QC 
 
 76 
 
 UC-NRLF 
 
J REESE LIBRARY 
 
 \\J * * . * . OF THE 
 
 UNIVERSITY OF -CALIFORNIA 
 
 Received 
 Accessions No..-3A&6.3.-' Shelf No. 
 
THE RAINBAND IN SPECTROSCOPE 
 OF MODERATE DISPERSION. 
 
 A aB C 
 
 !! I 
 
 
 E b 
 
 
 StanfardJs Geogl- Estab*. 
 
A PLEA FOR THE RAINBAND, 
 
 AND 
 
 THE RAINBAND VINDICATED, 
 
 BY 
 
 J. RAND CAPRON, F.R.A.S., F.RMET.Soc. 
 'UNIVERSITY 
 
 LONDON : 
 EDWARD STANFORD, CHARING CROSS, S.W 
 
LIST OF ILLUSTRATIONS. 
 
 The Rainband in Spectroscope of moderate dispersion.. Frontispiece. 
 Rain and Rainband Diagrams, 1880 aud 1881 ...... Plate I. to face page 8. 
 
 Monthly Rainfall and Rainband, 1882-3 ...... II. 20. 
 
 Rainfall and Rainband at Guildown for four consecu- 
 
 tive months of 1881 .............. ,, III. 21. 
 
 Ozone and Rainband at Guildown for four months of 
 
 1882 .................... IV. 22. 
 
 Pocket Spectroscope ... ... .. ... ... Fig. 1, page 15- 
 
 The Standard Spectroscope (exterior) ......... ,, 2 ,, 17. 
 
 ,, ,, (interior) ......... 3 17. 
 
 Double Slit Plate ................... 4 ,, 18. 
 
 Double Spectrum ... ... ... ... ... ... ,, 5 ,, 18. 
 
 Kinkerfues Weather Compass ............ ,, 6 23. 
 
 Electrometer and Battery (plan) ............ ,, 7 ,, 26. 
 
 ,, ,, (elevation) ... ..... ,, 8 ,, 26. 
 
 Collecting Apparatus .. ... ... .. ... ,, 9 ., 28. 
 
PKEFACE. 
 
 " A PLEA FOR THE EAINBAND " was originally published in Symons's 
 Monthly Meteorological Magazine for December, 1881. 
 
 It subsequently, as a separate pamphlet, attained a considerable 
 circulation, and though by no means the earliest treatise in which 
 the subject is dealt with, was probably the first to bring it in a mono- 
 graph form before the general public. It has, however, lately been 
 out of print. Four years since its appearance, that is to say in the 
 October and November numbers of the present year, it has been 
 followed by a second article in Symons's Magazine, entitled " The 
 Rainband Vindicated." As " The Plea 5 ' is still frequently asked for, 
 and the second article is really a continuation of the first, it has been 
 determined to publish the two together, so that those who wish for 
 information may have the subject before them as a whole. 
 
 " The Plea " (Part I.) is reprinted, except that it has been slightly 
 condensed. The original lithographic plate of " The Rainband as 
 seen in a Spectroscope of moderate dispersion,'' has been revised and 
 redrawn. " The Rainband Vindicated " (Part II.) is a reprint of the 
 article as it appears in the Magazine, with the same plates and wood- 
 cuts. Since its publication, it has received corroboration in the 
 shape of "Tables of the Climate at Falmouth for the years 1883 and 
 1884," kindly sent to me by Mr. Wilson Lloyd Fox, F.R.Met.8. 
 Mr. Fox, in these tables gives the sums of his daily rainband observa- 
 tions when compared with rainfall as follows : 
 Means of last four months of year 1883 
 
 Rainband, 49. Rainfall, 5'170 inches. 
 Means of twelve months of year 1884 
 
 Rainband, 37. Rainfall, 3'141 inches. 
 
 His scale runs from to 4. Two letters on "Atmospheric Elec- 
 tricity at Guildown," were also published in S-ymms's Magazine for 
 August and October, 1 885. A reprint of these has been added by 
 way of Appendix, for the use of those who desire to take up the 
 subject more fully. 
 
IV. PREFACE. 
 
 In them are described and figured the necessary apparatus for col- 
 lecting and testing atmospheric electricity, and the methods of using 
 them. Those who are disposed to make further research into the 
 subject of Ozone are advised to consult Dr. Cornelius B. Fox's 
 " Ozone and Antozone " (Churchill, 1873), which contains a full de- 
 scription of its properties, and the tests by which its presence and 
 quantity in the air may be recognised. The Klinkerfues Weather 
 Compass (with instructtons for its use) can be obtained from Messrs. 
 Biernatzki and Co., Hamburg, the patentees, and from Mr. John 
 Browning, 63, Strand, London. A short index of principal matters 
 has been added. 
 
 The Eainband, Atmospheric Electricity, and Ozone are, it appears 
 to me, all subjects legitimately and closely connected with Meteor- 
 ology ; and yet for various reasons they hardly seem to have hitherto 
 received from observers their fair share of attention. My object in 
 writing these articles will have been accomplished if I succeed in 
 drawing to them more of this attention, and in exciting in them such 
 an interest as will stimulate their more extended investigation. 
 
 J. R. C. 
 
 Guildown, 
 January, 1886. 
 
PART I. 
 
 A PLEA FOR THE RAINBAND, 
 
 WHAT is the rainband 1 I will describe the rainband as a dark band 
 or shading (or rather, under sufficient amplifying power, set of fine 
 lines) seen on the less refrangible (red) side of the double line D in 
 the atmospheric spectrum ; and the presence or absence of which is 
 indicative of the presence, or otherwise, of moisture (more strictly 
 speaking) excess of moisture in the atmosphere Its history may be 
 said to date from the time when Angstrom's maps of the solar lines 
 were found to present different aspects according to the condition of 
 moisture of the atmosphere at the time of observation, and when 
 that early spectroscopist proved the presence and absence of certain 
 lines forming bands in the spectrum, more especially a set near D, 
 to depend on that condition. No practical meteorological result fol- 
 lowed, however, until, as Prof. Piazzi Smyth tells us, the subject was 
 first presented to him as a marked feature in sky spectrum at 
 Palermo before and after a sirocco in 1872. Next, when in July, 
 1875, destructive floods in both France and England (not predicted by 
 the barometer) were noticed by him in connection with a peculiar band 
 in the spectrum under dates July 19th and 26th, 1875. Prof. Smyth 
 vividly describes in Nature (vol. xii., pp. 231, 252) the phenomena 
 then observed, how the dark band near D was found the forecast of 
 a drenching afternoon following the fine opening of a Scotch holiday 
 in Edinburgh ; and how, on another occasion, it became the " spec- 
 troscopic provision of rain with a high barometer." Then followed 
 observations in May, 1876, to the same effect in France, especially at 
 Marseilles, where the rainband was seen in the spectrum, and fol- 
 lowed by rain to the surprise of the natives, who consulted only the 
 public barometer and thermometers, and found none predicted. In 
 February, 1878, appeared the fourteenth volume of the Edinburgh 
 Astronomical Observations, 1870-1877, and here, under the head of 
 " Meteorological Spectroscopy in the small and rough," we have the 
 subject treated in a most complete and elaborate manner, and illus- 
 trated by a set of engravings of spectra. The Scottish Meteorological 
 Society's Journal, N.S., Nos. li., lii., also contain contributions by 
 Prof. Smyth on the subject. Again, in Nature, of July 1st, 1880, 
 vol. xxii., pp. 194, 5, the subject of "rainband spectroscopy " is dealt 
 with in a condensed and epitomized form very acceptable to the 
 reader, who, doubtless will recognise the identity of the " Edinburgh 
 experimenter " in this useful contribution on the subject. 
 
For rainband observation a spectroscope is necessary. 
 
 A large one with several prisms is desirable, if the ultimate com- 
 position of the band or bands is to be examined ; but for ordinary 
 meteorological purposes, and to observe the general character of the 
 band near D, a pocket or miniature instrument is quite sufficient, 
 indeed best adapted. This may be obtained from any scientific 
 optician, and will cost, according to construction, from one to three 
 guineas. The more expensive ones have an adjustable slit and 
 achromatic lenses ; but these are not necessities, and the cheaper 
 form is nearly as useful. 
 
 I employ for my own observing a McClean's star spectroscope with 
 a slit arrangement adapted, which makes also an efficient instrument 
 with rather a larger spectrum than the pocket spectroscope. 
 
 Having obtained the instrument, nearly close the slit and adjust 
 the focus till the lines in the solar spectrum are sharp and clear. 
 This should be done on a bright part of the sky. Then point the 
 instrument to the quarter of the heavens which it is desired to 
 examine, and note results as to, especially, lines D and their neigh- 
 bourhood. 
 
 I generally observe thus at 9 a.m. daily from my laboratory 
 window (looking towards the south), but if time and opportunity 
 allow three observations, at 9 a.m., 1 p.m. and 5 p.m. would be 
 better, varying the parts of the sky tested ; and I examine with the 
 spectroscope elevated about 13 degrees. Prof. Smyth recommends 
 to point as low as you can to the horizon provided you get trans- 
 mitted light, and to observe when the sun is neither high nor low. 
 I find in practice 9 a.m. (the same hour when my other instruments 
 are observed) a good time to make the observation when only a 
 single one is taken daily, and also that if I get too low on the hori- 
 zon I am apt to have always a " rainband," or rather a false band 
 due to earth moisture. In observing you will soon remark changes in 
 the characters of some of the spectrum lines, as compared with these 
 when seen on a blue sky with an elevated spectroscope, and, more- 
 over, bands of varying intensity are found added to the low spectrum 
 not seen in the higher one. The lines and bands that change their 
 character, or are variable in their appearing, are telluric ; either rain- 
 bands or lines, called by Prof. Smyth a " function of moisture and 
 temperature," or low sun bands and lines distinguished by him as "a 
 function of dry air and low sun." The true solar lines remain un- 
 changed. Prof. Smyth, in the Edinburgh volume before referred to, 
 fully describes, both in type and by illustrated drawings, all these bands 
 and lines and their changes, and points out that there are several 
 smaller rainbands besides that near D. In practice it will, however, 
 generally be found sufficient to examine the principal one on the 
 red, or if you have the spectrum as I do (with the red end of the 
 spectrum to my left hand), left side of D. An examination of the 
 other lines, though desirable for special purposes, will only tend to 
 confuse the general observer. Prof. Smyth recommends, and has 
 used a dry air band on the right hand side of D as a standard of 
 
comparison with the rainband ; but I have not often myself made 
 use of it, judging independently by the rainband itself. 
 
 In enumeration of the darkness of the band, for the purpose of 
 record, I use from No. 1 to 5, as under : 
 
 1 means faint. 
 
 2 faint to moderate. 
 
 3 moderate. 
 
 4 moderate to strong. 
 
 5 strong. 
 
 1 to 10 is the enumeration recommended and employed by Prof. 
 Smyth. I found, however, the dividing into so many degrees was 
 difficult, especially when the intensity is slightly changing by passing 
 clouds. Simultaneous observations should if practicable be made 
 and recorded, of barometer, wet and dry bulbs, and wind (force and 
 direction) ; and the circumstances of sun, sky and cloud at the time 
 should be shortly noted. 
 
 Ozone test papers may also be usefully referred to, as cold winds 
 alike affect them and rainband readings. The D lines are generally 
 more or less involved in the rainband shading. 
 
 To enable the observer to judge of the general appearance and in- 
 tensity of the larger rainband near D, I have given (see frontispiece) 
 some drawings of spectra as seen in the McClean spectroscope, of 
 which the following is a description : 
 
 (1) Spectrum as seen upon a pure high sky, showing principal 
 solar and telluric lines in their proper positions, and with their de- 
 signations, but not showing the finer lines between, nor any bands. 
 
 (2) Spectrum observed January 17th, 1881, 8 a.m. Morning dull; 
 red sunrise ; low sunbands and lines (note especially band to right of 
 D) strong. No rainband. 
 
 (3). Spectrum observed 24th August, 1881, 8 a.m., showing 
 moderate low sunbands and lines, and a, faint rainband with rain 
 lines showing through. 
 
 (4) Spectrum seen November 16th, 1880, 1 p.m. Eain and wind, 
 but clearing in some parts of the sky. Low sunbands and lines 
 weak. Rainband moderate. 
 
 (5) Spectrum seen December 9th, 1880, 8 a.m.^,Sun shining 
 through watery clouds ; low sun lines strong. Rainband strong. 
 
 (6) Spectrum seen July 6th, 1881. Rainband everywhere, and 
 exceptionally strong, stretching nearly half way between C and D. 
 Whole spectrum darkened and obscured. 
 
 The above-described drawings do not give, except in a rough way, 
 the details of the lines and bands other than the rainband, which is 
 situated to the left of the double line D, and has its place marked by a R. 
 
 Spectra 2, 3, 4, and 5 are meant for observing by, as representing : 
 2, none ; 3, faint ; 4, moderate ; and 5, strong. Rainband faint to 
 moderate, and moderate to strong (the intermediate intensities) can 
 be estimated, and in practice the eye and judgment will soon be 
 found to accommodate themselves to the graduations 1 to 5. 
 
8 
 
 Before proceeding to the questions affecting the rainband's value 
 to forecast rain, it may be desirable at once to say that it does not 
 claim absolute infallibility as to time and quantity of rain to follow, 
 though Prof. Piazzi Smyth believes "it is never really absent when 
 rain is imminent." 
 
 How its appearance and indications may be modified will be re- 
 ferred to later. 
 
 Its action is hygrometric, and involves the general principle that 
 according to the amount of suspended moisture in the air, so are its 
 appearance and strength. A faint, or faint to moderate, rainband, 
 may in some cases only show an amount of moisture which will 
 remain suspended for some time. A moderately strong or strong 
 rainband, represents an excess of suspended moisture, which before 
 long is sure to descend. Prof. Smyth mentions instances, and I have 
 met with them myself, where an apparently perfectly transparent sky 
 showing rainband has, on a change of temperature, condensed, as it 
 were into clouds, which have poured. 
 
 A little while since (August, 1881) I observed only a faint, or at 
 most faint to moderate, rainband in the morning at 9 a.m., on a 
 beautiful blue sky, studded with white cauliflower innocent-looking 
 cumuli. I predicted wet, and at the mid-day meal was twitted with 
 the sunshine and the brightness, but sure enough in the afternoon 
 down came the rain. On the other hand it will sometimes be raining, 
 and yet only a slight rainband shows, an effect generally connected 
 with a cold wind N. or E. No rainband is also sometimes observed 
 when the wet and dry bulb readings only slightly differ, but the ex- 
 planation of this may be that low earth moisture affects the bulbs, 
 which is not recognised in the sky-directed instrument looking through 
 a thin stratum of it. 
 
 In order to illustrate the practical working of the rainband, I have 
 prepared the diagrams on Plate I, which show graphically by 
 line lengths the rainband and rainfall during two periods of 1880 and 
 two of 1881. The rainfall is represented by vertical lines, in which 
 each one-tenth inch is one-tenth inch rainfall ; the rainband by similar 
 lines, in which each one-tenth inch is one of the scale 1 to 5. The 
 rainband was observed daily at 8 a.m. in 1880, and 9 a.m. in 1881. 
 The rain represents the fall during the 24 houi's following the rain- 
 band observations, so that where the lines correspond the rain 
 follows the rainband within that period. 
 
 The general result of these diagrams is to show that the rainband 
 predicts and also accompanies the rain, and to a certain extent cor- 
 responds in strength with the predicted rainfall. There are discre- 
 pancies and irregularities in most of the diagrams, it is true, some of 
 which are to be explained and accounted for by incidental circum- 
 stances, the particulars of which I take from notes made at the time, 
 and others (such as cases of rain at night after faint rainbands in the 
 morning) by the interval of time elapsing between the spectroscopic 
 observation and the rainfall, it sometimes happening that the rain- 
 band will much change its intensity during three daily observations 
 

On the other hand, occasionally the rainband will precede the rain 
 by a day or two. 
 
 Diagram 1 July 21st to August 2nd, 1880. This diagram repre- 
 sents a set of rainbands, of which moderate to strong is the highest 
 figure, leading up to a moderate rainfall. July 25th appears as ex- 
 ceptional in the absence of the band. The day was fine and hot, and 
 the rain fell during the night with a change of wind from W. to S. 
 This fall ('35) was, however, shown to be in prospect by the bands 
 on the 22nd, 23rd, and 24th, gradually increasing in intensity from 
 faint to moderate. 
 
 Diagram 2 September 16th to October 13th, 1880. The first and 
 last sets of lines agree fairly. The heavy rainfall of the 18th (nearly 
 an inch) was forecasted by a strong rainband the day before, which 
 was reduced to moderate during the fall itself, and as the rain passed 
 away so did the rainband diminish in intensity, dropping to faint on 
 the 19th, for -20 of rain. On the 10th of October a strong rainband 
 was only followed by a small rainfall, but the wet and dry bulbs 
 were but 2 apart, so that much suspended moisture must have been 
 in the lower atmosphere, and in fact on the 13th some more rain 
 fell. In the centre of the diagram we have six rainbands (five faint 
 and one moderate) with only a slight rainfall. The following figures, 
 however, show for the five days on which these rainbands appeared 
 the differences in the wet and dry bulbs. 
 
 1880. Sept. 21. -2 
 22. 4 
 
 At 8a.m. 
 
 26 2 -5 
 27. 3 ) 
 
 The following passages also appear in my journal at this time : 
 " The main feature of the week has been the persistent heavy morn- 
 ing and evening mists," and again (after quoting the above figures) 
 " so that the air has been kept in a chronic state of saturation," a 
 condition quite sufficient to account for a faint rainband. While on 
 the subject of this diagram it may be mentioned that space would 
 not allow, otherwise I should have given in a graphic form the rain- 
 band and rain lines from 8th to 15th September, 1880, as they well 
 illustrate how a strong rainband (on the 9th) came before very heavy 
 rain on the llth, while pending the actual rainfall the band was 
 moderate, and at last even faint. I insert instead the following 
 tabular particulars : 
 
 Rainband. 
 
 None. 
 
 Strong. 
 
 Faint. 
 
 Moderate. 
 
 Moderate. 
 
 Faint. 
 
 Faint. 
 
 Faint. 
 
 Date. Rain. 
 
 1880. Sept. 8th . 
 
 ... -oo 
 
 
 9th . 
 
 ... '04 
 
 
 10th -. 
 
 00 
 
 
 llth . 
 
 .. 1-58 
 
 
 12th . 
 
 54 
 
 
 13th . 
 
 ... 1-19 
 
 
 14th . 
 
 ... 1-48 
 
 
 15th . 
 
 ... 113 
 
10 
 
 We thus see that the rainband indicated the finely-divided trans- 
 parent moisture ready to collect and fall as rain, and also showed 
 itself upon the saturated air and warm morning mists (wind mostly 
 S. and S.W.) above referred to, while it only moderately or faintly 
 appeared during the heavy rain itself. 
 
 One explanation of this peculiar phenomenon of a low number 
 rain-band on falling rain may be that, pending heavy rainfall, the 
 whole spectrum is more or less obscured, and thus the rainband 
 shading near D, for want of contrast is less observed. We shall see 
 later that it does appear strong on a light misty rain. 
 
 In connection with this diagram it may be further pointed out 
 how a distinction lies between warm mists and cold fogs in the rain- 
 band's behaviour. The mists before spoken of were warm ones, and 
 a rainband, though faint, appeared almost without exception upon 
 them, but at a later period (in October) partly shown in the same 
 diagram, there were cold foggy mornings with N. wind, during which 
 the band was absolutely and persistently nil. 
 
 It results from these observations that the rainband is less reliable 
 in winter than in summer for indicating a rapid following of rain, 
 and we can understand this in the fact that watery particles may 
 remain without precipitation in a cold and comparatively even 
 temperature in winter, while they will quickly descend from a warm 
 air in summer, as the result of a fall of temperature. 
 
 We now pass to diagram 3, representing rain, and rainband 
 from May 16th to June 8th, 1881, and to Diagram 4, which gives a 
 two months' comparison of rainband and rain viz., from 20th 
 January to 20th March, 1881. The relative periods of rainfall and 
 rainband agree fairly well in these two diagrams, and in some 
 instances (June 5th, 6th, and 7th, and January 27th, 28th, and 29th) 
 the intensities agree, but the peculiar feature about the diagrams 
 is a certain number of strong, or moderate to strong rainbands, 
 coinciding with a very disproportionate amount of rainfall (see 
 especially dates February 4th and 14th and March 9th, when rainfall 
 was only -02, '05, and -02). 
 
 To be also noted is March 10th, when rainband 4 had no rain to 
 follow, and where the observation is marked, " Sunshine through 
 Clouds," and January 26th, rain -40 with no rainband. On this last 
 occasion there must have been more snow and sleet than rain (with 
 wind N., and temperature 29 for maximum) which melted in the 
 gauge. By the 27th the wind had changed to S. and a faint rain- 
 band appeared with rain !!. 
 
 The strong rainbands before mentioned as accompanied by so little 
 rain, being exceptional to the general rainband rules, I have tabu- 
 lated, for comparison, all the cases (7) of No. 5 (strong) rainband 
 between 1st January and 1st July, 1881, as under : 
 
11 
 
 Table shewing circumstances of all strong Eainbands (No. 5), between 
 January 1st and July 1st, 1881. 
 
 
 
 
 
 W.&D. 
 
 
 
 
 
 
 No. 
 
 Date. 
 
 Bar. 
 
 Ther. 
 
 Bulbs. 
 Diff. 
 
 Wind. 
 
 Rain. 
 
 band. 
 
 Ozone 
 
 Notes, 9 a.m. 
 
 1 
 
 Feb. 4th 
 
 29-33 
 
 46 -0 
 
 o 
 
 8. 
 
 02 
 
 5 
 
 4 
 
 Clouds 10. Rain. 
 
 2 
 
 10th 
 
 29-00 
 
 49 -5 
 
 5 
 
 S.W. 
 
 16 
 
 5 
 
 8 
 
 Clouds 10. Rain. 
 
 3 
 
 ,, 14th 
 
 29-60 
 
 38 -0 
 
 2 -5 
 
 s. 
 
 05 
 
 5 
 
 6 
 
 Clouds 10. Dull. 
 
 4 
 
 ,, 15th 
 
 29-64 
 
 38 -0 
 
 5 
 
 S.W. 
 
 25 
 
 5 
 
 5 
 
 Clouds 10. Rain. 
 
 5 
 
 Mar. 9th 
 
 29-83 
 
 48 -0 
 
 o 
 
 w. 
 
 02 
 
 5 
 
 7 
 
 Dull heavy rain. 
 
 6 
 
 May llth 
 
 29 "06 
 
 53 '3 
 
 3 
 
 w. 
 
 08 
 
 5 
 
 8 
 
 Raining. 
 
 7 
 
 26th 
 
 2976 
 
 61'0 
 
 3'0 
 
 w. 
 
 12 
 
 5 
 
 4 
 
 Overcast, slight 
 
 
 
 
 
 
 
 
 
 
 mist, no rain. 
 
 These records present as peculiar features, barometer generally low, 
 difference in wet and dry bulbs slight, wind S. and W., rain minute 
 in quantity (except the 15th with J of an inch), and ozone mostly 
 strong, while in five cases out of the seven rain was falling at the time 
 of observation. One can understand moderate rainbands accompany- 
 ing the really moderate rainfalls of the half-year in question, but the 
 above seem anomalous. A possible explanation is afforded by the 
 strong air saturation at low level, indicated by the slight differences 
 in the wet and dry bulbs, and the probability that the rain so small 
 in quantity, was in quality of the misty drizzling character containing 
 minutely divided particles, which is favorable to the strong enforce- 
 ment of the moisture bands in the spectrum. 
 
 I add a few general instructions and hints which may be useful to 
 observers. 
 
 (1). Occasionally look to your instrument and see that the prisms 
 and lens are clean, and remove any dust from the slit. This last 
 should be done with a camel's hair pencil. 
 
 (2). Distrust observations and reports made by assistants or friends 
 who are not practised in spectroscopic work. I have known dust 
 accumulated on the face of the prism give a false obscurity to the 
 spectrum ;* persons (scientific and otherwise) who never could see a 
 rainband at all ; others who insisted on the horizontal dust lines as 
 rainbands, and even well-practised observers differ very widely in 
 strength estimates (a matter which may possibly affect my own 
 diagrams). 
 
 (3). Observe generally at the altitude which you may have selected 
 as a standard, but do not altogether confine yourself to this, and 
 note : 
 
 * To guard against this I cement a plate of microscopic glass over the eye- hole 
 of the spectroscope. 
 
12 
 
 (a) If the rainband is strong on the horizon and weakens 
 towards disappearance (or nearly this) at 15 or 20 degrees 
 above, distrust it as a prognostic of rain. 
 
 (b) If strong on the horizon, and still strong at the height 
 
 above mentioned, trust it as a prognostic. 
 
 (c) If strong on the horizon, above, and also to the zenith, or 
 
 nearly so, then, as Professor Smyth says, "Beware!" 
 He had only known two such instances (at the time he 
 was writing) and deluges followed. 
 
 (4). A rainband will sometimes shew at the same time, of varying 
 intensities on sky, clouds, and breaks in clouds. The respective 
 intensities should be considered and valued in relation to the 
 character of the various objects examined, e.g., I observed, on an 
 occasion this summer (1881), at 9 a.m., a faint (No. 1) rainband on 
 an apparently perfectly pure blue sky, and a stronger one (moderate 
 No. 3) on some by no means dangerous looking clouds floating in it. 
 Rain soon came, and I have no doubt both sky and clouds were 
 nearly equally charged with moisture, though under different con- 
 ditions. 
 
 (5). The solar lines in the spectrum may be brought in aid in ob 
 serving. When these are bright, clear, and sharp, rainband is usually 
 absent ; when they are obscure and seen faintly, rainband is generally 
 present. A lady, who assisted me in observing, used to judge with 
 success by the appearance of these lines when she felt in doubt about 
 the rainband itself. 
 
 (6). The general rules of conduct of the rainband may be summed 
 up as follows : 
 
 (a) It indicates an excess of moisture in the air (often in- 
 
 visible) and presages according to its intensity, sometimes 
 upon a clear, and sometimes on an opaque sky, the coming 
 of rain and its quantity. "It is strong when the air is 
 saturated with moisture ready to fall." (Piazzi Smyth). 
 
 (b) When the actual rain comes, the band frequently drops 
 
 in intensity, sometimes becoming even quite faint during 
 heavy rainfall. In summer, during a warm wind, a pro- 
 nounced rainband will accompany rain. If the two last 
 are not found together, it is during the prevalence of 
 cold winds. In winter, a moderate rainband may be 
 observed for some time, and yet rain does not fall. This 
 is found during the presence of a warm wind, which 
 holds the air moisture in suspension. Upon change to a 
 cold wind, rain follows. 
 
 (c) A long continued faint, or faint to moderate rainband is 
 
 pretty sure to be followed by rain, generally in quantity. 
 
(d) A faint, or perhaps faint to moderate rainband may be 
 often seen upon fog or mist. It does not necessarily 
 presage rain, unless it increases to strong, which it 
 seldom does. If the sky above fog or mist be clear, the 
 spectroscope should be elevated to examine this as the 
 test for the rainband true. 
 
 (7). Ozone and rainband are usually in accord with one another, 
 both weak during cold winds and cold fogs, and both strong during 
 warm winds and warm mists. Observations on the electric condition 
 of the atmosphere might be usefully combined. 
 
 Lastly. Observers should not be discouraged if the rainband pre- 
 dictions are not always immediately and exactly fulfilled. If there 
 were but one form of rainband, and one condition of moisture in the 
 air, we might get the formula : Rainband =r rain ; no rainband = 
 no rain, in all cases ; but this is far from the fact. The spectroscope 
 is a delicate instrument of research, and the intensity of the rainband 
 admits of degrees which maybe considerably modified by, (1) cir- 
 cumstances of observing, such as width of slit, altitude of spectro- 
 scope, time of day, and part of the sky examined ; (2) conditions of 
 the matter examined in its graduations of transparent vapour, mist, 
 cloud, and rain (the size and proportion of the aqueous particles 
 varying in each) ; and (3) by other meteorological conditions and 
 especially that of temperature, as largely affecting the quantity of 
 moisture held in suspension. 
 
 If the character of the band is liable to be thus modified, the judg- 
 ment to be formed as the result of its examination must be neces- 
 sarily applied with caution, and with due regard to the probable 
 effect of these modifications. 
 
 J. RAND CAPRON, F.R.A.S. 
 
 Guildown, Nov. 1881 
 
14 
 PART II. 
 
 THE RAINBAND VINDICATED, 
 
 IT is now some four years since that in the pages of the Meteorological 
 Magazine I essayed to give a popular character to a comparatively 
 unknown branch of science in my " Plea for the Rainband." 
 
 Has this plea been successful, and has the rainband vindicated its 
 position as a weather prognostic 1 I venture to think that both 
 these questions may be answered in the affirmative. Soon after the 
 publication of the article, I was requested by a well-known optician 
 to permit a reprint of it as a companion to the spectroscope, and 
 before long many copies of it were distributed amongst meteorologists 
 and others. This brought the matter before the public, and not 
 long after rainband spectroscopes, pamphlets, and discussions showed 
 that a keen interest was felt in the subject. 
 
 Of course, as in the case of all other new objects, the first rush for 
 information and possession by and by passed, and the interest in 
 it to a certain extent subsided. I have recently found, however, 
 from enquiries and correspondence addressed to me, that this, though 
 diminished, has by no means died out. I propose, therefore, to 
 justify what the "Plea" advanced by shortly stating the subsequent 
 progress of rainband spectroscopy to the present time. 
 
 The impetus given to the enquiry may be recognized in three 
 ways: by (1) its recent literature; (2) the increased use of the 
 spectroscope as a meteorological adjunct ; and (3) recorded observa- 
 tions and their results. 
 
 THE RECENT LITERATURE. 
 
 In taking up the first subject, the recent literature of the rain- 
 band, I propose to deviate somewhat for the purpose of introducing 
 an interesting early notice of it which escaped my attention when 
 writing my " Plea," and which it would be unjust now to omit. It 
 dates back as far as 1869, and will be found in the Meteorological 
 Magazine for July and October of that year, vol. iv. Nos. xlii. and 
 xlv., " The indications of the sky." The first part of this article 
 describes and figures Saussure's cyanometer and its mode of use, and 
 then after quoting Kaemtz on the blue colour of the air comes the 
 following passage : " In spite of ourselves the above extract has led 
 from the original subject of this article, the cyanometer, to what 
 must, we presume, be held to be its legitimate successor, the spectro- 
 scope." The second part of the article treats of the spectroscope and 
 its advantages to meteorologists, and by an extract from the British 
 
15 
 
 Association Report for 1868, "Observations on the atmospheric 
 lines of the solar spectrum in high latitudes, by George Gladstone, 
 F.C.S., F.R.G.S.," it points out the distinction between " atmospheric" 
 and " solar " lines, and shows how these former are always most pro- 
 minent with a low sun, while scarcely visible with a high one. Also 
 that the red end of the spectrum varies under similar circumstances 
 in length and brilliancy. Prof. Roscoe's " Spectrum Analysis " is 
 quoted, a figure of a pocket spectroscope (reproduced here, Fig. 1) is 
 
 Fig. 1. 
 
 given, and the article ends thus : " No one can tell what secrets lie 
 hid in these atmospheric lines, but to us it seems that by their careful 
 and systematic observation the ' Message from the Stars ' which has 
 taught us so much may be rivalled in practical importance by a 
 'Message from the Sky.' " 
 
 This prediction may not have caught the full import and meaning 
 of the atmospheric bands and lines, but at least it forecasts the value 
 they subsequently attained in meteorology. 
 
 Passing from this, we will refer to a correspondence in the Times, 
 which took place in the latter part of 1882, and in which both sides 
 of the question were jealously advocated. Prof. C. Piazzi Smyth 
 here pens a series of letters in favour of the rainband. In one of 
 these he states he saw a spectroscopic rainband, " the blackest and 
 most intense of the season," and " destructive floods followed." As 
 the rainband cleared away, " magnificent harvest days followed. ' 
 Mr. Ralph Abercrombie sees no value in the rainband, and pins his 
 faith upon " isobaric lines," and the forecasts of the Meteorological 
 Office derived therefrom. The Duke of Argyle in a yachting cruise 
 could not see that the rainband had any predictive value, and thinks 
 Prof. Smyth's case was a " good shot." Per contra, Mr. Cory, F.M.S., 
 contends for the value of the rainband, and gives reports of a series 
 of observations proving his case. Agricultor (in the English 
 Mechanic) " has been much struck by the accuracy with which the 
 rainband appearance predicts coming rain." 
 
 Mr. Abercrombie's isobars are most amusingly discounted by Sir 
 Edmund Beckett in a letter containing a long list of official weather 
 prophecies and their want of fulfilment, and recommending " a return 
 to Zadkiel." In June, 1883, my weekly weather report to the 
 Surrey Advertiser contained the following : " Of these rainfalls, the 
 only indication was the rainband, the barometer throughout standing 
 fairly high (between 29-84 in. and 29-99 in.)" Thus the public prints 
 not only took an interest in, but on the whole supported the rainband 
 theory. 
 
16 
 
 As observers and observations increased, more solid literature was 
 developed, including : Nature, vol. xxvi., pp. 552-4, " Spectroscopic 
 Weather Discussions," by Prof. C. Piazzi Smyth, in which the whole 
 subject is reviewed in a condensed form with instructions to observers, 
 and illustrated by two diagrams of the D part of the solar spectrum 
 under considerable dispersion, the one taken in August, 1882, under 
 moist air conditions, and the other on September 4th, 1882, after 
 a whole week of very dry weather. In this article it is shown 
 that, apart from the spectroscope, the wet bulb difference only 
 slightly indicated the sweeping away which took place in September 
 of the water vapour details shown in the August spectrum. On 
 another occasion Prof. Smyth defended the rainband, Nature, vol. 
 xxix., p. 525, " Rainband spectroscopy attacked again." In an essay 
 read before the Phil. Society of Washington, and printed in the 
 American Journal of Science, the writer of it referred to the " unsatis- 
 factory evidence " of the rainband, because " if the spectroscope is first 
 turned to the sky in any direction, and afterwards to a white wall 
 fifty feet distant, it will be found impossible to distinguish between 
 the appearance of the rainband, as shown by the whole atmosphere, 
 and by the layer fifty feet thick/' 
 
 The Professor disposes of the objection by promptly pointing out 
 that " the white wall reflects the light and sky spectrum solar lines, 
 and telluric lines and all ! " 
 
 Of the books and articles published, the following were kindly 
 sent me by the authors : 
 
 " The Science Monthly," illustrated, for December, 1883. " The 
 Hygro- Spectroscope (or Rainband Spectroscope)," by F. W. Cory, 
 F.R.Met.S., with illustrations of a spectroscope and a rainband 
 spectrum. 
 
 " How to foretell the weather with the pocket spectroscope," F. W. 
 Cory (Chatto and Wiridus, 1884) ; 86 pages, and 10 illustrations of 
 instruments, charts, &c. The Appendix contains the September, 
 1882, Times correspondence in full. 
 
 " Observations of the Rainband from June, 1882, to January 
 1883," by Hugh Robert Mill, B.Sc., communicated by Prof. Tait to 
 the Proceedings of the Royal Society of Edinburgh, with a chart. 
 
 " The Rainband : How to observe it, and what to expect from it," 
 by Hugh Robert Mill. Hilger, 1883. With four figures and a 
 chart. 
 
 In the above papers and volumes are contained much useful in- 
 struction in the use of the spectroscope, and valuable tables and 
 statistics of rainband results, some of which are referred to later on. 
 
 THE INCREASED USE OF THE SPECTROSCOPE. 
 
 The increased use of the spectroscope quickly followed the publi- 
 cation of the " Plea." 
 
 Mr. Browning, at my suggestion, prepared a " standard " instru- 
 
17 
 
 ment (Figs. 2 and 3), in which was represented a spectrum, as nearly 
 like as possible that represented in the frontispiece to the " Plea." 
 
 In this instrument was introduced what I considered for the 
 special purpose an improvement, viz., a fixed slit. This showed ^the 
 lines about as wide as in the plate, and in a series of observations 
 secured their correspondence. 
 
 THE STANDARD SPECTROSCOPE. 
 
 Fig. 
 
 Of course many other opticians soon began to supply "rainband 
 spectroscopes," but these varied considerably in power and disper- 
 sion, and thus did not realize what was my idea of uniformity of 
 observation. I do not wish to specially recommend any maker, but 
 I think it really would be of great advantage if the Royal Meteoro- 
 logical Society or some other competent tribunal would define the 
 width of slit, dispersion of prisms, and the magnifying power to be 
 used. Every observer who has tried several spectroscopes knows 
 how the appearance of the rainband varies according to these 
 incidents. 
 
 One important requirement not yet fulfilled is a gauge or micro- 
 meter to estimate the tint and width of the rainband or bands. The 
 width may be measured (though with difficulty in small instruments) 
 by some form of moving web or point, but a comparison spectrum 
 for tint is far more difficult to obtain. Mr. Mill made to me a very 
 ingenious suggestion of the use of didymium for this purpose. This 
 gives as a salt in solution, or as a component of glass, an absorption 
 band, varying in tint with the thickness of the quantity of the solution 
 or of the glass, and he proposed to use a sliding wedge-shaped cell or 
 plate, and to adjust this till it accorded with the rainband. 
 
 Unfortunately the didymium band falls exactly in the place of a 
 rather strong low sun band, on the more refrangible side of D, and 
 is complicated by it. I propose to avoid this inconvenience by means 
 of a reflecting prism so arranged that the light to pass through the 
 didymium solution or glass shall come from the zenith. For micro- 
 
18 
 
 metric measurement of the band width, and for comparing the didy- 
 mium or any other selected band with the rainband, I know of no 
 better arrangement than one illustrated below (fig. 4). In this case 
 the slit plate is divided horizontally in two, and the upper half with 
 its spectrum is made by means of a micrometer screw to traverse the 
 lower half as shown in the diagram (fig. 5). 
 
 By this means measurements and comparisons may be easily made, 
 e.g., the D lines in the upper spectrum may be used to measure the 
 width of the rainband in the lower, or the didymium band in the upper 
 may be brought into direct comparison with the rainband. The D 
 line or any other may also be brought over and compared with F or 
 other of the solar lines. All these comparisons are thus rendered 
 less difficult than when the bands and lines are a distance apart. 
 
 It has been proposed to place a " condensing lens " in front of the 
 slit, but I do not for ordinary use see any advantage in it. The sky 
 light cannot be condensed, and I doubt whether in any picture 
 
 Fig. 4 
 
 formed on the slit of a small spectroscope it would be possible to dis- 
 tinguish a cloud spectrum from that of the sky. 
 
 In the case of larger spectroscopes, with considerable slit length, 
 the device might perhaps be more useful. 
 
 OBSERVATIONS AND THEIR RESULTS. 
 
 As the number of observers, evidenced by the sale of instruments 
 has increased, so also have the methods, quantity, and quality of 
 the observations. 
 
 With regard to the methods, the more simple form of observation 
 recommended by me in the ' ; Plea " has been by some extended, and 
 
19 
 
 the lesser rainbands, the dry air bands, and the atmospheric linos 
 other than D have all been enlisted into service. By the varying 
 thickness and appearance of these, the judgment obtained from the 
 larger rainband near D has been reinformed and strengthened. 
 
 Much information on this head will be found in Mr. Cory's " How 
 to foretell." 
 
 That observer, too, has extended his scale from Prof. Piazzi 
 Smyth's 10 to 20. After much experience, I still think the scale 
 given in the " Plea," to 5, is the more useful for general observers, 
 except that I have introduced 0--1 as indicating a very faint band. 
 Mr. Cory says " the rainband is never absent." This may be strictly 
 true, but it is more convenient in practice to begin with as indi- 
 cating all that is seen in dry fine weather. 
 
 Mr. J. A. Bramley Moore in a letter to Knowledge, No. 60, p. 485, 
 remarks : " (2) If the sun lines in the green instead of appearing 
 clear and distinct are thick and muddy, heavy rain (like thunder 
 rain) will follow, and this whether there is any " rainband " in the 
 red or not. 
 
 " (3). If on moving the spectroscope slightly to the left the "blue " 
 appears very light, and the dark line down is clearly seen, then wind 
 may be expected." He adds that this " never fails." 
 
 "(4) On one occasion on moving the spectroscope as above, the 
 green instead of giving way to the blue, seemed to fight with it, and 
 pass over it. A thunderstorm followed." 
 
 Twice since he found the same thing to occur. Mr. Cory, p. 30, 
 corroborates this form of thunderstorm prediction. 
 
 Mr. Cory also notices that the rainband decreases before snow, and 
 the diagram on his Plate III. illustrates this. 
 
 He also recommends pointing the spectroscope to the direction 
 from which the wind comes ; a useful suggestion. 
 
 Coming now to the question of how far the spectroscope makes 
 good its predictions, we have : 
 
 (1) General evidence as afforded by the statements of Prof. Piazzi 
 Smyth, Mr. Cory, Mr. Mill, Mr. Clapham, and others, who have 
 borne testimony in favour of its value for forecasting. 
 
 (2). Recorded sets of observations, either daily or as averages for 
 longer periods ; and either in figures, or as lines and curves, express- 
 ing the result in a graphical form. 
 
 In a letter to the Times of September, 23, 1882, Prof. Piazzi 
 Smyth gives a fortnight's notes, September 1st to 15th, 1882, in three 
 columns (1) Temperature, (2) Rainband intensity, (3) Rainfall at 
 the Royal Observatory, Edinburgh. A glance at these will show how 
 rain fell as the rainband increased, and how some small successive 
 rainbands led up to a fall of rain. 
 
 Mr. Cory has not given statistics in his book, but in a letter to the 
 Times, February 1st, 1881, he gives a list of observations taken at 
 9.15 a.m. daily for the month of January of that year. The results 
 are as follows : 
 
20 
 
 1 case of 70% raiiiband was followed by heavy rain. 
 
 2 cases of 60% rain in both. 
 
 8 50% rain every time. 
 
 7 40% rain in 5, overcast in 2 
 
 cases. 
 
 9 30% 6 of rain. 
 
 1 case of 40% decreasing to 30% was followed by nimbus. 
 1 30% increasing to 40% rain. 
 1 20% 30% slight rain and 
 
 heavy snowfall. 
 1 20% was followed by very fine weather. 
 
 31 days. 
 
 These figures seem to be conclusive as to the rainband's predictive 
 value. 
 
 To Mr. Cory I am also indebted for the graphical chart, a copy of 
 which I give on Plate II., showing the mean per-centage of rainband 
 in dotted curves, and the amount of rainfall in vertical lines for each 
 month during the year 1882 and a part of 1883, at Buckhurst Hill, 
 Essex. The observations were taken in the N. direction, three times 
 a day, and at an angle of from 10 to 20 degrees above the horizon. 
 As Mr. Cory remarks in his accompanying letter to me, " there is a 
 decided connection between the two." The high per-centage of rain- 
 band in June and July, with a not excessive fall, is due to the 
 rainband being stronger in summer. The heavy fall in the later half 
 of October was preceded by a very high mean rainband during the 
 first half of the month. Of the fall in March, with a low rainband, 
 half was snow, and the actual amount of rain was very small. 
 
 These apparent discrepancies are consistent with the rainband laAvs. 
 
 Mr. Mill, in his u The Rainband," gives a graphical chart and some 
 tabular statements showing how his rainband predictions were ful- 
 filled. 
 
 Tables II., III. and IV. in that work give the results when the 
 rainband was compared in intensity with the Fraunhofer lines, 
 b and F, during seven months of 1882. 
 
 These tables show there was 8 per cent, of cases when the rain did 
 not, and 92 per cent, of cases when the rain did, follow maximum 
 rainband; and 21 per cent, of cases when the rain did, and. 79 per 
 cent, of cases when the rain did not follow a minimum rainband. 
 
 Table V. gives the result of observations made in Callander for 
 the months June to December, 1882 : 
 
 Rain predicted ... ... ... ... ... 125 
 
 Rain followed 97 
 
 Per-centage of fulfilled predictions .. 78 
 
PLATE II. 
 
 MONTHLY RAINFALL AND RAINBAND, 1882-3. 
 
X. 
 
21 
 
 No rain predicted... ... ... ... ... 80 
 
 No rain followed 51 
 
 Per-centage of fulfilled prediction 
 
 64 
 
 Total predictions 205 
 
 Total fulfilments 148 
 
 Per-centage of total fulfilled predictions ... = 72 
 
 Table VI., for January to September, 1883, gives the total of ful- 
 filled predictions at 209, and of unfulfilled 64. Per-centage of ful- 
 filled predictions = 76 - 5. 
 
 With respect to the Guildown observations, these have been taken 
 since the 1st of July, 1880, at 9 a.m. daily, with the spectroscope, 
 and in the manner mentioned in the " Plea." All the barometric 
 and other meteorological observations for a half year are from time 
 to time reduced to curves upon a chart, in which, in tenths of inches, 
 the days of the year form the abcissce, while the readings of each 
 instrument form the ordinates. In these the rain is shown in tenths 
 of inches of fall, and the rainband in degrees of strength 1 to 5. 
 
 The rainfall and rainband portion of the chart for four consecutive 
 months of 1881 is shown in Plate III. 
 
 These charts if put together would extend to a length of 12 feet 
 2 inches, and comprise over 1,800 observations. I have not tabu- 
 lated the results except for yearly values, but a glance at the curves 
 ought to convince the most sceptical that the connection between 
 the rainband and rainfall is, as a general rule, well established. 
 
 The yearly values run out thus : 
 
 Table of Yearly Values of Rain and Rainband. 
 
 YEAU. 
 
 Rainfall in 
 inches. 
 
 Rainband in 
 numbers. 
 
 
 1881 
 
 25-68 
 
 353-5 
 
 
 1882 
 
 28-10 
 
 392-5 
 
 1 of Rainband 
 
 1883... 
 
 24 '35 
 
 404-5 
 
 - -Q6 of Rain 
 
 1884 
 
 18-70 
 
 314-0 
 
 
 
 
 
 
 It is obvious that if such a method of long-period comparison as 
 this shows an approximate reciprocal rise and fall in the total values 
 of rain and rainband it is as much as can be expected from it. If 
 special circumstances prevail, such as fogs and mists, which give a 
 low rainband without rain, we may expect to find (as in 1883 and 
 1884) an advance of total rainband over rain for that year. 
 
 Other observers doubtless have preserved records which have not 
 come under my notice ; but taking Mr. Cory's, Mr. Mill's, and the 
 Guildown ones alone, I think the fact is established that the little 
 dark " bar " in the yellow of the spectrum can well hold its own in 
 
forecast with any other " bars," and that its character has been 
 amply vindicated. 
 
 It now only remains to refer to one or two meteorological subjects 
 allied to the rainband, but not generally finding a place with the 
 observations of pressure, temperature, wind, &c. These are ozone, 
 atmospheric electricity, and the weather compass for forecasting 
 invented by the late Prof. Klinkerfues. 
 
 THE RAINBAND AND OZONE. 
 
 Mr. Cory, in his " How to Foretell," (p. 32) remarks that the blue 
 and yellow colours in the spectrum are useful guides to the presence 
 or absence of ozone. If the air is very pure, the blue will be clear, 
 and F will stand out distinctly, while the yellow will show itself as a 
 true colour or have an orange tint. If the reverse, the yellow will 
 have a greenish hue, and the blue will be deep and dark, with an 
 indistinct r. 
 
 I have not particularly observed these colour changes, but the 
 meteorological charts above mentioned contain ozone curves on the 
 same principle as those of the rainband, and for similar periods. The 
 scale for rainband is, as before, 0-1 to 5 ; that for ozone 1 to 10 of 
 Negretti and Zambra's scale for their iodide of starch papers. A por- 
 tion of one of the charts comprising four months (the first of each 
 quarter of 1882) is given in Plate IV. An examination of this will 
 show that generally the curves of rainband and ozone agree in rising 
 and falling together. It does not of ten occur that ozone is nil; but when 
 it is, rainband also is found absent. This is indeed what might have 
 been expected, for with warm winds, W. and S., the rainband is re- 
 inforced ; with cold winds, N. and E., it is depressed. A similar 
 effect, but even more regular in its action, is found with the ozone 
 tests. Thus a S. W. wind gives the strongest tinted papers ; a N.E. wind 
 the lightest. We know so very little of ozone and its properties 
 that it would not be safe to connect its quantity in the air with con- 
 ditions of moisture, though such a connection may be fairly suspected. 
 
 Guildown is remarkable for exceeding in average quantity of 
 ozone places situate much nearer the sea. This is probably due to 
 its altitude of 225 feet, and to an open valley to the W. from which 
 there is a prevalent air current. 
 
 ATMOSPHERIC ELECTRICITY. 
 
 In the "Plea" I suggested that observations of atmospheric elec- 
 tricity might usefully accompany those of rainband. The rela- 
 tion of these to each other becomes more apparent when the influ- 
 ence of electricity upon aqueous particles is considered, and how the 
 size of these latter determine the strength of the rainband. 
 
 When these are minute in the form of transparent water vapour, 
 evidenced only by the hygrometer, the rainband is strong. When 
 the particles are larger in the shape of visible fog or mist, the rain- 
 band considerably weakens. Lastly, when the gross particles fall as 
 heavy rain-drops or snow-flakes, there is frequently no rainband, or 
 
23 
 
 hardly any. Now, the property of atmospheric electricity (as shewn 
 in the familiar experiment of a sponge suspended from the prime 
 conductor of an electrical machine) is, when developed, to cause the 
 finer cloud particles, by mutual repulsion in the first instance, to 
 coalesce and descend as rain. Electric action is always strongly 
 marked when rain suddenly falls, even to the extent of yielding 
 sparks from a properly insulated conducting wire, and it has evidently 
 much to do with the breaking up of clouds. I have not traced, as 
 Mr. Moore and Mr. Cory have, a forecast of storms by the aspect of 
 the rainband, or the colours of the spectrum, but I have noticed a 
 sudden increase of atmospheric electricity, and a weakening of the 
 rainband frequently to accompany a clearing shower. 
 
 Those who desire to combine observations of atmospheric electri- 
 city with those of the rainband, will find the mode and the apparatus 
 used fully described and illustrated in the Metewological Magazine for 
 August and October 1885. 
 
 The collecting is effected by means of elevated points, or a water 
 stream, and the examination by a Bohnenberger suspended gold leaf 
 electrometer ; or by a Thomson's quadrant electrometer, excited by 
 a chloride of silver battery. 
 
 KLINKERFUES' WEATHER COMPASS. 
 
 Lastly, I have to notice an instrument invented by the late Prof. 
 Klinkerfues, of Gottingen, for the purpose of weather forecast. It is 
 an ingenious combination of an aneroid barometer, a string hygro- 
 meter, and a wind scale, jointly affording indications of the effects of 
 pressure, moisture and wind. A general idea of its construction will 
 be obtained from the annexed wood cut (Fi; 6). 
 
 Fig. 6. 
 
24 
 
 In this drawing a is the aneroid vacuum box; b, moveable 
 weather scale ; s, moveable wind scale ; c, hygrometric hair string ; 
 d, segment actuating index; e, lever connecting barometric with 
 hygrometric effects; / and g, arms to which the hair string is 
 attached ; h, lower end of index, the upper end of which projects on 
 to the weather scale. 
 
 The working arrangement is such that in dry air conditions the 
 hygrometer string acts with the barometer for a rise ; and in moist 
 weather against it ; and the two instruments thus comjbine in a joint 
 reading, depending on the variation of each. When fine weather is 
 approaching, the hygrometer will give the barometer an extra " pull 
 up," and in moist assist it in "a fall," while at times the two may 
 balance one another. 
 
 In this way more variation is obtained than with the ordinary 
 barometer, and the concurrent effects of pressure and moisture are 
 read off. 
 
 To forecast, the method is this 
 
 At any definite time, say 9 a.m., set the outer dial with the words 
 describing the weather, " Rain," &c., with the inner wind dial, so that 
 the word denoting the prevailing weather will stand against the wind 
 direction at the time, e.g., set the centre of the larger dial " Change " 
 against the centre of the wind dial " North ; " then turn both dials 
 together, until the index covers the words "Change " and " North." 
 Twelve hours after, we will suppose the index to have risen to 
 " Fair/' and the wind to have changed to the " West." We must now 
 move the outer dial only in the wind direction, so as to correspond with 
 the pointer " West." 
 
 This will bring " Change " again under the index, and indicate that 
 the prospect of fair weather shown by the index rise has been 
 neutralized by the wind change, and changeable weather may conse- 
 quently be predicted. Had the wind gone Eastward with the index 
 rise, the words " Set Fair " would have taken the place of " Fair," and 
 continuous fine weather would have been foretold. Of course no 
 meteorological instrument is infallible ; but I may fairly say that 
 with proper care in setting, much may be made of the " Klinkerfues " 
 for weather forecasting. A friend of mine, a large farmer, has used 
 one for years ; and to quote his own words, " I always set my farm 
 work by it." 
 
 To prevent disappointment in its use, it is necessary to remember : 
 
 1. That its movements are relative, and are not intended to com- 
 pare with those of the barometer, being on nearly twice the scale, 
 and acted upon hygrometrically. 
 
 2. It must be set each time as before described for a forecast. If 
 left alone with " Change " at top, the index will sometimes run right 
 off the marked part of the dial, in consequence of the greater range. 
 
 When sent from abroad by the patentees (Messrs. Biernatzki & Co., 
 of Hamburg), the index is secured to ensure safe travelling. This 
 has to be released, and then set by a screw at the back of the case, 
 either by a barometer, or to the prevailing weather sign. This 
 
25 
 
 setting should not afterwards be altered, the dials being in future 
 adjusted to the index, and not it to them. 
 
 How sensitive the hygrometric action is, may be seen by breathing 
 on the back of the case, when the index will at once be in movement. 
 
 The instrument, although now introduced some years, has not been 
 so well received as it deserves, owing, as correspondents have told 
 me, to the setting arrangement not being properly understood. It 
 is, however, after a little practice, very simple. Though not in 
 strictness an instrument fully adapted to scientific research (a divided 
 scale would add to its value), it certainly merits attention, if it will 
 only succeed in saving a hay crop, or telling the farmer how long his 
 stacks may remain out, matters as to which his mercurial barometer 
 sometimes misleads him. Probably a better acquaintance with it by 
 meteorologists would more fully develope its qualities as an adjunct 
 to the rainband spectroscope, for which it seems well adapted. 
 
26 
 
 APPENDIX. 
 
 ATMOSPHERIC ELECTRICITY. 
 
 To the Editor of the Meteorological Magazine. 
 
 SIR, Noticing a reference in your current number to the subject 
 of atmospheric electricity, it occurred to me that you might be 
 interested to know of some experiments in that regard which have 
 been tried here. The collecting sources are two 
 
 (1) A long cane carrying a brass ferule armed with three fine 
 
 platinum points, elevated some 30 feet above the ground, 
 on a building situated near the Observatory. 
 
 (2) A tower situated on a rounded eminence, 620 ft. to the N. 
 
 of the Observatory, its base being 55 ft. above it. 
 
 The conducting wires are of copper, gutta percha covered, and are 
 led into the Observatory. The cane on the building is insulated, by 
 being divided by a vulcanite stem protected by a copper funnel, the 
 wire passing inside the upper half. 
 
 The pole on the tower terminates in a corona of 25 platinum 
 points, and this is insulated by being placed on a glass rod, which 
 runs through a Mascart bottle filled with sulphuric acid. The corona 
 
 I is about 30 ft. above the base of the tower. 
 The receiving apparatus is of three sorts 
 
 Fig. 7. 
 
27 
 
 (a) A Bohnenberger electrometer composed of a single gold leaf 
 
 suspended between the opposite poles of two Zamboni's 
 piles. 
 
 (b) A pith ball electrometer, consisting of two gilded pith balls 
 
 suspended in contact by fine platinum wires. 
 
 (c) A Thomson quadrant electrometer of simple form, in which 
 
 the ordinary arrangement is reversed, the needle being 
 used to test the wire, while the opposite pairs of quadrants 
 are kept permanently charged by two of De La Rue's 
 chloride of silver batteries of 30 cells each, connected at 
 centre to earth (Figs. 7 and 8). 
 
 The needle carries a mirror, and the deflections are read off on a 
 scale in the usual way. The instruments are usually examined at 
 9 a.m. , and specially as occasion offers. 
 
 The Bohnenberger is the most sensitive, and is affected by small 
 currents. The pith balls are used as these are found stronger. The 
 quadrant is employed for measurement of quantity and duration of 
 current. Generally the lower points are found to give stronger 
 indications than those on the Tower, which I attribute to the greater 
 resistance in the longer length of wire. 
 
 In calm weather the electricity is usually feeble and Positive. In 
 broken weather Negative electricity is oftener developed ; but some- 
 times the sign changes rapidly. On one occasion at least I have 
 found the upper and lower points of opposite signs simultaneously. 
 As a shower of rain or hail comes on, the current strengthens, and 
 sparks now and then fly from the wires. Once my assistant obtained 
 long ones from the wire, and rapid discharges from a pint Leyden 
 jar, coupled up to it. The quadrant arrangement seems a useful 
 one, as avoiding the need of a " replenisher," and as affording a con- 
 stant charge ; and I have every reason to be satisfied with it. 
 
 I have not at present examined and arranged the results obtained 
 since the apparatus has been at work, but I hope to do this shortly 
 in connection with the general meteorological observations taken at 
 the same time. We seldom get heavy storms, as they are apparently 
 broken up by the Hogs' Back and opposite hills ; and cases of light- 
 ning injury are rare. I have not yet tried a small captive balloon, 
 but probably valuable results might be had by thus extending the 
 exploring height. The observatory (51 13' 39 "'2 N. ; 028'47"W.) 
 faces south on the spur of the Hogs' Back, and is 150 feet above 
 Guildford town, and 250 feet super mare. Booker's Tower is marked 
 on Ordnance Map, B M. 305 ft. 5 in. 
 
 J. RAND C APRON. 
 
 Guildown Observatory, July 18th, 1885. 
 
28 
 ATMOSPHERIC ELECTRICITY. 
 
 To the Editor of the Meteorological Magazine. 
 
 SIR, In continuation of my former letter, and before stating the 
 " results," I wish to describe another way of collecting electricity 
 from the air which has been adopted. This consists of a copper can 
 about six inches across and eighteen inches high, and containing 
 about two gallons of water. This is furnished with a long tube or 
 spout, ending in a brass tap with a small aperture. It is placed on a 
 Mascart insulating stand, and connected with the electrometers by a 
 copper wire. As soon as the tap is turned on, and the water issues 
 from it, the can at once becomes charged with electricity of the same 
 sign as the surrounding air. The effect is greatest when the stream is 
 broken into drops in its fall. This apparatus (Fig. 9) was found to 
 give, at 15 ft. above ground, deflections of 5 and 10 with the quad- 
 rant electrometer, when both sets of points gave no signs of charge 
 whatever. At another time, and when only 4 ft. from the ground, it 
 afforded results, the air being so damp that it was difficult to excite 
 the electrophorus, with which the quadrants were at that time 
 charged. It is thus very sensitive, and at the same time portable. 
 
 The general observations have been hardly numerous enough to 
 warrant the assertion of fixed laws, but they seem to establish the 
 following facts pretty satisfactorily : 
 
29 
 
 (1) The wind is evidently a strong excitant of electricity. One 
 
 bright morning, as gusts of wind swept across an outside 
 insulated brass plate, each gust was accurately repeated 
 by a beat of the gold leaf suspended in the Bohnenberger 
 electrometer. 
 
 (2) As a rule, though not without exception, the mornings 
 
 marked " blue sky " showed feeble positive electricity. 
 The exceptions seemed to have occurred lately, when 
 much morning mist has prevailed, and the hygrometer 
 has stood high. 
 
 (3) Clouded and damp mornings, though also with exceptions, 
 
 have yielded the negative sign. 
 
 (4) Storms (with one exception) have always given a strong 
 
 negative sign as they approached the "points." As 
 snow or rain fell, this changed to positive, and in 
 several instances there was a change back to negative 
 before the indications ceased. The exception was a 
 storm on the 24th of July, 1884, at 8.30 p.m., after a 
 fine day, when the sign was first positive, then negative, 
 and ultimately positive again. On rain or snow falling, 
 the electrical conditions in these cases, became very 
 marked, sparks flying from the ends of the conducting 
 wires, the pith balls diverging widely, the mirror deflec- 
 tions amounting to 80, and the gold leaf being torn 
 away or broken up. 
 
 (5). Probably strata opposite in sign may co-exist at different 
 elevations above the earth's surface. Thus on December 
 6th, 1883, at 10 a.m., a snow-storm coming on, the 
 tower points were strongly negative, but the points near 
 the observatory were charged positively, and this per- 
 sisted for a quarter of an hour. 
 
 (6). The observations do not show with any certainty whether 
 the quantity of electricity varies with the height of the 
 points above the observatory. Five instances are, how- 
 ever, marked "from the tower only," and two "from the 
 lower points only." The tower current has at times 
 been the stronger. Generally it is the weakest, but this 
 I attribute to the resistance of 300 feet of wire, which 
 complete its connection with the receiving apparatus. 
 
 From what I have described, it will be seen that periodic observa- 
 tions of atmospheric electricity are possible with simple and inexpen- 
 sive apparatus. Where expense is not an object, it would be easy to 
 convert these into self-recording forms (as at Greenwich), and thus 
 obtain a continuous and more valuable series of observations. 
 
 J. BAND CAPRON. 
 
 Quildown Observatory, August 9th, 1885, 
 
30 
 
 INDEX. 
 
 PAGE 
 
 Abercrombie, R., Rainband and 
 
 Isobars 15 
 
 Agricultor on Rainband 15 
 
 Angstrom, Prof , Solar Spectroscopy 5 
 
 Argyll, Duke of, on Rainband 15 
 
 Atmospheric Electricity (appendix).. 26 
 ,, Apparatus for Collecting and 
 
 Testing 26 
 
 and Rainband 13, 22 
 
 Results at Guildown 29 
 
 ,, and Rainband Spectra de- 
 scribed 7 
 
 Beckett, Sir E., on Official Forecasts 15 
 
 Collecting Apparatus of Atmospheric 
 
 Electricity described 8 
 
 Cory, F. W. , " How to Foretell "... 16 
 Monthly Rainfall and Rainband 20 
 ,, Percentage Result of Predic- 
 tions 20 
 
 Diagrams, Rainfall and Rainband, 
 
 described 9, 21 
 
 Diagram, Rainbaud and Ozone, de- 
 scribed 22 
 
 Electrometer and Battery for observ- 
 ing Atmospheric Electricity, de- 
 scribed 27 
 
 Fogs and Mists, Effect of on Spec- 
 trum 10, 13 
 
 Gladstone, G., Research on Atmo- 
 spheric Spectrum 15 
 
 Guildown, Result of Observations at: 
 
 for Atmospheric Electricity 29 
 
 ,, for Ozone 22 
 
 ,, for Rainband 21 
 
 Klinkerfues Weather Compass de- 
 scribed 23 
 
 ,, Forecast by 24 
 
 Micrometer Slit Plate described 18 
 
 Mill, H. R., Per-centage result of 
 
 Predictions 20 
 
 "The Rainband" 16 
 
 ,, Use of Didymium Wedge 17 
 
 Moore, Bramley, J. A. , Observations 
 
 on Spectrum 19 
 
 PAGE 
 Ozone, Effect of Cold Winds on ...7, 22 
 
 Effect on Spectrum 22 
 
 And Rainband 13, 22 
 
 ,, And Rainband Compared 22 
 
 Predictions by^Rainband 8, 
 
 12 
 
 Rain, effect on Spectrum 8, 12 
 
 Rainband and Atmospheric Elec- 
 tricity 22 
 
 Description of 5 
 
 ,, History of 5 
 
 ,, Literature (recent) of 14 
 
 ,, Mode of observing 6, 11 
 
 Monthly, and Rainfall (Cory).. 20 
 ,, Observations and their Re- 
 sults 12, 18 
 
 and Ozone 13, 22 
 
 Predictions by 8, 12 
 
 and Rainfall, Guildown, 1880 
 
 and 1881 9, 11 
 
 and Rainfall, Guildown, 1881 11 , 21 
 
 ,, Rules of conduct of 12 
 
 ,, Scale of Degrees 7, 19 
 
 ,, Spectra (see Frontispiece) de- 
 scribed 7 
 
 ,, Spectroscope for Observing re- 
 quired 6, 17 
 
 ,, Strong, instances of 5,11, 12 
 
 ,, Yearly Results at Guildown ... 21 
 
 Smyth, Prof. Piazzi, Researches in 
 
 Rainband Spectroscopy ...5,12, 14 
 
 Snow, Effect on Rainband 10, 19 
 
 Spectra Atmospheric and Rainband 
 
 described 7 
 
 Spectrum, double, described 18 
 
 Spectroscope, Early Application of... 5 
 
 Early Figure of 15 
 
 ,, Increased use of 16 
 
 ,, Micrometer slit plate described 18 
 
 ,, Rainband described 6 
 
 Standard 17 
 
 Thunderstorm, Predictions of 19 
 
 Weather, Forecast by Klinkerfues 
 
 Compass 24 
 
 Winds, Cold, Effect of on Spectrum.. 
 
 7, 13 
 
 G. SHIELD, PRINTER, SLOANE SQUARE, S,W. 
 
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