protective power of the rod is
apt to be modified by reason of the fact that ordinary
ground (moist earth) is not an accumulator of electricity
like metal, 3 and that an appreciable amount of time must
be required for the whole of a charged strip of ground
around a building, or an elevated feature of a building, to
empty itself through the rod ; and unless the root com-
pletely permeates this ground and envelopes the building
or its prominent feature, the potential of the charge of the
ground at the parts of the base not thus embraced is
liable to increase at a greater rate than that at which the
charge is drawn away by the action of the point ; and thus,
in spite thereof, explosion may ensue.
The usual practice, however, is to lead the root of a rod
directly away from the walls, 4 principally in order the
better to obtain moisture ; 5 hence it follows that the rod
1 II. E 29. 2 V. A 9. 3 vi. D .
* III. 56. 5 II. D 1, 12, 13, 15, 20, 32, 35, 52, 64.
246 LIGHTNING.
VIII. B a.
taps a considerable extent of ground which has nothing to
do with the protection of the building.
In the case of a ship afloat, the iron or coppered bottom
of the hull forms an excellent root, completely covering the
ship's contact with the sea, and tapping the latter all round
the ship's sides ; and if the stalks running up her masts
and rigging be efficiently connected to this root, as they
usually are, the ship's system of defence, qud her power of
eliciting the earth's electricity that may collect around her,
and thus of preventing explosion, is by no means a bad
one, and probably greatly superior to the defence given by
lightning rods to the great majority of buildings and con-
structions ashore. 1
The principal disadvantages appertaining to lightning
rods attached to buildings appear to be as follows, viz. :
(a) The exposure of elevated metallic surface fur-
nished by them.
(5) Their costliness.
(c) The sources of failure to which, after erection,
they are liable.
(d) Their tendency to disfigure the appearance of
buildings.
(a) The Exposure of Elevated Metal.
The elevation of the rod's point above the ground is pro-
bably due to some extent to the generally accepted maxim
that a conical space, the extent of which depends on the
height of the rod, is protected by it. 2
When a rod is well connected to the ground it constitutes
a local plate, and the exposure of elevated metal must
always be a great disadvantage ; for however well pointed
this metal may be, and however thoroughly it may tap the
ground, it must always be impossible to estimate whether
i II. A 30 ; B 615 ; G 23. 2 II. G 1, 21, 35, 41, 47.
THE PRESENT SYSTEM OF LIGHTNING RODS. 247
VIII. B a.
its tapping powers are on a par with its accumulative pro-
perties ; and should the latter prevail, explosion will occur,
and we can never foresee with certainty whether it will
spring from the point (effecting, perhaps, no harm beyond
blunting or fusing it), or from some lower portion of the
stalk, or even from the whole of it at once ; and it is clear
that in the latter two cases the discharge may take a direc-
tion which may cause great injury to the building. 1
Experience tells us that these " lateral discharges" or
deviations of the explosion from the line of the rod are by
no means rare occurrences. 2
In cases where the piece of ground surrounding a build-
ing does not form one collective surface, but is broken up
into several distinct collectors by means of intervening
insulative or slowly collecting portions, it is evident that,
under the present system of disposing a rod's root, there
may be, close to the feature expressly intended to be de-
fended, patches of surface which are not in any degree
tapped by the rod.
Thus, in ground at no great distance from the rod a
charge may accumulate and explosion may ensue ; but now
the rod's stalk, owing to its metallic substance, extent, and
elevation, becomes very liable to be embraced in the ex-
plosion's line of least restraint, in which case the discharge
probably leaps from the ground to the stalk over the sur-
face of the building.
The stalk then, although itself a local plate, has acci-
dentally acted as a local dielectric to the adjacent charged
ground to which it is not connected, and, instead of having
protected the building, has positively attracted danger to
it ; and this, although the apparatus may have been in a
thoroughly efficient condition. 3
When a rod does not " make good earth," i.e. when it is
not electrically connected to the ground, it constitutes an
VII. B c, d; G e. VIII. C 6. 2 II. B 26, 46. VIII. C 11.
3 VII. B g. VIII. C 7.
248 LIGHTNING.
VIH. Ba.
elevated local dielectric to all the ground below and around
it; and experience fully shows that, in this condition,
it is very liable to cause explosion and to be broken in
pieces. 1
Thus the stalk of a rod, whether acting as a local plate,
or as a local dielectric, is a source of unmitigated danger ;
and this is in all cases considerably enhanced if it be formed
of copper instead of iron ; for the former accumulates elec-
tricity six times faster, and attracts explosion six times
more powerfully than the latter. 2
If the stalk of a rod be carried up inside a building, as
it occasionally is to some extent, 3 a great part of the
danger due to the exposure of metal would be obviated ;
but, on the other hand, there would be some risk, whilst
the elevated pointed terminal remained outside, of the in-
terior of the house being injured by explosions.
It would appear that Franklin's original intention actu-
ally was to carry up the stalks inside buildings, and that
the practice was adopted on the Continent, but was soon
abandoned. 4
The fact of this abandonment, and of the almost uni-
versal system that has since remained in force of erecting
rods outside buildings, seems to be a fair witness of an
almost unanimous feeling that rods certainly attracted ex-
plosion however much they might afterwards annul its
effects. 5
The connections between the stalk and the metal surfaces
on the building, as also the branches from the stalk along
the ridges, eaves, gables, or other salient outlines of the
building, of course add considerably to the amount of
elevated metal exposed.
On board ship, the comparative danger from the stalk is
probably less than on buildings, since the masts, yards,
and rigging of ships always contain a considerable amount
1 VII. B /. VIII. C 8, 5 $. 2 VI. D a.
3 IV. 10, 13, 20, 42. * II. E 37. 5 II, G 8.
THE PRESENT SYSTEM OF LIGHTNING RODS. 249
YIII. B b.
of metal in an elevated position, and the extra metal due
to the rod may therefore be relatively less felt.
(i) The Costliness of Rods.
The principal practical causes of expense in the first
cost of a lightning rod appear to be four in number,
viz. :
(1.) The use of copper.
(2.) Expensive points.
(3.) The connections and branches of the stalk.
(4.) The extension of the root in search of moisture.
(1.) The use of copper^ in lieu of iron, the material em-
ployed by Franklin, 2 appears to have been adopted mainly
for the reason that, conductivity for conductivity, one is as
cheap as the other, and that copper is the less corrodible
of the two. 3
The employment of copper rods has been mainly confined
to these islands, 4 and seems to have been brought about
chiefly through the influence of the late Sir William Snow
Harris, to whom the metal recommended itself over iron,
for employment on board H.M. ships. 5
For the defence of ships the use of copper was gradu-
ally extended to that of powder magazines, 6 and other
buildings. 7
Copper may doubtless have been a convenient metal for
adapting ships* masts to act as lightning rods, but there
seems to have been no adequate scientific or practical
reason for introducing the metal for the protection of con-
structions on land ; 8 for iron rods, like any other forms of
iron used on the exterior of buildings, could always have
1 IV. 1 5, 811, 13, 1826, 28, 29, 31, 3336, 3848.
* II. B47. 3 II. B 31_35, 36.
4 II. B 55, 67 ; C 50. 5 II. B 5, 1113, IV. 44.
IV. 19. 7 II. A 31 ; B 40. 8 II. G 22,
250 LIGHTNING.
YIII. B I.
been preserved from corrosion (before the galvanising
process was known) by means of painting or tarring. 1
The reception of the idea of using copper on buildings
has led to unnecessary expense and danger ; for the ele-
ment of slenderness in rods of any material has generally
been looked upon with disfavour ; 2 and it is probable that
in almost every instance where a copper rod has been em-
ployed, an iron one of the same dimensions would have
answered the purpose equally well ; whilst, qua exposure
of metal, it would unquestionably have been far less dan-
gerous. 3
Indeed, for all that is known to the contrary, an iron
rod of the smallest practicable dimensions has a power for
tapping any portion of earth it may be rooted in immensely
in excess of what is needed to prevent that earth from
accumulating potential.
Till good cause is shown why iron is inefficient for the
purpose, the use of copper, independently of its intrinsic
disadvantages, 4 would seem to be in the same category as
that of silver and gold, and to be objectionable simply be-
cause it is expensive. 5
(2.) Expensive points. The prevalent employment on
rods of pointed upper terminations made of copper, platina,
or silver alloy, must of course constitute sources of ex-
pense.
The points of rods have been found to be liable to cor-
rosion by the atmosphere and to fusion by lightning ; and,
as they are in such elevated positions that they cannot
readily be visually examined or repaired, it has been
thought that if they were formed of less corrodible or harder
materials such as those mentioned, they would be less
likely to need such examination and repair. 6
The use, then, of these materials for the formation of
* II. B 55. * II. B 5, 33, 40.
3 II. B 27, 30 ; E 6. * II. B 22, 35, 42, 53.
5 II. A 31 ; B 50. VI. D a. 6 II. C 10, 18, 20, 41, 47.
THE PRESENT SYSTEM OF LIGHTNING RODS. 251
Yin. B i.
points is an expensive palliative rather than a sound remedy
for the impossibility of constantly observing them and
keeping them sharp.
Another costly arrangement is the brush or multiple
point that is now frequently used. 1
This brush is a cluster of three or more points, instead
of a single one, at the end of the stalk ; and the principal
reasons for its use appear to be that there is a greater
chance, among a number of points, of one remaining sharp,
and that even if they all become blunted, still a number of
blunt points is better than only one. 2
Here the remedy appears to be not only imperfect and
expensive, but also dangerous, for metal is thereby con-
centrated in the most elevated position.
(3.) The metal lands forming connections between the stalk
and the metallic surfaces on the exterior of a building, and
embracing its ridges, eaves, gables, and other prominent
outlines, are clearly arrangements which, especially when
formed of copper, increase considerably the cost of the
rod. 3
(4.) The extension of the root becomes a source of expense
where, as frequently happens, there are no underground
metal pipes near the building, and where there is no water
or moisture in th vicinity.
It is customary to utilise as the roots or " earths " of
lightning rods the gas or water mains of towns, on account
of the large area of metal in contact with the ground
afforded by these pipes, and of the facilities considered to
be furnished thereby to the lightning discharge for dis-
persing itself harmlessly in the earth's reservoir. 4
In the country the roots of rods are usually led into the
the nearest well, sheet of water, or permanently moist
ground. 5
1 IV. 3, 21, 2932, 39, 41, 42, 47, 48.
2 II. C 68, 19, 22, 32, 36, 49. 3 n. E 36. IV. 19.
* II. D 1, 12, 13, 15, 32,55.
5 II. D 7, 1113, 15, 2123, 26, 27, 34, 36, 40, 43-45, 48, 49, 5154.)
252 LIGHTNING.
VIII. B b.
If permanent moisture, however, should not exist near
country buildings, the plan advocated is to enclose the
roots within trenches filled with coke or charcoal embers,
and to extend these trenches in every direction as far as
practicable, so as to obtain as much temporary moisture as
possible, and by means of a large area of root to compen-
sate for the want of such a receptive state of the ground
as alone is afforded by permanent moisture ; moreover,
rain water from the building is, where such a plan is
feasible, to be led over the sites of these trenches. 1
In the country, then, the roots of lightning rods, when
arranged according to modern ideas, would frequently be
costly ; but it is obvious that, according to the theory on
which they are disposed, they may also frequently be ineffec-
tive, however expensive and troublesome the laying of
them proved to be ; for buildings are constantly erected on
dry and rocky sites so far removed from moisture that the
excavations necessary to bring the roots thereto are out of
the question.
In such cases, so far as can be seen, it is admitted by
their advocates that lightning rods cannot be relied on.
Nothing can show more clearly how little the preventive
power of the rod's root and point is thought of than the
fact that such a practice as that of seeking moisture for the
root is actually nearly everywhere in force.
If it were allowed that in protecting the building the
function of the rod, or even one of its functions, was to
tap and rid the ground of a certain element, it is incon-
ceivable that the presence of ground full of the conditions
for collecting this element should be considered a sine qua
non for the due protection of the building. 2
If we wish to defend a place from an enemy we do not
usually consider the presence of conditions favourable to
an attack as essential to the due protection of the place.
On the other hand, if it be held that lightning descends
II. D 2, 9, 10, 13, 15, 28, 31, 35, 46. * VII. A b t c.
THE PRESENT SYSTEM OF LIGHTNING RODS. 253
VIII. B b.
from heaven, strikes the rod, is conducted by it into the
earth's reservoir, and needs a sympathetic or receptive
state on the surface of that reservoir in order that it may
disappear therein quietly and without obstruction, 1 then
the practice we have mentioned would seem strictly rational
and suitable.
Apparently a lightning discharge is usually treated as if
it were a telegraph current, which, as we know, in order
to complete its circuit without a return wire, is in need of
"good earth."
The telegraph " earths" are accordingly either formed
of gas or water mains, or of metal plates buried in earth
which is either naturally, or artificially, moist. 2
It seems to have been considered that an analogous
course of treatment was necessary for a lightning dis-
charge, 3 in order, apparently, that it should complete its
circuit, i.e. vanish, as quickly as possible.
It is only within the last thirty years that a practice,
previously in vogue, of constructing small masonry tanks,
kept full of water, to receive the roots of rods, has been dis-
continued : 4 what the function of the rod's point was con-
sidered to be under these circumstances it is difficult to
imagine.
We consider, then, that the attachment of rods to gas
and water mains is simply giving these mains an addi-
tional, and generally unnecessary, outlet for the electricity
tapped by them throughout the town ; and that the build-
ing against which the rod thus rooted is fixed is more ex-
posed to injury from lightning than the other buildings of
the town.
And, in the case of a rod whose root is laid in rivers, or in
wells, or in water or moisture of any kind, not immediately
contiguous to the construction, we maintain that the latter,
so far from being protected, is merely being utilised to tap
1 II. G 48. 2 II. D 42. 3 VI. B a.
* II. D 3, 33, 37, 38. III. 43, 44. IV. 19.
254 LIGHTNING.
VIII. B C.
the electricity of this water or moisture, and that the rod
is a distinct source of danger to it.
(0) The Sources of Failure to which Rods are liable.
The rod having been erected according to the best scien-
tific advice, then comes the question of the disadvantage
due to the various elements in its construction which ex-
perience has proved are apt to render it a failure qua the
purpose for which it was designed.
The sources of failure inherent in rods after their con-
struction, as stated by their advocates, are as follows,
viz. :
(1.) The stalk being of insufficient sectional area. 1
(2.) Bad joints along the length of the stalk, or
between the stalk and the root; or deficient
connection between the stalk and the metals of
the building. 2
(3.) Alterations made in the arrangement of the
metals of a building after the rod has been
erected. 3
(4.) Blunt points. 4
(5.) The root, or earth connection, when tested with
a galvanometer, displaying too great a resist-
ance. 5
( 1 .) As regards sectional area the opinions of authorities are
conflicting : some say that a rod of small sectional area has
advantages, whilst others doubt if it is better than none at
all. 6
It is clearly a considerable disadvantage to the present
system of rods that, on such an important question, doctors
should disagree.
1 VIII. C 5 a. II. F 68. VIII. C 5 ft.
3 VIII. C 5 y. * II. F 6 ; G 18.
* II. F 14. VIII. C 5 S.
6 II. B 16, 20, 23, 2730 ; G 16, 17, 55.
THE PRESENT SYSTEM OF LIGHTNING RODS. 255
VIII. B e.
(2.) Sad joints along the stalk's length are hardly so likely
to occur in these days as of yore ; for the kinds of stalks
mainly used for the protection of buildings in the present
day are wire ropes, 1 needing no joints such as those re-
quired in the solid bars, bands, tubes, and chains, which
were formerly employed. 2
The action of the wind on the more or less unsupported
pointed terminals projecting above the building is, how-
ever, with all kinds of rods, very likely to work loose the
connection between these terminals and the supported por-
tion of the stalk below. 3
The possible disconnection underground of the stalk
from the root is a source of failure that seems always
liable to occur on account of the electrolytic action set up
partly by the constant flow of a current from the earth
through the rod, owing to its tapping powers, and partly
by the moisture in the ground : by this action the metal
appears to be gradually eaten away near the surface. 4
Another cause of disconnection between the stalk and
the root happens when the former is of copper, and the
latter (as it usually is) of iron : in this case galvanic action
is apt to be set up by the contact of the two metals in the
presence of moisture, and the iron is decomposed. 5
Want of connection between the stalk and the metals of
the building is a reason that has been advanced for the
failure of rods. 6
The remedies that have recently been proposed for the
existence of bad joints and disconnections are the constant
inspection of the rod, and the periodical testing of its con-
tinuity by means of a galvanometer. 7
(3.) Alterations made in the positions of the metals of a
1 IV. 15, 7, 8, 21, 22, 24, 28, 29, 31, 3336, 3943, 4548. II.
B 1, 15, 17, 27, 30, 44, 59.
2 II. B 69, 12, 25, 37, 41, 48 ; F 7. IV. 6, 920, 22, 23, 2527,
30, 32, 37, 38, 44. 3 II. G 51 ; F 6.
* II. D 8, 16, 18, 19 ; F 8. IV. 25. 6 II. B 38 ; D 30, 39.
6 III. 129. 7 II. F 15, 914.
256 LIGHTNING.
VIII. B e.
building, after a rod has been erected, have been found to
vitiate its usefulness ; and it is quite conceivable that such
metals have in some instances been placed in positions
where they have formed, in conjunction with part of the
stalk, lines of least restraint from the ground, thus causing
the stalk to form an accidental local dielectric, and effect-
ing injury to the building. 1
It would appear necessary then that, at the proposed
inspections of the rod, the positions with regard to it of all
metals, both inside and outside the building, should be
examined.
(4.) Blunt points. The only effective remedy for the
points becoming blunted would appear to be visual ex-
amination of them ; but this would be quite impracticable
in the case of church spires and tall chimney-stalks with-
out the aid of scaffolding or other expensive appliances.
(5.) Resistance of the roofs earth contact. The last and most
important of the sources of failure mentioned is that alleged
to be due to the rod " making bad earth."
It is held by lightning engineers that a rod is untrust-
worthy, i.e. that it cannot be depended on to lead away
harmlessly the lightning discharge striking it, 2 if, on its
"earth" being tested by a battery current of certain
strength, a resistance above a certain standard is recorded
on the galvanometer. 3
It is not stated what this standard is, nor how it has been,
or can be, determined with accuracy ; 4 but, allowing that this
point can be, and has been, settled, it is evident that great
expense may have been incurred, when the rod was erected,
in bringing its root to what might (taking one year with
another) be fairly reckoned as permanent moisture ; yet,
should drainage operations have taken place in the adja-
cent ground, or should a period of drought supervene, and
should this moisture be reduced to such a degree that the,
II. G 53. III. 158. 2 VI. B a.
II. F 1, 4, 9, 14. II. F 15.
THE PRESENT SYSTEM OP LIGHTNING RODS. 257
VIII. B d.
galvanometer standard of resistance would be exceeded, then
apparently the rod would be useless until remedial measures
of some kind had been taken. 1
Supposing, however, that at a testing the resistance of
the " earth " should be found to exceed the standard, the
course to be pursued seems by no means clear. How are
we to remedy the evil ? Are we to open the ground over
the course of the root, and to examine the latter visually to
see if anything is at fault with it ? Or are we to presume
that the fault is altogether with the state of the ground ;
and if so, by what practical means are we to render it, qud
the object we have in hand, more moist ?
Altogether, the rule laid down for bringing the roots of
rods into moist earth, and for testing them periodically as
to their efficiency, is apparently surrounded with so much
difficulty and uncertainty that, alone, it would seem to con-
stitute a fatal drawback to the employment of lightning
rod defence in accordance with modern views.
Even if this system should result in obtaining a pro-
tective apparatus always to be relied on, the disadvan-
tage due to the trouble and expense of the periodical test-
ing by electricians would still remain. 2
(d) The Tendency of Rods to Disfigure Buildings.
The minor disadvantage due to the tendency of rods to
disfigure the appearance of constructions is one that chiefly
applies to churches, edifices containing some architectural
adornment, and monuments or columns ; and it cannot be
said to apply at all to such constructions as powder maga-
zines and chimney-stalks.
The features to which rods are affixed are always the
most prominent ones of the building ; hence it is difficult
to conceal the rod, and its visibility is enhanced when
brush points or insulators are employed.
Owing, therefore, to the conspicuous positions they
1 II. D 47, 49, 54. 2 II. F 14.
258 LIGHTNING.
VIII. 1 a y.
occupy, and to their incongruity with their architectural
surroundings, rods are apt to mar the appearances of
buildings. 1
Of course this disfigurement is reduced considerably
when the stalk is carried up inside the building ; but, as
we have stated, this course is an unusual one, and, even
when it is adopted, the 'pointed terminal may be a very
unsightly object, as, e.g. in the case of the Duke of York's
Column in London.
(0.) ANALYSIS OF LIGHTNING INCIDENTS CONNECTED
WITH HODS.
Attention will now be drawn to such of the incidents
mentioned in Chapter III. as record that lightning rods,
or the constructions they were designed to protect, were
struck by lightning, or that rods were instrumental in pre-
venting explosions. (N.B. The nos. marked (s) are cases
of ships, and those marked c are instances of copper rods.)
(1.) EODS STRUCK. (45 CASES.)
(a) No damage done. (13 cases.)
Nos. 8,
22,
56,
69 c, (),
70 c *
78,
79,
99 c,
100 c, (*),
101 c, (s),
102 c, (s),
(ft) Only the Rods damaged. (11 cases.)
Nos. 5 (s), 46, 64 (s),
6 c, 49, 65 c,
44, 59 <?, 89 c,
120.
92,
156 c.
(y) Both Rods and Constructions damaged. (15 cases.)
Nos. 19,
21,
43,
47,
55 c,
58,
86 c,
91 c,
103,
108,
128
131
150,
153,
179.
IV. 1, 3, 6, 14, 15, 18, 24, 25, 2729, 34, 41, 47.'
THE PRESENT SYSTEM OF LIGHTNING RODS. 259
VIII. C 1, 25 a 7.
(8) Constructions damaged, but not the Rods. (6 cases.)
Nos. 72 c, (*), 73, 104 c, (s), 114, 118 c, 157 c.
(2.) CONSTRUCTIONS STRUCK, BUT NOT THE RODS. (16 CASES.)
(a) Constructions damaged. (II cases.)
Nos. 71 0, (*),
74,
75 (*),
105,
110,
127,
130 c,
147,
155,
158,
160.
(ft) Constructions damaged and persons injured. (2 cases.)
Nos. 129 c, 134 c.
(y) Persons at or near the Constructions killed or injured.
(3 cases.)
Nos. 45, 82, 115.
[NOTE. In No. 82 the rod was probably struck, though the record
specifies the magazine.]
(3.) CONSTRUCTIONS WITHOUT RODS, DAMAGED, CLOSE TO
OTHER CONSTRUCTIONS WHICH HAD RODS, BUT
RECEIVED NO INJURIES. (2 CASES.)
Nos. 48, 181.
(4.) BUILDINGS STRUCK BEFORE BEING SUPPLIED WITH
RODS, BUT NOT SUBSEQUENTLY. (4 CASES.)
Nos. 57, 77, 80, 81.
(5.) CAUSES TO WHICH THE FAILURES OF RODS HAVE BEEN
ATTRIBUTED BY AUTHORITIES.
(a) To insufficient sectional area of Rod. (10 cases.)
Nos. 5, I 56, I 59, i 65, | 131,
19, 58, 64, I 118, 134.
((3} To bad joints or deficient connections. (4 cases.)
Nos. 5, 114, 129, 131.
(y) To the metals of the building. (2 cases.)
Nos. 45, 158.
260
LIGHTNING.
VIII. 05 8, c; 610.
(8) 1
7 o lad earth.
(17 cases.}
Nos. 43,
86,
118,
131,
156,
44,
89,
127,
134,
157,
55,
91,
128,
155,
179.
64, 115,
(c) To the Rods "being "not so perfectly applied as they ought to
have been" (1 case.}
No. 73.
(6.) EODS WHICH PROBABLY ACTED AS LOCAL PLATES.
(22 CASES.)
Nos. 6,
66,
72,
79,
99,
102,
120,
8,
69,
73,
82,
100,
104,
150,
21,
70,
78,
92,
101,
108,
153.
49,
(7.) EODS WHICH PROBABLY ACTED AS ACCIDENTAL
DIELECTRICS. (9 CASES.)
Nos. 5, I 22, I 56, I 59, I 114.
19, I 47, I 58, I 65, |
(8.) EODS WHICH PROBABLY ACTED AS LOCAL DIELECTRICS.
(15 CASES.)
Nos. 43,
44,
46,
Nos.
55,
64,
86,
89,
91,
103,
118,
128,
131,
156,
157,
179.
(9.) ENDS or EODS FUSED.
5,
55,
128,
6,
64,
150,
21,
92,
153,
46,
103,
156.
49,
(10.) MECHANICAL INJURIES TO EODS.
Nos. 44,
58,
92,
46,
59,
108,
47,
65,
131,
49,
86,
179.
55,
89,
THE PRESENT SYSTEM OF LIGHTNING RODS. 261
VIII. C 11, 12.
(11.) DEVIATIONS OP THE EXPLOSIONS FROM THE BODS.
Nos. 43,
55,
58,
86,
91,
103,
114,
128,
131,
150,
153,
179.
(12.) NOTES.
In regard to the 13 cases of Group (1), in which the
rods were struck, but it so happened that no damage was
occasioned to the constructions, if the theory be sound that
a rod is placed on a building in order to waylay the
lightning in its supposed descent, 1 and to afford it an
easy channel to the earth, 2 these incidents can only be
looked upon as illustrations of the success of the rods.
But if the theory which we have striven to prove be
correct, and if the true function of lightning rods be to
prevent explosions occurring at all, 3 then unquestionably
these 13 cases, equally with the 32 others of Group (1), in
which the rods were struck, and damage also was done,
are clear instances of failure ; for every one of these
45 instances is a proof that, instead of preventing explo-
sion, the rod caused it.
Let us put the matter in another form. If the rods had
no share in causing these explosions, why were they
struck ? 4 Is it not manifestly in accordance with elec-
trical law that no single portion of an exploding condenser
can exist that has not had its share in determining explo-
sion ? 5
If the views we have upheld be sound, it is clear that
nothing in nature can be struck by lightning without
having first caused lightning to strike it.
1 VI. B a. 2 II. G 5, 6, 31, 39, 48.
3 II. C 30; G 40, 56; E 27. * II. G 6.
* V. B 11.
262 LIGHTNING.
vin. c.
In the 16 incidents of Group (2), where the rods were
not struck, but the buildings or persons in them were in-
jured (the special cases of Nos. 74 and 115 excepted), the
rods, according to the generally received views, must be
considered as having failed to exercise their supposed pro-
tective influence; but if they be viewed in the light in
which we have been treating them, they cannot be alto-
gether treated as failures ; for they evidently protected the
building to the best of their ability by preventing explo-
sions occurring at the places tapped by their roots ; whence
it followed that they themselves were not struck, and that
the scenes of the explosions were distant from them and
probably outside the influence of their roots.
Here, undoubtedly, the beneficial power of the roots and
points overbore the baneful accumulative action of the
stalks ; and the rods were successful so far as the disposi-
tion of their roots permitted.
Out of the 61 cases comprised in Groups (1) and (2), the
following, by reason either of their instructive character or
of the fulness of the information that has been procurable
concerning them, appear to be well worthy of attention,
viz. :
Buildings.
No. 43. Milan Cathedral.
44. Genoa Lighthouse.
47. Bayonne Powder Magazine.
49. Signer Melloni's house.
55. Normanhurst Court.
56. The Sorbonne.
82. Glogan Powder Magazine.
86. Warehouse near Victoria Station.
114. Barrackpore Barracks.
115. Buys' house at Natal.
118. All Saints' Church, Nottingham.
128. Rostall Church.
129. Bruntcliffe Colliery Powder Store.
130. Cromer Church.
131. Laughton Church.
134. Wrexham Church.
THE PRESENT SYSTEM OF LIGHTNING RODS. 263
VIII. C.
No. 155. St. Mary's Church, Genoa.
156. Alatri Cathedral.
157. Clevedon Church.
160. Compton Lodge, Jamaica.
179. East London Powder Magazine.
Ships.
No. 5. Packet Ship New York.
65. H.M.S. Dublin.
69. H.M.S. Beagle.
71. H.M.S. Endymion.
72. H.M.S. Etna.
104. H.M.S. Eaeer.
Of the above cases, Nos. 49 and 56 are very remarkable,
as clearly showing the power of rods to attract lightning ;
and especially No. 49, which Arago has recorded with
some circumstantiality.
Another noteworthy case is No. 156 ; firstly, because the
incident narrated is shown to be the fifth occasion since
the rods were erected, i.e. in eight years, that one or other
of them had been struck ; secondly, because, in the case in
question, the attractive power of the rod is shown by the
fact that the explosion actually cut its way horizontally
through 1 1 yards of hard ground in order to get at it ;
thirdly, because the root appears to have shared with the
stalk its function of local dielectric. The damage at the
Alatri Fountain was probably caused by a simultaneous
explosion thereat.
The cases in Group (3) are to some extent evidences of
the usefulness of rods ; for in these cases explosions hap-
pened at constructions not defended by rods, close to a
number of others which were so protected ; but none of
these protected buildings or their rods were struck.
The facts related in the 4 cases that constitute Group (4)
are important, as showing that the buildings in question
had been repeatedly struck before rods were applied, but
never afterwards ; and this would seem to testify to the
benefit that arose from their presence.
264 LIGHTNING.
VIII. D.
D. SUMMARY OF EEMABKS ON LIGHTNING BODS.
The advocates of rods in their present form appear to
maintain that any danger due to the attractive influence of
the stalk is practically neutralised by its conducting power,
and that these characteristics do not hinder the rod from
faithfully performing its preventive duty : in other words,
they hold that the rod, through its root and point, unceas-
ingly tries to prevent lightning from coming to the build-
ing, and that if it should herein be unsuccessful, its stalk
becomes useful, [inasmuch as it furnishes, firstly, a pro-
minently attractive object by which the descending light-
ning l is intercepted from striking the building, and,
secondly, a good conducting channel by which the discharge
is led harmlessly into the ground. 2
But if we once entertain the notion that lightning springs
from the ground 3 and cannot be intercepted or conducted,
the raison d'etre of the stalk ceases, and our course becomes
limited to preventing the development of those conditions
which go to form lightning ; and, according to all expe-
rience, and to what is now admitted by lightning engineers,
stalks and elevated metals of any shape on the exterior
surfaces of buildings are certainly among these condi-
tions. 4
According to our views, then, there is no sound founda-
tion for the existence of the stalks of lightning rods, and
their presence is an unmixed source of danger and ex-
pense.
It may be urged by the advocates of lightning rods that,
during the one hundred and thirty years that have elapsed
since they were invented, the vast majority of buildings to
which they have been affixed have not been harmed by
lightning, and that they can hardly be expected to abandon
this time-honoured system unless some practical proof of a
better one be given.
1 VI. B a. * II. C 4345 ; G 44. 3 VI. B b.
* II. G 14, 15, 2527. I. E 9.
THE PRESENT SYSTEM OF LIGHTNING RODS. 265
VIII. I).
In reply, however, it may be asked, would these buildings
ever have been injured if the rods had not been present?
It may even be asked, how can we know that these build-
ings did not receive their immunity in spite of their rods ?
As regards practical proof, it is obvious that, until we
are able to forge thunderbolts, the efficacy of any defensive
measures devised to prevent them cannot be tested.
Our guide, then, in the matter of lightning engineering
must still be, as it always has been, theory. Now we are
told on good authority that theory is " a sort of intellectual
contrivance for representing to the mind the order and
connection subsisting between observed phenomena." 1
The marshalling of observed actions and incidents in
connection with lightning is, therefore, what we must rely
on as the basis of our system of protective measures.
In conclusion, we may sum up our opinion on the pre-
sent system of lightning rods as follows :
(1.) Owing to their roots and points they have a
tendency to protect the constructions (and espe-
cially the ships) to which they are affixed ; and
they frequently have done so. 2
(2.) Owing to their stalks they have a tendency to
injure the constructions to which they are at-
tached ; and they constantly have done so. 3
(3.) When applied to the defence of buildings their
roots are unscientifically arranged. 4
(4.) Their costliness* and uncertainty act as deter-
rents to the adoption of measures for obtaining
defence from lightning at all, 5 and are espe-
cially injurious to the interests of the poorer
classes.
1 I. A 3. 2 II. B 13 ; G 2, 10, 20, 23, 34.
3 VIII. A e. * VIII. B. 5 vi U. B, b, c.
* " Sir William Thomson, at the meeting of the British Association
at Aberdeen, said, 'If I urge on Glasgow manufacturers to put up
lightning rods, they say it is cheaper to insure than to do so.' " Report
of Lightning Hod Conference.
IX.
fart ML
PRACTICAL MEASURES ADVOCATED FOR
THE DEFENCE OF LIFE AND PROPERTY
FROM THE EFFECTS OF LIGHTNING.
CHAPTER IX. PRACTICAL MEASURES
ADVOCATED.
WE have now arrived at that part of our treatise where it
becomes necessary to show how the theories we have
advanced can be put into practical shape.
The subject of the best means of defending life and
property from the action of lightning appears to divide
itself into three distinct phases, viz. :
(A.) The defence of large areas, such as countries,
districts, and towns.
(B.) The defence of constructions, e.g. buildings,
mines, and ships.
(C.) The defence of individuals.
The great end of any defensive measures should un-
doubtedly be to save life ; and the defence of buildings and
ships is of course a valuable means to that end ; but the
protection of property, qua property, is also necessarily of
much importance.
It will be evident from the views upheld in Part II. that
the great principle which we advocate to be carried out
to the utmost extent in the defensive measures to be
adopted in dealing with thunderbolts, is that of prevention.
PRACTICAL MEASURES ADVOCATED. 267
IX. A. a.
The three phases which we have enumerated will now
be dealt with separately.
(A.) THE DEFENCE OF LARGE AREAS.
(a) The Defence of Countries and Districts.
It is evident that any action taken with a view of pre-
venting or diminishing the occurrence of thunderbolts in
whole regions cannot well be undertaken by any other
agency than the Government of the country.
The first step in such a course of action would appear to
be the scientific investigation of each separate instance of
death or injury occasioned by lightning, and the accurate
record of the results of such investigations.
Thus each incident injurious to the community inflicted
by thunderbolts would form the subject of Government in-
spection and report, on a system somewhat analogous to
that now in force in England for inquiring into the causes
of railway accidents, or of those due to the manufacture,
storage, and transport of combustible materials.
So soon as facts had accumulated to a degree to warrant
the assumption of some laws as to the manner in which, in
the country in question, thunderbolts appeared to guide
their action, then would probably be the time for the
Government to consider the advisability of some definite
course of operation as regards either the whole country, or
any particular district or province whose circumstances
would appear most to require such treatment.
It is impossible to forecast what direction this more
detailed action of Government might take ; but it is quite
conceivable that great public benefit would ensue to certain
localities from the trial of some inexpensive general
measures which the experience resulting from the records
of lightning incidents might show to be worthy of
experiment.
No kind of lightning apparatus (however simple) for the
defence of individual buildings could possibly compare in
advantages with the adoption of a policy on the part of
N 2
268 LIGHTNING.
IX. A a.
the authorities calculated to prevent, so far as possible, the
occurrence of thunderbolts within the whole region ; and by
110 surer method could life and property be more effectually
preserved.
We believe that the amount of light that would be
thrown on the action of lightning from the mere scientific
inspection and record by authority, for a few years, of the
thunderbolt incidents that should take place during that
time would be something incredible ; and if these records
were published annually, the public interest would be kept
alive, and the endeavours of the Government would be
assisted.
If, in connection with this investigation, steps were taken
to mark in some permanent way the exact spots, whether
at houses or on the open ground, where thunderbolt explo-
sions had happened, probably much advantage would
ensue ; and especially would this course seem appropriate
in cases where life had been lost. 1
We know from experience, and from the manner in which
explosions must necessarily be influenced by terraneous
circumstances, that there is good reason for believing that
where a thunderbolt has once occurred it is likely to occur
again. 2
Hence a mark of some kind would be not only valuable
as a memorial of the past, but also instructive as a guide
for the future ; and if the researches of the Government
should lead, as perhaps they might, to some kind of electro-
geographical or electro-geological survey 3 of a district
being commenced, these marks would probably be of much
assistance.
Again, a great deal of scientific information might pro-
bably be amassed through the agency of the Government, in
connection with the proposed investigation, not only on
the subject of thunderstorms, but also on that of all terres-
trial phenomena more or less associated with electrical
1 III. 10. 2 VII. C 11. 3 VII. Ay.
PRACTICAL MEASURES ADVOCATED. 269
IX. A I.
action, viz. earth currents, aurorse, magnetic storms, earth-
quakes, volcanic eruptions, and waterspouts. 1
At the present time there appears to be no organization
in the United Kingdom for obtaining and recording accu-
rate information regarding accidents by lightning ; and for
whatever knowledge we obtain of them we appear to be
mainly indebted to the pens of the gentlemen whose
business it is to supply the local press with news of
abnormal events, 2 for the metropolitan press does not
seem to be able to devote much space to the publication of
intelligence regarding the ravages of lightning. 3
Under any circumstances the knowledge afforded by the
press is but slight, and the death of an agricultural labourer
by lightning elicits less publicity than would be the case
if he had died from hydrophobia, or had been killed in
a railway accident, or had been driven over in the streets ;
yet it is clear that in each instance of death by lightning
immense benefit would be derived from a publication of
the details of the scene of the occurrence, of the clothes
and metals on the person of the deceased, of the traces
left by the thunderbolt, and of the proceedings at the
coroner's inquest. 4
Of course the reason for the scanty information ob-
tainable on this subject through the usual channels can
be none other than the want of public interest in the
matter ; and if any measures on a comprehensive scale
are to be adopted in this country with a view to the
prevention of loss of life by lightning, it seems essential
that the initiative should be taken by Government.
(b) The Defence of Towm.
The defence of towns from thunderbolts might doubt-
less be dealt with by the municipal authorities.
We have already suggested that underground metal
pipes (e.g. gas and water mains) and pavements are
1 I. 73. 2 III. 137, 141, 146, 148, 149, 152, 173, 183190.
3 III. 151. - * I.-D 65.
270 LIGHTNING.
IX. B.
probably elements of efficacy in preventing or diminish-
ing thunderbolts. 1
If these views, then, be sound, it would be a matter
of consideration for the smaller towns, as yet unprovided
with such advantages, to hasten the time for supplying
themselves therewith.
Towns appear to have as a rule so much immunity
from injury by lightning as compared with villages and
the open country, 2 that probably no other protective
measures than those above mentioned would be needed
by them apart from the special defence of particular
buildings containing prominent elevations.
(B.) THE DEFENCE OF CONSTRUCTIONS.
Pending the gathering of more detailed and more
scientific information regarding the action of lightning
than we at present possess, the following suggestions
are offered regarding the defence of constructions.
There appear to be two broad principles which may
be taken as the basis of means intended to secure build-
ings from thunderbolt explosions, viz. :
(1.) Insulation.
(2.) Leakage.
The insulating principle can be carried out by two
distinct measures, viz. :
(a) The removal of metals and explosive con-
ditions from the outer walls.
(5) The reduction of the explosive conditions
of the surface of the ground immediately around
the building.
The leakage principle can also be carried out by two
separate measures, viz. :
(0) The conversion of chimney grates into electric
taps.
1 VII. G d. 2 I. G 35, 36.
PRACTICAL MEASURES ADVOCATED. 271
IX. B a.
(d) The application of electric taps to the ground
surrounding the building.
We have thus four protective arrangements, any of
which, according to circumstances, can be used for the
defence of buildings.
(a) The Removal of Metals and Explosive Conditions
from the Building.
If the views that have been laid before the reader on
the subject of the danger arising from the presence of
metals on the roofs and outer walls of buildings, and
especially on their exterior surfaces, be correct, 1 it is
manifest that in designing a building, the defence of
which from thunderbolts happens to be an important con-
sideration, care should be taken to avoid altogether the
use of this material externally in positions elevated above
the ground, and, as far as possible, internally, in contact
with the roof and outer walls.
We consider that this absence of elevated metal from the
outer walls is, with all buildings in special need of pro-
tection, a vital necessity ; for (independently of theory) all
experience points with unswerving finger to the law that
exposed elevated metal is, as regards the action of light-
ning, a source of danger. 2
We will now consider briefly some of the practical archi-
tectural arrangements which might be conveniently enter-
tained at various kinds of buildings with a view to the
avoidance of metal.
In the first place there are the factories, laboratories, and.
magazines of gunpowder and other combustibles ; 3 these
may be considered the forms of building which above all
others require defence from thunderbolts.
In the design and construction of these buildings, there
seems no reason why their exterior surfaces should afford
i VII. Bd,/,?, t. 2 C3. * VII. C 1,0.
272 LIGHTNING.
IX. B a.
the slightest appearance of metal ; and, internally, the
locks, bolts, and hinges of the doors and shutters would
appear to be all that is necessary ; for although the heavy
vaulted roofs appropriate to powder magazines l are un-
desirable in factories and laboratories, yet very light
Portland cement concrete flat arches (which are practically
beams) might easily be adopted for these latter buildings.
As regards other kinds of buildings needing special pro-
tection from lightning, the following arrangements are
viz. :
(1.) The material of the walls would be brick,
stone, concrete, or other slowly collecting material,
but not metal or wood.
(2.) All metal work on the outside of the building,
except close to the ground, would be rigidly
omitted, e.g. weathercocks, spindles, finials, vanes,
balls, crosses, chimney-pots, roof coverings, ridge
crestings, eaves gutters, rain-water pipes and
balconies.
(3.) Wooden roof coverings would be avoided, and
the use of woodwork on the exterior of the walls
would be as sparingly adopted as practicable. 2
(4.) If ordinary pitched roofs be used, the covering
would be of tiles in lieu of slates, 3 whereby the
copper nails necessary for fixing the latter, and
also the leaden flashings, ridge, hip, and valley
pieces, frequently accompanying their use, would
not be required ; and the roof framing would be
of wood, not of iron.
(5.) Flat asphalted concrete fireproof roofs would
(notwithstanding the iron girders buried in and
supporting them) probably be fairly secure.
(6.) Chimney-pots would be of earthenware or terra
cotta.
(7.) The terminations of church spires, pinnacles,
i IV. 19. 2 VII. C 6. 3 I. D 49.
PRACTICAL MEASURES ADVOCATED. 273
IX. B a.
gables, &c., would consist of crosses, bosses, or
other ornaments, made of stone or terra cotta.
(8.) Eaves gutters and rain-water pipes would be
formed of stone, concrete, earthenware, terra
cotta, or kindred materials, but never of metal or
wood.
(9.) In the construction of all outer walls, the use
of tie rods, hoop-iron bond, lead joints, gratings,
and metal work generally, would be avoided as
far as practicable ; in block stonework in spires,
towers, and elevated features, slate dowels would
supplant iron ones, and the use of metal cramps
would be avoided.
(10.) Clocks would not be set high up in church
towers, turrets, campaniles, or other elevated
features of buildings.
(11.) Bells would also not be set high up in church
towers or campaniles.
(12.) Iron floors, columns, and staircases in the
interior of the building would be avoided.
(13.) No masses of metal, e.g. safes, organs, and
large mirrors, would be placed inside the building
in contact with the outer walls; and smaller
metal surfaces, e.g. gas and water pipes, would
also be kept, so far as practicable, away from
these walls.
(14.) Stained windows of churches 1 would not be
covered with wire guards ; probably stout glass
shields could be employed as substitutes.
Probably other means would also occur to architects
whereby the use of metal in and about the building might
be diminished.
The foregoing proposals are not made with reference
to all buildings, but only as regards those which in the
opinion of the architect, owner, or occupier, demand special
1 III. ill, 172.
N 3
274 LIGHTNING.
IX. B 0.
protection from lightning, whatever may be the cause
assigned.
It is submitted that this category should generally in-
clude the following, viz. all buildings connected with
the manufacture, manipulation, or storage of powder or
other combustibles ; tall chimney-shafts ; monuments and
works of art ; churches, and other buildings, whether in
town or country, having elevated features, e.g. spires, pin-
nacled towers, domes, cupolas, turrets, and belfries ; large
stores, warehouses, and factories, in exposed positions ;
and country labourers' cottages.
These buildings would all be dealt with according to
their respective circumstances so as to reduce the amount
of metal about them to a practicable minimum.
The chimney-stalks of furnaces are, owing to their great
height, and to the f acilitative lining of their interiors, pecu-
liarly liable to be struck by explosions ; hence every pre-
caution should be taken, in their construction, as regards
metals. 1
The custom of erecting stone columns of considerable
height to support statues and other metal works of art 2
appears to have died out in this country ; but, independently
of the danger from being struck by lightning, it seems to
be somewhat inappropriate to place statues of eminent men
on pedestals so high that their features cannot be dis-
tinguished, besides being a very expensive course to adopt.
The vanes and weathercocks of gilt copper or other
metal, which almost invariably surmount the spires and
pinnacles of churches, seem to be specially useless and
dangerous ornaments. 3
When untarnished, the gilding has not an unpleasing
effect to the eye, but it is hardly doubtful that delicately-
carved Latin or Greek crosses or other stone ornaments
would have an equally good appearance, and would be
more in harmony with good architecture.
1 III. 96. VII. B k. 2 III. 74.
5 III. 7, 51, 52, 62, 68, 131133, 188.
PRACTICAL MEASURES ADVOCATED. 275
IX. B a.
It is probable that metal ornaments on the summits of
church spires have many a disastrous explosion to account
for ; take for instance the case of St. Martin's Church on
the 28th July, 1842. 1 Here the vane was 8 feet long by
6 feet wide, and the vane spindle was 4 inches square in
section, and 27 feet long.
As regards church clocks and bells, 2 it is suggested that
both might conveniently be placed much nearer the ground
than is usually the case; that in many churches they
might without inconvenience be placed in some part of the
building other than the tower or most elevated feature ; 3
and that, in some instances, they might advantageously
be dispensed with altogether, as, in fact, in dissenting
churches in this country is always the case as regards bells,
and usually as regards clocks.
Large stores, warehouses, and factories, in exposed
positions would probably receive advantage from such of
the proposed measures regarding the removal of metal as
could be conveniently applied to them. 4
Labourers' cottages in the country, whether in villages,
or isolated, are specially in need of precautions regarding
metals ; 5 for they appear to be visited by thunderbolts
with a proportionally greater frequency than well-built
houses.
Whether castles, halls, and gentlemen's houses in the
country, 6 substantial farm-houses, 7 and farm buildings 8
should be treated in the manner proposed, or should be
specially dealt with at all qua defence from lightning,
would depend a good deal on the circumstances of the
locality, of the building, and of the occupier.
Some districts are seldom visited by thunderbolts ; 9 and
1 HI. 51. 2 In . 16, 36, 51, 52, 78, 79, 111, 128.
3 1. F 21 ; G 13. * III. 39, 86, HI, 189, 197.
* VII. C !>;.
III. 49, 55, 67, 79, 117, 121, 160, 177, 183, 186.
7 III. 184, 200, 201. 8 I. G 31. III. 113, 163, 202.
9 I. G 11, 26, 27, 30, 32.
276 LIGHTNING.
IX. B t>.
in these regions there would be less necessity for taking
special measures for the defence of private buildings.
The surroundings of the house, e.g. water, rock, trees,
adjacent buildings, the features of the country, the eleva-
tion, the degree of exposure, are, of course, all matters to
be taken into account. 1
Lastly, the occupier's pocket, and his or her views
generally concerning the importance of the dangers due to
thunderbolts, are important factors in the question. 2
It is considered that ordinary town houses, without
prominent features, in towns supplied with gas or water,
would not as a rule need special treatment for defence
from lightning, either as regards metals, or in any other
way. 3
(b) The Reduction of the Explosiveness of the Ground.
It would be advisable to build all constructions on tho-
roughly dry sites, and, wherever practicable, on rocky
ones. 4
Powder magazines should be constructed underground
whenever such a course is feasible.
All buildings, as to which it is an object that they should
be specially protected from lightning, should be kept well
away from the banks of small rivers and small sheets or
surfaces of water ; 5 and probably the sites of all new con-
structions of the kind we have proposed to take precautions
with as regards metal, would be worthy of special atten-
tion in regard to the nature of the soil and of the sur-
roundings.
These measures would, however, be hardly needed in
the cases of such buildings forming parts of the streets of
towns supplied with gas or water.
Having done, then, all we can, by natural means, to
diminish in the immediate vicinity of such buildings as we
1 VII. A, * III. 121. 3 VII. G rf.
< VII. A d, 5 VII. A b.
PRACTICAL MEASURES ADVOCATED. 277
IX. B b.
specially desire to protect from thunderbolts the conditions
tending to cause them, the question arises whether the
collectivity of the surface of the ground lying close to the
walls may not be advantageously reduced by artificial
means, viz. by paving. 1
The constructions to which, provided they contained no
metal on the exterior surfaces of their outer walls, the
measure of paving the ground immediately around those
walls might advantageously be applied, would probably
be all those proposed to be treated in regard to metal,
except labourers' cottages, where, in most cases, the expense
would probably be too great.
The pavement proposed is one of the following kinds,
or of a nature kindred thereto, viz. :
(1.) Squared stone flagging not less than 2 inches
thick, set in cement, and bedded on concrete.
(2.) Bricks, flat or on edge, set in cement, and
bedded on concrete.
(3.) Cement concrete.
(4.) Concrete coated with asphalte.
(5.) Tar pavement.
The total depth of masonry should in no case be less
than 6 inches ; the kerb should be at least 6 inches high
above the ground adjacent ; the width of the paving should
be from 3 to 6 feet, and there should be thoroughly good
contact between it and the wall of the building.
From a sanitary and a . convenient point of view, a
pavement around any building is always an advantage ;
and, qua lightning, the walls would certainly when thus
girt appear to run less chance of being utilised as a path-
way by an explosion from the adjacent ground.
The system would be especially applicable to buildings
of no great area, such as usually are magazines and
factories for explosives, and monuments or works of art ;
1 VII. A e.
278 LIGHTNING.
IX. B c.
for the expense of completely surrounding such construc-
tions with pavement would not be great.
At buildings containing elevated features, as, e.g.
furnaces with tall chimney-stalks, and churches with towers
or spires, the pavement would, where desirable, merely
surround the bases of such features, or would cover the
nearest ground thereto close to the walls, if such bases did
not reach the external ground. In the latter case, the
following would be a convenient rule for obtaining ap-
proximately the length of pavement required, viz. find
from the plan the girth which the base of the elevated
feature would approximately have, supposing its walls
or sides had everywhere reached the ground, perpen-
dicularly from where they are stopped ; and take this girth
as the length of the inside edge of the necessary paving.
We have already adverted to the fact of most buildings
in towns being enclosed by pavements. 1
(c) The Conversion of Chimney -grates into Electric Taps.
The best forms of lightning protective apparatus for
buildings now demand our attention.
In the country, the portions of houses that most cause
explosions and most suffer from them are generally the
chimneys. 2
We propose, therefore, to apply a special arrangement to
the fireplaces on the lowest floors of country houses and
cottages, whereby, if possible, these masses of metal, and
the sooty chimney flues leading from them, may have their
usual function of local dielectric converted into the much
less dangerous one of local plate, 3 and the grates or ranges
themselves may form portions of taps for the purpose of
ridding the ground adjacent to them of charge.
The proposed plan is merely to connect the grate by
means of one or more iron bars to the ground below, and
to fix on the grate a few short sharp iron spikes.
* VII. A e. 2 VII. B k. 3 II. E 7.
PRACTICAL MEASURES ADVOCATED. 279
IX. B e.
The connection might be in the form of a single piece of
iron of any convenient shape, riveted or otherwise fastened
to the bottom of the ironwork of the grate, or range, and
extending about 12 inches vertically into the natural soil
below the hearth ; but two or three of such connections
would be better than one.
The spikes might be quite small (say 2 inches long), and
might be fixed in any convenient parts of the grate, and
so as to point either upwards, downwards, or in any other
direction ; for their action would be the same in all cases,
and however placed they would certainly tend to eject at
all times any electricity which might collect in the ground
adjacent to the chimney.
The fact of these points being practically inside the
house would not affect their power. 1
The application of the above measure in its simplest
form to the grate of a labourer's cottage in the country
would be very inexpensive, and could easily be effected by
a village blacksmith.
For the defence of the chimneys of sitting-rooms on the
lowest floors of country houses it might perhaps be worth
while expressly to manufacture grates with wide vertical
horns projecting from their bottoms (to sink into the soil),
and numerous ornamental pointed projections on any
portion of them above ground.
The points of grates arranged as proposed could always
be kept sharp without difficulty ; and the hearth-stones
could be arranged so that (if required) parts of them could
be periodically lifted in order to examine the earth contact
of the connections.
It is submitted that, with the basement fireplaces treated
as proposed, labourers' cottages, and all ordinary houses
in the country, such as, e.g. country gentlemen's seats,
parsonages, and farm-houses, without prominently elevated
features or any great amount of elevated metal on their
1 V. B 20.
280 LIGHTNING.
IX. B d.
exterior surfaces, and not otherwise in need of specia
treatment, would be fairly well defended from thunder--
bolts.
The chimney-stalks of furnaces l would also doubtless be
rendered more secure if similar measures were adopted
with regard to any masses of metal connected with the
boilers or fireplaces lying near the bottom of the shaft.
(d) The Application of Electric Taps to the Ground surrounding
the Building.
The form of lightning protector which we advocate as a
substitute for the lightning rod in present use will now be
described.
"We have submitted that the advantages of the present
form of lightning rod are measured by the extent to which,
by means of its root and point, it taps the ground around
the building ; that as a rule the root is so arranged as to
tap a minimum portion of this important ground ; that
the stalk is an unmitigated disadvantage ; and that the
system when carried out in the complete manner advocated
by modern authorities is costly to erect, and liable to
several sources of failure after erection. 2
The principal conditions, then, that we propose to adopt
in the new form of apparatus are as follows, viz. :
(1.) The protector must be arranged so as to tap
the ground lying close around the building or
feature to be defended to the maximum extent.
(2.) It must have no stalk or exposed elevated
surface of metal.
(3.) It must be cheap to erect.
(4.) It must not be liable after erection to any
material source of failure.
Acting on these views, we suggest a form of lightning-
1 II. G 17. 2 VIII. B D.
PRACTICAL MEASURES ADVOCATED. 281
IX. B d.
protector for buildings which may not inaccurately be
termed an electric tap. 1
It consists, in its complete form, of a plate of iron laid in
the ground a few inches below the surface surrounding
the building, close either to the walls or to the kerb of any
pavement, of the nature and dimensions proposed,
adjoining them, and presenting slightly above the surface
of the ground numerous sharp iron points.
Old metal of any kind or shape would do for the plate,
and any sort of metal spikes attached thereto, and appear-
ing above the ground just so high that the points could be
conveniently kept sharp and free from injury, could act as
points ; but, in order to assist the ideas, it may be useful
to suggest a definite form and dimensions, which, under
ordinary circumstances, would be efficient, convenient, and
inexpensive.
The following specification is therefore submitted for
the construction and fixing of these taps, viz. Wrought-
iron plates, 4 feet long, 6 inches wide, and ^ inch thick,
laid flat in the ground with the edge on one side touching
the wall, or vertically underneath the edge of the pave-
ment kerb, at a depth of 6 inches below the surface, and
placed end to end in contact with each other ; each plate to
have riveted in it two round wrought-iron vertical rods, each
| inch in diameter, 12 inches long, and sharply pointed at
the upper extremity ; the rods to be fixed at 2 feet distance
from each other, 1 foot from each end of the plate respec-
tively, and 1 inch from the edge of the plate's inner side ;
the soil excavated to be compactly refilled over the plates
to the original level, so as to allow of the upper 6 inches of
the rods to project above the surface of the ground; the
exposed portions of the rods to be painted or tarred.
The weight of such a plate made at Devonport was
20 Ibs., and the cost of it was 5s. 7^d. ; thus the expense
of the system, including all labour, may be put at Is. 6d.
per running foot.
1 VII. G c.
282 LIGHTNING.
IX. B d.
The plates can be prepared by any smith, and can be
laid by the occupier of the building without the interven-
tion of an electrician ; the points can always be seen and
be kept sharp ; there is practically no exposure of metal ;
the building is not disfigured; and whenever it is con-
sidered desirable to examine the plates, all that is needed
is to remove the small layer of superincumbent earth.
Cast-iron taps, with continuous vertical webs of an
ornamental pattern surmounted by a fretwork of points,
might be appropriately employed at certain kinds of
buildings, in lieu of the wrought-iron form above specified.
Such an apparatus as proposed would, according to our
views, exercise a beneficial tapping function in any kind of
ground that it was placed in, however rocky or dry the site
might be.
Wherever the metal should touch the rock, the electrical
contact between the plate and the earth would doubtless be
less complete than when a certain amount of moisture was
present; but in these rocky situations, according to the
theory advanced in Part II., there is proportionally less
possibility of a charge accumulating to any extent ; l and
if it should do so, the amount of electricity tapped by the
apparatus would be correspondingly increased ; in fact, the
power of the tap would vary with the explosive condition
of the ground; and the more the apparatus should be
needed, the more it would respond to the call.
That such a contrivance, or indeed any that can be
devised, can be relied on absolutely to prevent explosion,
seems quite out of the question ; but, so far as we are
aware, it certainly is not liable, qua the object for which
it is intended, to any source of failure.
Although, in its complete form, the proposed electric
tap would surround the whole building, still it is con-
sidered that this course would only be needed with
buildings like powder magazines, which require extra-
i VII. A d.
PRACTICAL MEASURES ADVOCATED. 283
IX. B d.
ordinary precautions, though it might conveniently be
applied also to others which only occupied a compara-
tively small area, such, e.g. as monuments.
When applied, then, to buildings in general, the tap
would usually merely embrace either the base of any
prominently elevated feature needing special protection
e.g. the spire or tower of a church, the chimney-stalk
of a furnace or the pavement enclosing that base, and
where such feature did not reach the ground on all sides,
the length of tap to be used might be approximately regu-
lated by the same rule as that already suggested for the
length of the inside girth of the pavement proposed to be
laid adjacent to the feature's imaginary base, and the tap
would be disposed over the length or lengths of ground
lying close to the walls or pavement kerbs nearest to such
imaginary base ; but the exact arrangement of the tap
would of course depend on the circumstances of the
building.
It might occasionally be considered sufficient if only the
salient angles of the base or imaginary base of an elevated
feature were each guarded by a short length of tap.
Where any particularly elevated features were wanting,
those most prominent laterally, e.g. the corners or pro-
jecting portions, might be protected.
In cases where the building is enclosed with pavement
as proposed, it is considered that the efficacy of the
apparatus in tapping the electricity at the base of the
walls would not generally be affected by the short
distance the tap would be kept therefrom, necessitated by
the width of the pavement ; but should the nature of the
ground lead to the idea that this might possibly be the
case, the pavement would have to be omitted.
The following constructions would, as a rule, be supplied
with electric taps, viz. :
(1.) Buildings for manufacturing, manipulating,
or storing gunpowder or other explosives.
These would be the only kind of buildings that
284 LIGHTNING.
IX. B d.
(it is proposed) should, of necessity, be completely
surrounded by the taps.
At the rate of Is. 6d. per lineal foot, the cost of
defending an existing magazine holding 10,000
barrels of powder (500 tons), the girth of the
pavement around which is 474 feet, would be
35/11.
The actual cost of defending a similar magazine,
holding only 2,000 barrels, on the system now in
force, has been found to be 112/2/11.
(2.) Tall chimney-stalks of furnaces.
To be dealt with qua the stalks only.
(3.) Monuments, columns, and works of art.
To be surrounded when of small area.
(4.) Churches and other buildings with prominently
elevated features.
To be dealt with qua the elevated features only.
(5.) Large stores, warehouses, and factories, in
exposed positions.
These would generally not present any elevated
features, and the prominent corners should in
such cases be protected for a short distance on
each side of the angle, and especially those most
exposed to the winds usually accompanying the
thunderstorms of the locality.
Ordinary country houses, and country labourers' cottages
are not intended, as a rule, to be provided with these taps.
In the case of country houses, however, it would
probably, as we have already stated in re metals, be a
question dependent on circumstances whether such special
protection would be desirable or not ; and since the expense
of the proposed taps would be small, doubtless it might
sometimes be worth while to employ them at such houses,
and especially in cases where the removal of external
elevated metal should cause no inconvenience.
PRACTICAL MEASURES ADVOCATED. 285
IX. B 9.
We have mentioned the manner in which we consider
that the ground around the houses of large towns is
already tapped by means of their gas and water pipes ;
and of course houses in the country supplied with either
of these services would be to a great extent in a similar
condition.
(e) Summary of Proposals for the Defence of Buildings.
The following is a summary of the arrangements recom-
mended for the defence of buildings of various kinds from
the effects of lightning ; but, provided that pavement was
never employed without the removal of external metal, it
would generally depend on the circumstances of the par-
ticular building whether all of the proposed measures
would be needed, or whether the adoption of some one or
more of them would be sufficient.
(1.) Buildings connected with Gunpowder or Explosives.
(a) Choose a rocky or dry site, remote from the
banks of rivers and small sheets of water, and as
little exposed as possible. When practicable and
convenient, select an underground site for a
magazine.
(ft] Avoid elevated features in the building, and
keep it as low as possible.
(y) Omit all metal on its external surface, in the
body of the walls, and adjacent to the outer walls
inside the building.
(8) Pave the strip of ground immediately around
the building.
(e) Lay an electric tap in the ground around the
building.
(2.) Chimney Stalks of Furnaces.
(a) Omit all metal on the external surface, and, so
far as practicable, in the body of the walls and
inside the shaft.
286 LIGHTNING.
IX. B e.
(ft) Pave the ground adjacent to the base of the
stalk.
(y) Convert the metal work of the furnace into an
electric tap.
(8) Lay an electric tap in the ground adjacent to
the base of the stalk.
(3.) Monuments, Columns, and Works of Art.
(a) Avoid surmounting with metal in the form of a
statue, trophy, or other work of art ; and omit all
metal on the external surface.
(ft) Pave the ground all around the pedestal of the
work.
(y) Lay an electric tap in the ground around the
work.
(4.) Churches and other Buildings, with Prominently Elevated
Features, not included in (2) or (3.)
(a) Omit all metals as in (1) at the elevated features,
and all external elevated metals at the rest of the
building.
(ft) Pave the ground all round the building, or
adjacent to the bases of the elevated features,
(y) Lay electric taps in the ground adjacent to the
bases of the elevated features.
(5.) Large Stores, Warehouses, and Factories, in Exposed
Positions, not included in (4.)
(a) Keep the amount of external elevated metal at
a minimum.
(ft) Pave the ground all around the building or
adjacent to the prominent angles,
(y) Lay electric taps in the ground adjacent to the
prominent angles.
(6.) Country Labourers' 1 Cottages,
(a) Omit all external elevated metals.
(ft) Arrange the grates on the lowest floors as
electric taps.
PRACTICAL MEASURES ADVOCATED. 287
IX. B/.
(7.) Country Houses, not included in (4) or (5), and not other-
wise considered to need special protection.
(a) Omit external elevated metals so far as con-
venient.
(/?) Arrange the grates on the lowest floors as
electric taps.
(8.) Farm Buildings.
Omit external elevated metals so far as convenient.
(9.) Town Houses where gas or water is laid on, not included
in (4) or (5.)
Nil.
(/) The Defence of Coal Mines.
The dangers possibly due to the deep shafts of mines
have been already alluded to ; * and it seems quite possible
that the recent terrible accident at the Bisca Colliery during
a severe thunderstorm may have been caused by an accu-
mulation of thunderbolt explosive conditions at the bottom
of the shaft, and by the absence of restraint caused by the
sides of the shaft. 2
It is suggested that coal mines should always be treated,
qua lightning, as stores of " fire-damp," and should, in
like manner as stores of other explosive substances, such,
e.g. as gunpowder, be defended by all known means from
being ignited by lightning.
Coal mines would seem in fact to be far more in need of
such protection than powder magazines; for the former
generally contain at all times of the day and night a great
number of human beings, whilst the latter seldom contain
any, and never when a thunderstorm is known to be in
progress.
In dealing with mines, we are as yet without actual
experience ; for there is apparently no case on record of a
1 VII. B/.
2 It appears from the Report of the Lightning Rod Conference that
on the 12th July, 1880, lightning actually entered the workings of
Tanfield Moor Colliery.
288 LIGHTNING.
IX. B y.
mine positively known to have been exploded by a thunder-
bolt ; still, every reasonable precaution would probably be
worth adoption ; and if the theory of the proposed electric
taps be sound, much benefit might arise from the use of
them at the bottom of deep shafts.
It seems quite possible that the coal at the foot of the
shaft may be able to collect electricity with some rapidity ;
for carbonaceous substances appear to rank after metals in
their influence as collectors ; and if we once allow that
lightning ascends from the earth instead of descending on
it from the clouds, 1 there is good reason for presuming
that mines may occasionally be the scenes of thunder-
bolts.
(g) The Defence of Ships.
We do not propose to make any detailed suggestions
regarding the defence of ships, and for the following
reasons, viz. :
(1.) Iron ships, whether carrying lightning rods or
not, are apparently never struck by thunderbolts. 2
(2.) The form of lightning rod in use in H.M. ships
appears to have been (though not without ex-
ceptions) 3 successful in tapping any electricity
that may have accumulated around them. 4
(3.) To judge from "Lloyd's List," lightning acci-
dents at sea seem, at the present time, to be rare ; 5
nevertheless, it appears that the larger wooden
merchant ships seldom carry lightning rods, and
the smaller ones never ; hence the inference is
that, in these days, thunderbolts do not often
occur at sea, and certainly not so frequently as
formerly. 6
It is submitted, however, that the principle of electric
taps, as proposed for buildings, could readily and ad-
i VI. B b. 2 VII. B d. 3 III. 69, 70, 99102.
* VIII. B. s III. 125. I. G 1-4.
PRACTICAL MEASURES ADVOCATED. 289
IX. B#; Co.
vantageously be applied to all kinds of ships ; for all that
they need for this purpose is the application of short points
at convenient places inside the hull in connection with the
iron or coppered bottom; and this would permit of the
dangerous and costly copper bands and tubes, fixed to the
masts and shrouds, in the present system of ships' lightning
rods, 1 being dispensed with.
(C.) THE DEFENCE OF INDIVIDUALS.
(a} Rules for the Guidance of Individuals.
As regards the defence of individuals from thunderbolts,
much good would probably result from the knowledge, and
carrying out, of a few simple rules.
It is submitted that one of the forms of Government
supervision might, in rural districts, advantageously consist
in circulating printed directions on the subject of defence
from lightning.
Pending the obtaining of further experience, the fol-
lowing suggestions are now offered for the guidance of
individual action during the progress of thunderstorms :
Inside Houses?
(1.) Whenever not inconvenient, vacate kitchens
and all rooms on the lowest floor where there are
fireplaces.
(2.) Where this is impracticable or inconvenient,
carefully avoid the neighbourhood of such fire-
places.
(3.) In all rooms, keep, as a rule, clear of the fire-
places and of the outer walls; and remain as
much as possible in the middle of the room.
(4.) Especially avoid the vicinity of any metals on
or near the outer walls, such, e.g. as balconies,
rain-water pipes, window bars, iron shutters and
doors, gas-pipes, water-pipes, tie rods, bell wires,
1 III. 69. IV. 44. 2 I. F 17.
290 LIGHTNING.
IX. a.
speaking tubes, safes, cisterns, sinks, large mir-
rors, gildings, and bedsteads.
(5.) Keep all windows, doors, and other openings
closed.
(6.) An underground vault or cellar is usually a
secure place. 1
(7.) Always keep chimney flues, and especially the
kitchen flue, fairly clear of soot. 3
In the Open Air.
(1.) If you be about to walk, ride, or drive, in
the country, during the summer or autumn in
thunderous weather, do not carry more metal in
any form about your person than is absolutely
necessary. 3
(2.) Under the above circumstances, when walking,
take an umbrella with you with as little metal on
it as practicable, and not a walking stick. 4
(3.) If overtaken by a thunderstorm get as soon as
possible inside any masonry building that may be
near, 5 or failing a house of this kind, the nearest
house of any sort ; but avoid wooden sheds and
out-buildings. 6
(4.) If there be no houses near, do not attempt to
obtain shelter anywhere ; but choose the ground
near you that appears to be naturally the least
exposed and the driest, and that is not close to
water of any kind, and sit or recline there covered
by your umbrella. 7
(5.) Avoid especially the neighbourhood of trees, 8
hedges, fences, walls, 9 steep faces of rock, and
all similar shelters. 10
i i. F i_3. 2 vn. B k. 3 I. F 15. VII. B e.
* VII. C 8, 9, K. III. 10. 5 II. E 22.
e VII. Brf,/; 08, p. 7 I. F13, U.
VII. C 5. 9 III. 20. 10 I. F 10.
PRACTICAL MEASURES ADVOCATED. 291
IX. C b.
(6.) If overtaken when riding, dismount ; l and, if
practicable, leave or secure the horse standing on
a site similar to that mentioned in (4), and sit or
recline in another similar position yourself, some
little distance away.
(7.) If overtaken when driving, 2 stop, and if in a
covered carriage, dismount from the outside, and
either get inside or take up a position, as in (4),
at some distance from it. If the conveyance be
uncovered, all should dismount and dispose them-
selves as in (4), at some distance off.
Some authorities have recommended the portions of
ground near, but not close to, shelters, such as trees, as
being safe positions, in comparison to other places, on the
principle that the shelter itself would as a rule be struck
by any thunderbolt that might occur thereabouts, and
thus the ground near the shelter, but not immediately con-
tiguous, would probably be rendered comparatively safe. 3
We must, however, remember that this neighbourhood
and especially if a human being were in it would, if a
thunderbolt struck the shelter, generally be the scene of a
return stroke ; and therefore, though life might be secure
there, still it would probably be at the cost of a more or
less severe shock ; moreover, it would be impossible to
estimate accurately the distance from the tree or shelter at
which immunity from a thunderbolt striking the tree might
end, and danger from other thunderbolts might begin.
(i) Agricultural Labourers.
The persons who appear to be most exposed to the effects
of thunderbolts are agricultural labourers. 4
They are frequently working in the fields when a
thunderstorm comes on, and they naturally seek refuge at
i VII. B e; 8, n . 2 VII. B e; C 8, r,. I. F 11, 12.
* I. F 9; G 8, 9, 1921, 36. VII. C 8, d, i, v.
o 2
292 LIGHTNING.
IX. C b.
the nearest shelter ; but this shelter is generally a tree or
slight wooden shed, and, so far from affording them pro-
tection from lightning, is constantly the cause of their
deaths by it. 1
The remedy that we propose is the substitution of
masonry for wood as the material for the construction of
field sheds, and the use of these sheds in greater numbers.
The labourers should be careful to leave their tools
where they have been working.
* I. F 10. VII. C 8, X, in.
INDEX.
ABEL, Professor, 34, 71
Acceleration, 3, 148
Accidental dielectrics, 201, 220,260
Adair, Mr., 93
Afghanistan, 44
Africa, South, 79, 113, 128
Agency, 145
Agram, 25
Aide - Memoire to the Military
Sciences, 12, 24, 25, 51, 73, 128
Air, 6, 7, 9, 10, 14, 28, 30, 61, 173,
189, 199, 204, 222, 290
Airth, Alexander, 124
Almshouses, 142
Amber, 47
America, North, 43, 45, 49, 58, 64,
73, 87, 89, 90, 93, 102, 103, 104,
107, 109, 110, 112, 115, 123
America, South, 45, 102, 108, 111
Ampere, M., 18
Analysis of incidents, 209, 258
Anderson, Joseph, 126
Anderson, Mr. K., 10, 13, 15, 16,
24, 29, 35, 36, 43, 44, 46, 48, 49,
50,51,52,57,58,64, 68,69,70,
73, 74, 75, 76, 82, 83, 84, 99,
102, 106,116,117,118,119,120,
121, 122, 123
Angularities, 152
Animals, 7, 9, 10, 31, 32, 39, 173,
192, 194, 218
Apennines, 45
Arago, Professor, 12, 13, 14, 15,
21, 23, 24, 25, 26, 27, 28, 29, 30,
31, 32,36, 37, 38, 39,43,44,45,
50, 52, 59,65, 72, 73,77,86,87,
88, 89, 90, 91, 92, 93, 94, 95, 99,
103, 104, 105, 107, 162, 223
Architects, 243, 273
Architectural arrangements, 257,
272
Architecture, works on, 74
Areas, large, 267
Articles of dress, 171, 172
Artillery, 38
Ashes, 7, 67, 68, 172
Asphalte, 71, 183, 184, 272, 276
Asphyxia, 33
Associated dielectrics, 220
Atlantic Ocean, 22, 86, 103, 108
Atmosphere, 7, 8, 11, 14, 15, 20,
46, 63, 80, 83, 154, 220, 231
Attraction, 1, 5, 6, 13, 35, 47, 80,
83, 146, 166, 199, 225, 226
Augustus, Emperor, 36, 37
Aurora, 16, 17, 18, 19, 20,21, 156,
159, 175, 232, 269
Austria, 43, 86, 92, 104
Aylesford, Lord, 87
pALCOMBE (a boy), 131
_D Balconies, 171, 272, 289
Balfour Stewart, Professor, 16,
19,20
Balloons, 12
Balls, 272
Balustrades, 171
Barns, 45, 73, 211
Batteries, coast, 71
294
IKDEX.
Beccaria, M., 50
Becquerel, M., 10, 52
Beds, 43, 217
Bedsteads, 172, 173, 290
Beer, 12, 228
Belfries, 200, 205, 274
Bellion, Mr., 90
Bells, 39, 43, 171, 205, 273, 275
Bell wires, 30, 289, 292
Beranger, M., 88
Berlin, 45
Bernouilli, John, 47
Be vis, Dr., 48
Bismuth, 9
Bituminous substances, 7, 173
Blomfield, Mr., Ill
Boats, 173
Boilers, 171
Bone, 173 .
Boyle, Eobert, 47
Bracini, M., 25
Brass, 56, 171, 213
Bricks, 82, 173, 184, 193, 194,
272, 276
British Association, 2, 265
Bronze, 171, 213
Brush discharge, 6, 64
Brussels, 54, 60, 65
Buchanan, Mr., 82
Bucharest, 25
Buffon, M., 48
Buildings, 30, 31, 35, 36, 70, 71,
72, 74, 77, 79, 80, 83, 84, 171,
172, 173, 174, 184, 199, 203,
210, 246, 262, 265, 271, 290
Buildings set on fire, 211
Bushes, 172
Butter, Mr. E., 123
Buys, Mr., 113
CAIRO, 45
Callaud, M., 65, 69, 73
Campaniles, 273
Canvas, 173
Caoutchouc, 10
Capacity, 2, 3, 145, 149, 150, 151,
153, 167, 185, 194, 199, 200
Carbonaceous suhstances, 172,288
Carriages, 173, 291
Carts, 173, 291
Cast-iron electric taps, 282
Castle, Mr., 112
Castles, 275
Cattle, 173
Causes of lightning rod failures,
259
Caves, 36, 203
Cavendish, Mr., 6, 49, 59, 92
Cellars, 290
Cement, 173, 276
Chalk, 7, 8, 9, 173
Chambers's Dictionary, 26
Chappe, Professor, 13, 27
Charcoal, 7, 8, 9, 10, 65, 69, 172,
252
Charcoal trenches, 187
Charge, 176
Chatham notes, 5
Chemical action, 2
Chili, 24, 25, 44, 160
Chimneys, 38, 44, 70, 71, 79, 206,
215, 278, 279, 290
Chimney-pots, 171, 200, 207, 272
Chimney-stalks, and shafts, 141,
142, 172, 200, 207, 208, 274,
278, 280, 284, 285
Chittenden, Mr., 131
Churches, 35, 50, 66, 84, 137, 138,
139,140,141,142,143,144,210,
272, 274, 278, 284, 286
Cisterns, 65, 67, 290
Clarke, Samuel, 126
Clay, 167, 173
Clerk, Maxwell, Professor, 83
Cliffs, 201
Clocks, 171, 205, 273, 275
Clothes, 171, 172, 197, 218
Clouds, 11, 12, 14, 15, 16, 27, 28,
29, 31, 46, 63, 80, 81, 154, 156,
157, 173, 176, 221, 223, 224, 225
Cloud explosions, 175, 223, 225,
228
Coalmines, 46, 201, 287
Coast, sea, 186
Coke, 7, 65, 66, 172, 252
Collecting plates, 147, 152, 156,
160, 191
Collection, 147
Collective substances, 179, 181
Collectors, 146, 150, 171, 172, 173,
288
Columns, 138, 171, 200, 258, 273,
274, 284, 286
INDEX.
295
Comazants, 22
Combustion, 11
Concrete, 71, 173, 272, 273, 276
Condensation, 5
Condenser, 5, 147, 150, 151, 152,
155
Condenser, terrestrial, 154, 170,
174, 203
Condensing plate, 147, 152, 191
Conduction, 48, 80, 147
Conductivity, 6, 9
Conductors, 4, 5, 9, 10, 146, 17 1,
172, 173
Conservatories, 173
Constructions, 188, 203, 211, 259,
270
Contact, 189, 190
Copper, 6, 7, 8, 9, 10, 52, 53, 54,
55, 56, 57, 58, 59, 63, 64, 68,
83, 171, 213, 249,250, 255, 272,
274
Corn, 43, 173
Cost, 51, 70, 74, 249, 250, 251,
252, 253, 265, 281, 284
Cottages, 207, 208, 211, 274, 275,
278, 279, 284, 286
Cotton, 8, 10, 173
Countries, defence of, 267
Country, 45
.Country houses, 208, 278, 279,
284, 287
Cows, 173
Cramps, 171, 273
Crosses, 171, 272, 274
Culley, Mr., 16, 68
Cupolas, 274
Current, 3, 18, 19, 20, 33, 49, 58,
146, 147, 149, 165
Cuvier, Professor, 24
D'ABBADIE, 13, 29
D'Alibard, 12, 48, 49, 241
Dam of reservoir, 152, 153
Dangers to interiors, 204, 206
Davy, Sir Humphrey, 10
Deaths, 31, 32, 33, 40, 41, 42, 43,
44, 292
Decomposition, 11,228
De Fcnvielle, M., 75
De la Rive, Professor, 20
De la Rue, Dr. Warren, 58
DeL'Isle,M., 13
Delia Torre, M., 25
Denmark, 120
Density of atmosphere, 231
De Romas, M., 50, 241
Deschanel, Professor, 3
Deviations of explosions, 261
Dielectrics, 5, 147, 152, 1G7, 191,
204, 220
Dillwyn, Mr k , 14
Distance, 148
Districts, defence of, 267
Districts, rural, 289
Discharge, electric, 6, 11, 59, 61,
83, 146, 148, 150, 151, 152, 153,
174, 175, 176, 177, 178
Diversities of opinion, 243
Doors, 173, 205, 289, 290
Dogs, 173
Donkeys, 173
Drainage, 84
Drain pipes, 70, 171
Driving, 198, 290
EARTH, 7, 9, 10, 14, 15, 16,
17, 19, 27, 28, 63, 80, 154,
156, 157, 177
Earth, "bad," 173, 259
Earth, dry, 66, 67, 68, 69, 173,
182, 189
Earth, "good," 173, 182
Earth, moist, 65, 66, 67, 68, 69,
81, 162, 173, 182
Earth connections, 56, 65, 66, 67,
68, 69, 70, 71, 75, 79
Earthquakes, 17, 23, 24, 25, 26,
44, 160, 269
Earth currents, 16, 17, 20, 159, 269
Earth's crust, 186
Earthenware, 173, 273
East India Company, 77
Eclair, 1', 176
Electricity, 1, 2, 3, 4, 5, 6, 16,
145, 146, 147, 148, 149, 150.,
151, 152, 153, 155
Electricity, atmospheric, 10, 20,
223
Electricity, negative, 4, 11, 15,
63, 145, 166
Electricity, positive, 4, 11, 63,
145, 166
296
INDEX.
Electricity, terrestrial, 10, 14, 21,
82, 156, 157, 179
Electricity, thermal, 2, 11, 18, 19
Electricity, voltaic, 1, 11
Electric connection, 188, 189
Electric fluid, 50, 62, 81
Electric machine, 47
Electric sparks, 6, 28, 47, 48, 166,
234, 241
Electric taps, 278, 279, 280, 281,
282, 283, 284, 285, 286, 287
Electricians, 69, 74
Electrified bodies, 1, 2, 4, 145
Electrolytic action, 65, 66, 190
Electro-motive force, 3, 146, 149
Elevated features, 274, -278, 283,
284, 285, 286
Elevated positions, 187, 274, 286
Elevation, 72, 185, 194, 200, 276
Encyclopaedia Britannica, 23, 24
Encyclopedia Metropolitana, 44
Energy, 1
Engines (railway), 172
England, 39, 40, 41, 42, 44, 55,
59, 69, 74, 76, 87, 90, 91, 92, 93,
94, 99. 100, 102, 103, 104, 106,
107, 108, 109, 110, 111, 113,
114, 115, 116, 117, 118, 119,
120, 121, 122, 123, 124, 126,
127, 128, 129, 130, 131, 132,
133, 137, 138, 139, 140, 141,
142, 143, 144, 173, 222, 240,
242, 243, 267, 269
Eruptions, volcanic, 17, 24, 25,
26, 156, 160, 269
Etna, Mount, 26
Evaporation, 11
Everett, Professor, 10
Explosion, 30, 146, 147, 150, 153,
165, 176, 177, 202, 208
Explosive action, 190, 191
Explosive conditions, 271, 276
Exposed positions, 187, 274, 286
TUCILITATION, 14 ?
_L Facilitators, 171, 172, 173
Facilitators, great, 171, 172
Facilitators, slight, 173, 191
Factories, 274, 275, 284, 286
Factories, gunpowder, 271, 274,
283, 285
Faraday, Professor, 61, 78
Farm-houses, 275, 279, 287
Fat, 8
Feathers, 7, 8, 9
Felt, 173
Fences, 171, 173, 190
Fields, 182
Finials, 171, 172
Fires, 38, 4 +
Fire balls, 229
Fire damp, 287
Fire-places, 38, 71, 279
Flagging, 277
Flagstaffs, 71, 162, 173, 194, 216
Flame, 7, 9, 63, 172, 207
Flammarion, M., 13, 20, 21
Floors, 38, 171, 173, 273
Fog, 44, 173
Foliage, 173
Force, 1, 3, 148
Force, expansive, 30, 31, 191
Formulae, electric, 148
Foudre, la, 176
France, 24, 26, 38, 39, 43, 45, 50,
57, 58, 59, 64, 74, 76, 86, 87,
88, 90, 91, 92, 94, 98, 123, 126,
176, 222, 242
Francisque Michel, M., 56, 62,
68, 76.
Franklin, Benjamin, 5, 12, 30, 37,
38, 48, 49, 56, 59, 60, 63, 69,
70, 74, 78, 92, 102, 238, 240,
241, 242, 248
Eraser, Lieut. T., 26
Friction, 11, 12
Fulgurites, 30
Fur, 7, 9, 173
Furnaces, 172, 208, 274, 280, 284,
285
Fusion, 30, 192, 260
r\ ALTON, Capt. Douglas, 71
Ij Galvanometers, 75, 255
Galvani, Professor, 31
Galvanic action, 255
Ganot, Professor, 1, 5, 6, 9, 10,
13, 16, 17, 18, 21, 22, 23, 27,
32, 37, 56, 57
Gaps, air, 50, 166, 241
Gas, 7, 8, 9, 10
Gasholders, 206
INDEX.
297
Gas-pipes, 66, 67, 73, 171, 205,
235, 251, 253, 270, 273, 276,
285, 287, 289
Gas works, 142
Gates, 171
Gavarret, Professor, 60
Gay-Lussac, Professor, 51, 173
Geography, 39, 42, 43, 44, 45
Geological formation, 185, 186
Germany, 59, 76, 90, 105, 116,
119, 120
Gilbert, Dr., 17, 47
Gildings, 38, 62, 213, 290
Girders, iron, 171
Glass, 6, 7, 8, 9, 10, 30, 38, 47,
60, 173, 200, 273
Gold, 9, 10, 171
Gordon, Mr., 1, 5, 10, 17, 19, 64
Government, 267, 268, 269, 289
Graphic newspaper, 23, 46
Graphite, 7, 9, 10, 172
Grass, 173, 233
Grates, 70, 171, 207, 278, 286,
287
Gratings, 273
Graves, Mr., 28, 85, 115
Gravity, force of, 225, 226
Gray, Mr. Stephen, 48
Griswold, Mr., 23
Ground, 11, 14, 15, 179, 185, 187,
190, 281
Guillemin, M., 82
Gunpowder, 72, 91, 105, 117,
128
Gutta-percha, 6, 7, 10
Gutters, eaves, 73, 171, 172, 173,
200, 272, 273
HAIL, 12, 13, 84, 172, 221
Hair, 7,8, 9, 173
Halley, Professor, 19
Hamilton, Sir Win., 25
Halls, 275
Hare, Professor, 65
Harris, Sir Wm. Snow, 1, 6, 7,
13, 15, 22, 35, 39, 51, 52, 53,
55, 60, 72, 77, 78, 79, 86, 88,
89, 92, 94, 95, 97, 98, 99, 100,
101, 102, 103, 104, 105, 107,
108, 109, 110, 162, 244, 249
Hartley, Mr. Thomas, 92
Hawksbee, Mr. 47
Hay, 173
Heat, 2, 16, 23, 191, 192
Heathcote, Mr. K. B., 46
Hedges, 173, 290
Hemp, 173
Henley, Mr., 6, 37
Herschel, Sir John, 11, 12, 13,
29, 30, 50
Hills, 185
Historical notes, 47, 238
Holtz, Professor, 36
Horses, 173
Houses, 173
Howorth, Mr., 24
Human bodies, 173, 192, 193, 194,
196, 202, 216, 217, 218,229
Humboldt, Herr Von, 18
Huts, 173
Hydraulic simile, 152
JOE, 7, 8, 9, 10, 13, 84, 172,
183
Iceland, 44
Illustrated London News, 111
Incidents, lightning, 86
India, 44, 103, 109, 113
Indian Ocean, 101
India-rubber, 6, 8
Individuals, defence of, 289
Induction, 1, 4, 5, 32, 33, 79, 147,
155
Inductive capacity, 5, 150
Influence, 147, 170, 171, 172,
173
Insulation, 4, 14, 48, 147, 270
Insulators, 4, 8, 9, 73, 74,81, 146,
150, 151, 173, 189, 244, 257
Interiors of buildings, 203, 204,
212, 273, 289
Ireland, 41, 109, 115, 128, 129
Iron, 6, 9, 10, 17, 35, 45, 49, 54,
65, 56, 57, 58, 59, 64, 65, 68,
70, 71, 82, 171, 172, 213, 214,
272, 273, 279, 288
Iron-pointed plates, 281
Iron ships, 288
Iron spikes, 278, 279
Italy, 45, 50, 87, 89, 91, 93, 95,
99, 104, 105, 110, 119, 122
Ivory, 173
298
INDEX.
JAMAICA, 44, 123
tl James, William, 124
Jenkin, Professor F., 2, 3> 4, 5,
6, 7, 15, 16, 19, 28, 31, 64
Joists, iron, 171
KAEMTZ, Professor, 11, 12, 13,
27, 43, 81
Ksempfer, M., 36
Kentish paper, 107, 129, 130,
131, 132
Kitchens, 207, 289
Kites, 50, 240
Kleist, Herr, 48
Kriel, Professor, 24
T ABORATORTES, gunpowder,
Lt 271,273,285
Labourers, 40, 41, 274, 275, 291
Lakes, 182, 187
Lambert, M., 13
Latimer Clark, Mr., 8, 29, 55,
71, 85, 115
Law, electric, 149, 165
Lead, 6, 9, 10, 70, 71, 73, 172,
213, 272, 273
Leaks, 4, 146, 148, 151, 153, 176,
194, 270
Leaks, atmospheric porous, 231,
232
Leaks, terrestrial, 175, 231, 232,
233, 234, 235, 236, 237
Leather, 7, 8, 9, 173, 197
Le Gentil, M., 13
Lenz, Herr, 10
LeRoy, M., 116
Leydenjar, 5, 48
Lieberklihn, Dr., 48
Lighthouses, 60, 211
Lightning, action of, 30, 86
Lightning, ascending, 27, 28,
161, 264
Lightning, ball (globular), 26, 29,
229
Lightning conductors, 36, 63, 80,
81, 82, 83, 85, 242
Lightning, definition of, 26, 28
Lightning, descending, 27, 28,
160, 169, 242
Lightning discharge, 15, 25, 26,
27, 28, 29, 46, 47, 48, 174, 176
Lightning engineering, 47
Lightning flashes, 11, 12, 26, 29,
49,50
Lightning, heat, 28, 156, 175,
232
Lightning incidents, 86, 209
Lightning, mechanical force of,
163, 164, 168, 193, 219
Lightning protectors, 34, 230
Lightning, sheet, 26, 28, 156, 175,
232
Lightning, zigzag, 26, 29, 191
Lightning rods, 48, 49, 50, 53,
73, 171, 202, 238, 288
Lightning rods, action of, 239,
245, 261
Lightning rods, application of,
70, 71, 72, 73, 74
Lightning Rod Conference, 85,
265, 287
Lightning rods, cost of, 249, 250,
251, 252, 253, 265, 284
Lightning rod details, 51, 52, 53,
54, 55, 56, 57, 58, 76, 137, 244,
254
Lightning rods, disadvantages of,
246, 280
Lightning rods, disfiguring ten-
dencies of, 257
Lightning rods, fused ends of,
260
Lightning rods, history of, 47,
238
Lightninar rod incidents, 258,
261, 262, 263
Lightning rod inspections, 75, 76,
255, 256, 257
Lightning rods, instances of, 137
Lightning rods, mechanical in-
juries to, 260
Lightning rod points, 54, 59, 60,
61, 62, 63, 64, 75, 79, 238, 250,
251, 253, 256, 257, 264, 265
Lightning rods, protective power
of, 51, 77,78,79, 80,81,82,83,
84, 85
Lightning rods, roots of, 238, 245,
246, 247, 251, 252, 256, 264,
265
Lightning rods, stalks of, 238,
INDEX,
299
244, 247, 248, 251, 254, 255,
264, 265
Lightning rods, sources of failure
of, 264
Lightning rods struck, 50, 51, 77,
78, 163, 164, 169, 193, 243, 258
Lightning strokes, 32, 78
Lightning strokes, accurately de-
fined, 219, 230
Lightning strokes, divided, 29
Lightning strokes, horizontal,
219
Lightning strokes, repeated, 219
Lightning strokes, simultaneous,
208, 218
Lime, 7, 9, 10, 173
Limestone, 14, 173
Linen, 8, 10, 173
Lloyd's List, 288
Local dielectrics, 189, 192, 193,
198, 207, 208, 220, 260
Local plates, 188, 191, 192, 194,
196, 219, 260
London, 42, 45, 50, 95, 97, 101,
105, 106, 108, 116, 120, 121,
122, 124, 125, 126, 131, 141
Ludolf, Herr, 48
Lunn, Mr., 8, 27
MACTAGGART, Mr., 82
Maflei, Professor, 27
Magazines, gunpowder, 51, 55, 69,
71, 72, 82, 139, 211, 271, 274,
276, 283, 284, 285
Magnetic storms, 16, 17, 18, 19,
20, 24, 158, 269
Magnetism, 10, 17, 30, 158
Magnetism, the earth's, 16, 17,
18, 19, 21, 157
Mahon, Lord, 31, 50, 162
Majendie, Major (report of), 117
Malaise, 24, 228
Malta, 127
Manilla, 25, 26
Mann, Dr., 13, 14, 29, 32, 35, 37,
43,53,54, 60, 61, 65, 66, 73, 75,
79, 113, 114
Marble, 7, 8, 9
Market buildings, 138
Masonry, 81, 212, 277, 290, 292
Mass, 2, 3, 148
Masts, 21, 39, 53, 72, 81, 82, 144,
173, 202, 216
Matthiesen, Professor, 7
Matterhorn, 46
Matting, 172
Mattresses, 38
Maxwell, Mr. Hugh, 37
Meat, 12
Mediterranean, 45, 103, 110
Melloni, Professor, 95
Melsen, Professor, 54, 57, 60
Mercury, 9, 172
Metals, 7, 8, 9, 10, 30, 31, 35, 36,
58, 52, 72, 73, 82, 84, 171, 172,
174,185,190,192,194,197,198,
199, 200, 205, 206, 213, 236, 237,
246, 247, 271, 272, 273, 285, 286,
287, 289
Metal points, 232, 233, 234, 236,
237
Mica, 6
Michselis, M., 107
Milk, 12
Mines, 34, 44, 45, 201, 230, 287
Mirrors, 38, 172, 273, 290
Mist, 46, 173
Moisture, 8, 48, 65, 69, 76, 84, 181,
190, 224, 232, 251, 253
Money (in purses), 171
Monuments, 274, 277, 284, 286
Mortar, 173
Mould, vegetable, 67
Mountains, 44, 45, 46, 185
Mountain summits, 46, 168, 183
Municipal authorities, 269
VI AILS, 31, 171, 272
1>I Nelson, Colonel, 12, 73, 128
Newall, Mr., 57, 58, 64
Nickel, 17
Night, 222
Nitric acid, 12
Nitrogen gas, 22
Nollet, Abbe, 31, 49, 77
Non-conductors, 9, 10, 173
Nouel, M., 28
OCCUPIERS of houses, 273, 275
\J Odour, sulphurous, 28 ^
Ohm, Professor, 3, 10, 58
300
INDEX.
Oil, 173
Oil tanks, 73, 172, 206
Openings in buildings, 205
Opposition to lightning rods,
242
Ores, metallic, 7
Organs, 171, 273
Ornaments, 171
Owners of houses, 273
T)ALMIERI, Professor, 26
JL Paper, 7, 8, 9, 10, 173
Paratonnerres, 73, 81, 242
Paralysis, 32
Parchment, 7, 9,
Paris, 22, 45, 60, 75, 89, 90, 99,
100, 116
Parliament, Houses of, 57, 76
Patterson, Mr., 59, 65
Pavements, 183, 184, 187, 235,
277, 278, 285, 286
Paving stones, 173
Pekin, 45
Peltier, Professor, 16, 23
Persons, 31, 32, 36, 37, 38, 39, 45,
196, 216, 217, 218, 289
Peru, 18, 44, 160
Petit, M., 29
Philippine Isles, 44
Pickard, Mr., 47
Pigs, 173
Pinnacles, 274
Pipes, hot- water, 171
Pitch, 6, 38, 173
Plate, terrestrial, 167, 169
Plates, iron pointed, 281
Platina, 9, 59, 60, 63, 64, 171,
250
Plaster, 173
Pliny, 25, 36
Plumbago, 7, 9
Points, 59, 60, 61, 62, 63, 64, 152,
232, 233, 234, 236, 237, 278,
281, 289
Ponds, 172, 181
Pools, 187
Porcelain, 7, 8, 9, 173
Portlock, Col. J., 24, 25
Portugal, 25, 109
Potential, 2, 3, 4, 5, 15, 16, 28,
34, 64, 66, 80, 83, 145, 149, 150,
151, 153, 176, 177, 179, 182,
185, 194, 199, 241
Pouillet, Professor, 10, 11,51,52,
63, 68, 82
Power, 145
Practical measures, 266
Preece, Mr. G. E., 35
Preece, Mr. W. H., 1, 27, 29, 33,
34, 39, 54, 55, 58, 59, 61, 66,
70, 71, 75, 79, 80,84, 115
Press, the, 269
Preservatives, 36
Priestley, Dr., 22, 59
Private houses, 139, 141, 143, 210
Prussia, 43, 144
Public buildings, 210
Pumps, 172
QUANTITY, 23, 145, 148, 149,
151, 153, 176
Quartz, 30
RAILINGS, 171
Eailways, 138, 172, 173, 185,
187, 218, 236
Rain, 12, 28, 80, 168, 172, 221,
224
Rainwater-pipes, 67, 70, 73, 171,
172, 272, 273, 289
R. E. Aide-Memoire, 9, 56, 81
R. E. Journal, 127
R. E. Professional papers, 26
Record of thunderbolt incidents,
267
Registrar-General of England, 39,
40, 41, 42
Registrar-General of Ireland, 4 1
Reily, Mr., 129
Rending force, 193
Repulsion, 1, 5, 146, 225
Reservoir of water, 152, 153
Resin, 7, 8, 9, 10, 30, 47
Resistance, 3, 6, 10, 28, 29, 147,
149
Restrainers, 173, 191
Restraint, 145, 147, 150, 151, 190,
199, 200, 202
Return strokes, 31, 50, 146, 148,
151, 175, 227, 228, 229, 230
Richmann, Professor, 50, 92
INDEX.
301
Riding, 198, 290
Ridges, 171, 172
Riess, Professor, 62
Risca colliery, 46, 287
Rivers, 15, 43, 46, 172, 181, 186,
253, 276
Roberts, Mr., 124
Rocks, 35, 45, 167, 173, 182, 183,
187, 276, 282
Rocky ground, 276, 285
Rods, tie, 273
Roofs, 171, 172, 173, 200, 216, 272
Roget, Professor, 8
Russia, 25, 44
8ABINE, Colonel, 16, 18
Sabrina, isle of, 24
Safes, iron, 273, 290
Salt, 8
Sand, 15, 30, 66, 67, 173, 187
Sap, 30,162
Sash weights, 171
Schelthorn accident, 198
Schleswig-Holstein, 45
Scotland, 88, 98, 103, 125
Sea, 22, 67. 70, 172, 181, 186
Sealskin, 37
Seamen, 39, 53
Secchi, Father, 122
Seneca, 76
Shape of ground, 185
Shaw, Dr., 33
Sheds, 173, 211, 290, 292
Sheep, 173
Shingle, 15, 66, 67, 173
Ships, 51, 52, 53, 70, 79, 172,
173, 181, 194, 202, 212, 246,
248, 263, 288, 289
Ships, H.M., 39, 45, 51, 52, 53,
144, 249, 288
Ships, merchant, 22, 53, 288
Shock, 3, 32, 175, 191
Shutters, 171, 173, 205, 289
Siemens, Dr. Werner, 34
Silk, 7, 8, 9, 10, 38, 173
Silver, 7, 9, 10, 61,64,171,250
Silver, German, 9
Skylights, 173
Slate, 31, 173, 272
Smoke, 7, 9, 172, 207, 231, 235
Smyrna, 25, 44
Snow, 7, 9, 10, 46, 172, 183, 221
Society of Arts Journal, 113,
114
Society of Telegraph Engineers'
Journal, 10, 11, 23, 28, 29, 34,
35, 55, 71, 85, 114, 115, 123,
128
Soil, 174, 187
Soldiers, 218
Soot, 70, 79, 172, 207, 290
Spain, 25, 115
Spence, Dr., 48
Speaking tubes, 171
Spindles, 171, 272, 275
Spires, 22, 31, 54, 81, 137, 138,
139, 140, 141, 142, 143, 144,
173, 193, 200, 205, 272, 273,
274, 278
Springs, 66, 172
Staircases, 171, 173, 273
Statistics, 39, 40, 41, 42, 43,44
Standard newspaper, 17, 25,
26, 46, 90, 92, 104, 116, 121,
132
Statues, 171, 274
Steam, 7, 9
Steel, 17
Steeples, 22, 50
St. Elmo's fires, 21, 22, 175,
234
St. Helena, 44
St. Petersburg, 45, 50, 92
Stobart, Mr. H. S., 121
Stone, 7, 8, 9, 30, 31, 47, 173,
193, 194, 272, 273, 276
Strain, 5
Stores, 274, 275, 284, 286
Straw, 8, 173
Streams, 181, 187
Subterranean thunder, 14, 25
Suetonius, 36
Sun, the, 16, 19, 20
Sun spots, 19
Surface, 150, 151
Surface of the earth, 179, 187,
194, 201, 221
Surfaces, moist, 167, 168
Surfaces, rocky, 167, 168, 184
Survey, electro-geological, 268
Sweden, 44
Switzerland, 43, 93, 107
Symmer, Professor, 50
302
INDEX.
Symons, Mr., 39, 114
Symons 1 Meteorological
23, 116
mABLE-LANDS, 185
J_ Tanfield Moor colliery, 287
Tanks, 67, 68, 181, 253
Tar, 173, 276
Telegraphs, 16, 20, 33, 34, 68,
171, 173, 194, 216, 230, 236,
253
Telegraphic Journal, 10, 11, 17,
19, 24, 28, 56, 59, 62, 68,
76, 84, 98, 99, 105, 106, 110,
111, 112,115, 124
Temperature of the air, 222
Tents, 37, 211
Terra cotta, 173, 272, 273
Testings, 75, 76, 255, 256, 257
Theory, 26-5
Thickness 150, 151
Thomson, Sir William, 10, 15,
17, 19, 20, 265
Thorns, 62, 233
Thunder, 22, 2o, 28, 44, 46, 47
Thunderbolts. 26, 27, 28, 36, 42,
85, 156, 175, 176, 177, 187, 221,
230, 275, 288, 291
Thunderclouds, 13, 14, 15, 23, 27,
32, 35, 50, 60, 63, 70, 165, 180,
183, 189, 233, 234
Thunderstorms. 10, 12, 13, 14, 15,
21, 22, 24, 31, 33, 34, 37, 38,
44, 45, 46, 154, 159, 226, 290,
291
Tie rods, 289
Tiles, 173, 272
Tillard, Captain, 24
Time, 2, 3, 148
Times newspaper, 79, 124, 125,
126, 127, 129
Tin, 6, 9
Toaldo, Professor, 72
Tomlinson, Mr., 118
Tools, 292
Towers, 137, 139, 141, 142, 143,
144, 200, 205, 273, 274, 278
Towns, 45, 184, 210, 218, 235,
269, 270, 276
Town-halls, 54, 60, 65, 137
Town houses, 276, 287
Trees, 30, 35, 37, 43, 70, 81, 173,
193, 194, 215, 276, 290, 291
Truenfeldt, Mr. Von, 29
Turrets, 273, 274
Tylney, Lord, 89
Tyndall, Professor, 6, 8, 21, 22,
31, 32, 47, 48, 49, 50, 51, 62, 63
TTNDERGROUND sites, 285
U Underground vaults, 36,
290
Umbrellas, 290
Uplifting force, 191, 192, 193
TTAILLANT, Marechal, 52
V Valetta, Signer, 25
Valleys, 186, 187
Valves, terrestrial, 235
Vanes, 171, 272, 274, 275
Vapour, 7, 9, 22, 23, 173
Varley, Mr. S. A., 34
Vaults, 36, 290
Vegetable bodies, 7, 8, 9, 10, 173
Vegetation, 11, 173, 182
Velocity, 3, 148
Ventilators, 171
Vesuvius, Mount, 24, 25, 26
Vines, 222
Viollet-le-Duc, M., 81
Volcanic eruptions, 17, 24, 25, 26,
156, 160. 269
Volta, Professor, 11, 32, 38, 239
Von Guericke, Otto, 47
Von Yelin, Herr, 116
WALES, 40, 41, 42
Walker, Mr. C. V., 17
Walking, 198, 290
Walking sticks, 173, 290
Wallace, Mr., 125
Walls, 38, 72, 203, 206, 290
Ward, Dr., 47
Warehouses, 274, 275, 284, 286
War Office instructions, 6, 15, 30,
31, 35, 51, 55, 56, 62, 66, 67, 68,
71, 72, 75, 80, 81, 123
Watches, 171
Water, 6, 7,9, 10, 11, 14, 15, 35
67, 68, 69, S3, 180, 251, 276
INDEX.
303
Water, head of, 3, 153
Water, rain, 8, 172
Water, sea, 8, 172
Water, spring, 8, 172
Watersheds, 185
Waterspouts, 22, 23, 206, 290
Watson, Dr., 48, 49, 50, 52, 92
Weather, 10, 11, 222
Weathercocks, 171, 200, 272, 274
Weissenborn, M., 29
Wells, 66, 68, 69, 172, 187, 253
Wellington Weekly Gazette, 121,
126, 130
Wellsted, Mr., 131
West, Mr., 102
West Indies, 89, 95
Western Morning News, 106, 108,
120, 121, 129, 130, 131
Western Weekly News, 110, 115,
119, 120, 131, 132, 133
Wheatstone, Sir Chas., 6
Wheel tires, 172
Whirlwinds, 23
Whymper, Mr. E., 46
Whyte, Mrs., 125
Wilson, Mr., 49, 77
Wind, 13, 44, 84, 225, 284
Windows, 171, 173, 205, 273, 290
Winter, 222
Winthrop, Dr., 37
Wires, 30, 192
Wire guards, 273
Wood, 7, 8, 9, 10, 30, 82, 173, 194,
206, 272, 288, 290
Wooden ships, 288
Woodwork, 192, 193, 216
Woodman, Mr. N., 124
Wool, 8, 173
Work, 3, 148, 176
ZINC, 6, 9, 171
ZoUner, Dr., 24
Zurich, 81
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