S. Department of Boriculture,
WEATHER BUREAU.
INSTRUCTIONS
FOR
VOLUNTARY OBSERVERS
PREPARED UNDER DIRECTION OF THE CHIEF OF THE
WEATHER BUREAU.
T. RUSSELL,
PBOFESSOB OF
PUBLISHED BY AUTHORITY OF THE SECRETARY OF AGRWULTU&S.
WASHINGTON, D. C.:
GOVERNMENT PRINTING OFFICE.
1892.
ZIU S. Department ot Bgriculture,
WEATHER BUREAU.
INSTRUCTIONS
FOR
VOLUNTARY OBSERVERS
PREPARED UNDER DIRECTION OF THE CHIEF OF THE
M ^ . WEATHER BUREAU.
BY T. RUSSELL,
PBOFESSOB or METEOROLOGY.
PUBLISHED BY AUTHORITY OF THE SECRETARY OF AGRICULTURE.
WASHINGTON, D. C.:
GOVERNMENT PRINTING OFFICE
1892.
GIFT
. .:*.; : :
TABLE OF CONTENTS.
Page.
Introduction 9
Voluntary observer's form of application 11
Thermometers i 12
Minimum thermometers 15
Maximum thermometers 18
Instructions for setting up maximum thermometers 20
Instructions for setting up minimum thermometers 20
Thermometer shelter 22
Window or wall shelter J - 23
Daily mean temperature 24
Solar radiation thermometer 25
Thermoscope 26
Water vapor in air 27
Psychrometer 28
Sling psychrometer 29
Hair hygrometer 30
Barometer , 30
Vernier 33
Correction of barometric observations 38
Aneroid barometer 41
Hypsometer 42
Rain gauge 43
Instructions for use of rain gauge 44
Rain gauge support 46
Percolation gauge 49
Wind vane 50
Anemometer - 51
Clouds 55
Evaporation ..." 57
River gauge 58
State of weather 60
Frost - 60
Coronas 60
Thunderstorms 61
Tornadoes and Sand spouts 61
Instructions for observing Auroras 61
Earthquakes 64
General phenomena of Climate 66
Special instructions to voluntary observers 67
Instructions in the use of the tables 69
Table I. Temperature of the dew point 71
II. Relative humidity, per cent 81
III. Correction of vapor pressure 91
IV. Vapor pressure in inches 92
V. Grains of water-vapor in a cubic foot of air 93
VI. Reduction of barometer readings to 32 94
VII. Reduction of observations of barometer to sea level 96
795 8
LIST OF ILLUSTRATIONS.
Page.
Figure 1. Maximum and minimum thermometers 19
2. Design for thermometer shelter 22
3. Solar radiation thermometer 25
4. Alcohol radiation thermometer 25
5. Mounting of barometer 31
6. Vernier 35
7. Vernier 35
8. Vernier 35
9. Barometer cistern and scale 37
10. Barometer cistern section 37
11. Aneroid barometer 41
12. Eain gauge, front view 45
13. Kain gauge, vertical section 45
14. Rain gauge receiver 45
15. Rain gauge receiver, horizontal section 45
16. Rain gauge and support 46
17. Wind vane 50
18. Anemometer 51
19. Anemometer dial 54
20. Piche evaporometer 58
21. River gauge 59
7
INSTRUCTIONS TO VOLUNTARY OBSERVERS OF THE WEATHER
BUREAU.
INTRODUCTION.
To render the meteorological observations made over the United
States of the greatest value, and for ease and facility in their use in
the investigation of questions relating to the weather, it is important
that they be made on a uniform plan and the records kept on some
uniform system.
With a view to accomplishing this, a general description is here
given of the best methods of making meteorological observations
and the instruments used for the purpose. This is prepared specially
for the information of the voluntary observers of the United States
Weather Bureau under the Department of Agriculture.
Observations have a two-fold object : First, to obtain a knowledge
of the climate of a region, that is, the average of the .various air-
conditions over a country that affect the convenience, comfort, or
health of the people, or influence plant growth ; second, the dis-
covery and improvement of rules and methods for making weather
predictions. For this purpose the observations over an extensive
area of country are used to trace the origin, direction, and rate of
progress of pressure and temperature changes in the air, the occur-
rence of rainfall, and the direction and velocity of wind as dependent
on the variety in distribution of pressure and temperature over a
region.
The successful predictions of the principal weather changes, such
as cold waves, storm winds, heavy rainfalls, and great river floods,
are of the highest practical value to people. The attainment of this
important object, even with only a partial degree of success, is a
sufficient motive for the labor bestowed in making and preserving
the vast amount of weather observations now going on in most
countries all over the world.
Observations are desired in at least one place in every county of
every State in the United States. For the purpose of procuring
these observations the Chief of the Weather Bureau is authorized by
law to loan instruments to observers desirous of making the observa-
tions, but on certain conditions. These conditions are the safe keep-
ing and return of instruments, and that a copy of the observations
be furnished to the Weather Bureau Office, Department of Agri-
culture, at Washington, D. C., free of expense to the United States
Government.
9
i fc - 10
G'f fimiry"' precautions "'arfe required in the use of instruments.
Observers are not, however, held responsible for the breakage or loss
of instruments due to unavoidable accidents incident to their use in
the making of observations.
The observations in which the Weather Bureau is most interested
are rainfall and temperature. Thermometers and rain-gauges are
furnished to the observers free of any charges for instruments or
for transportation to the observers.
Blank forms and franked envelopes are furnished to the observers
for transmission of reports to Washington, D. C., free of expense to
the observer. Observers ajre also furnished free with a copy of the
Monthly Weather Review, an official publication which gives a sum-
mary of the weather all over the United States for each month, the
mean temperatures and total rainfalls for places, descriptions of
progress of principal storms, cold waves, and floods during the
month, etc.
Voluntary observers are not furnished with barometers, wind-
vanes, or anemometers. Many of the observers have these instru-
ments, their own private property, and instructions are, therefore,
here given regarding their use and care.
Observations of air pressure and wind velocity by voluntary ob-
servers are not desired by the Weather Bureau. Enough data of
this nature for the purposes of the Bureau, the forecasting of weather,
are obtained from the regular meteorological stations. Observa-
tions of pressure by voluntary observers are mainly of interest to
the observers themselves at the time of the observation in esti-
mating the location of storm centers in vicinity where there is no
access to the daily weather map issued by the Weather Bureau. The
detailed or average values of pressures are of little value for climate.
The rainfall and temperature observations are intended to be used
in the Weather Bureau in working up the climatology of the whole
country.
A trustworthy record of the weather is always of interest to any
community, and is often of very great practical value. It is one of
the objects of the Weather Bureau to foster and encourage the keep-
ing of such records. There are numerous calls for records of the
weather as evidence in courts in important law cases months, and
even years, after the record is made. Contractors and others inter-
ested in outside work often want a record of days when there was
rain or high winds, when streams were frozen over or swollen with
floods, etc. Farmers are interested in the state of the season,
whether forward or backward, as regards temperature and rainfall.
A double supply of blank forms is furnished observers in order that
a copy of the weather record may be retained for their own use.
A person desiring to become a voluntary observer is requested to
fill out a form (No. 4006), a specimen of which is shown below.
11
[FORM No. 4006 Mis.]
APPLICATION FOR METEOROLOGICAL INSTRUMENTS.
I, , County of , and State of , do hereby request to be
furnished with one maximum thermometer, one minimum thermometer, and one
standard rain-gauge, with the necessary supports, for use in making daily observa-
tions of temperature and precipitation, and Thereby agree to send a monthly report of
such observations on Form No. 1008, Meteorological blanks and penalty envelopes to be
furnished by the Weather Bureau to the Observer, Weather Bureau, .
I do further agree to RETURN all of said instruments to the Observer, Weather
Bureau, , or to turn them over to a duly appointed successor, whenever,
from any cause, except sickness or unavoidable absence from home, I fail to make the
observations hereinbefore agreed upon.
I further agree to exercise a reasonable degree of care in handling the above-
named instruments, to care for them as I would my own property, and to return those
which may be accidentally broken or otherwise become unserviceable, with a state-
ment covering the circumstances which caused the damage.
(Signature)
I,- , postmaster of , do hereby certify that , who
signs the above application, is personally well known to me, and I fully believe him
to be a responsible person, and that he will faithfully perform the obligations assumed
by him in his application.
(Signature)
Postmaster.
(Date) , 189 .
U. S. DEPARTMENT OF AGRICULTURE,
WEATHER BUREAU,
(STATION)
Issued maximum thermometer No. , minimum thermometer No. , rain-
gauge No. ,and notified the central office.
Observer, Weather Bureau.
(Date) , 189 .
The observer is accepted if there is not already one in the vicinity.
A list of the various observers and their location is published every
three months in the Weather Review.
Voluntary observers receive no pay for services.
. METEOROLOGICAL INSTRUMENTS.
The most important conditions of the air, the subject of inves-
tigation, and the instruments used in observing them are as follows:
Temperature observed by means of thermometers.
Water- vapor pressure in air, measured with dew-point apparatus or psychrometer.
Pressure, observed with mercurial barometer, aneroid barometer, and hypsometer.
Rainfall, measured with rain-gauge.
Rainfall, reaching different depths in the earth, measured with a percolation
gauge or lysimeter.
Snowfall, melted, measured with a rain-gauge.
Wind direction, observed by a wind vane.
Wind velocity, measured by an anemometer.
Clond motion, observed with nephoscope.
Cloudiness, amount in fractional part of the sky covered, estimated with the eye.
Sunshine duration, measured with a sunshine recorder.
Electrical potential, measured with an electrometer.
Evaporation, measured with evaporometer.
Fog, haze, estimated.
12
In river observations the important conditions are:
River stages, the vertical height in feet of river surface above low water,
observed on a river-gauge.
River-current velocity, measured with a current-meter or ship's log.
THERMOMETERS.
The most important condition of the air is temperature. A mer-
curial thermometer used in observing- temperature consists of a glass
bulb and stem containing mercury. Substances expand slightly with
heat. Mercury expands seven times as much as glass. The height
of the top of column of mercury in the stem is a measure of the
temperature. The thermometer takes the temperature of the air by
the contact of particles of air with the bulb.
The best forms of thermometers have the graduations etched on
the glass-stem of the instrument.
On the Fahrenheit scale, the only scale in use in meteorological
observations in the United States, the temperature of the melting
point of ice is taken as 32, usually called freezing point, and the
temperature of boiling water under a standard pressure of the air
of 29.922 inches, as 212, usually called boiling point.
The temperature of melting ice varies slightly with the pressure
of the air. Doubling the pressure of the atmosphere lowers the
temperature 0.0135 ot a degree. This must be distinguished from
the effect of an additional pressure of an atmosphere on the bulb of
a thermometer. For an ordinary thermometer the increase of pres-
sure on the bulb for one atmosphere compresses the bulb to such an
extent that the column of mercury in the stem will stand 0.5 of a
degree higher than without the pressure.
When a thermometer is made, the stem is closed with the mercury
near the top, so that it contains very little air. When the top of the
stem is broken, admitting the pressure of the outside air, the reading
is lowered about 0.5 of a degree.
At boiling point, doubling the pressure of the air raises the boiling
point to 250.
The volume of the stem from 32 to 212 is divided into one-
hundred and eighty equal parts by the graduations of the scale.
The temperature corresponds to the graduation the mercury reaches
on stem numbering the degrees consecutively from 32 up, and
numbering down consecutively below 32.
The indications of a mercurial thermometer are trustworthy as
low down as temperatures on the very verge of the melting point of
frozen mercury, 37-9. Mercury vaporizes at a temperature of
6 42 .6.
For very accurate temperatures several requirements are neces-
sary. The thermometer used in taking the temperature should be
compared with a standard thermometer by comparative readings of
13
the two instruments at different points along the scale in water kept
thoroughly stirred. For points below 32 the comparisons have to
be made in a bath of alcohol. In this way a list of corrections of
the thermometer is made, which are to be applied to any readings
made in order to obtain the true temperature.
The following is a specimen:
SCALE READING.
CORREOTIO:
-28
-f 1.0
-18
+ 0. 4
8
-0. 2
4 2
0. 6
12
1.1
22
0. 6
32
0. 4
42
-0. 3
52
-0. 1
62
+ 0. 1
72
+ 0. 3
82
+ 0. 5
92
+ 0. 8
102
-fl. 1
The correction should be applied algebraically to the scale read-
ing of the thermometer. For a temperature not given in the list
of scale readings, an interpolated value of the correction is used.
For the reading of 67.5 for instance, the correction is + - 2 and
the true temperature 670.7; for 22 the correction is 0.6 and the
true temperature 21. 4.
Caution is required in applying the correction to a minus scale
reading when the temperature is below zero. For the reading of
28.o, for instance, the correction is + i.o; the true temperature is
28.0 4- i.o = 27.0. In applying the correction, like signs add,
dissimilar signs subtract.
There is a constant rise in the freezing point of a thermometer
with age, due to a slow and steady contraction of the glass bulb. A
thermometer graduated the day it is filled will read a degree and a
half higher a week after. Good thermometers are not graduated
until a year or two after filling. In the course of three years the
freezing point will rise a half degree. This varies very much in
different instruments, depending on the nature of the glass. Some
varieties of glass are now used in making thermometers that vary
very little with age.
Any change in the freezing point of a thermometer changes the
whole series of corrections throughout the scale correspondingly.
In the case of the thermometer above, if the correction at freezing
point is found on packing the instrument in melting ice at some
future time to be 0.9 of a degree instead of 0.6; that is, if its
reading in ice is 320.9 instead of 320.6 as would be the case now, then
there is a change of 0.3 of a degree throughout the scale, the instru-
14
ment reading that much higher at every point. The correction at
62 instead of being o.i will be 0.4 at 72, instead of -f o.i; it
will be 0.2, etc.
After a thermometer has been heated to a very high temperature,
as the boiling point, there is a depression of the freezing point of
about 0.4 of a degree, which is fully recovered in six weeks. Sub-
jecting a thermometer to a very high temperature, as 500, raises the
freezing point permanently from 10 to 1 8. Long exposure to a low
temperature as 30 will raise the freezing point about o.i of a
degree.
The valid freezing point correction to be used in correcting the
indications of a thermometer to the true temperature is the freezing
point correction observed just after exposure of the thermometer to
the temperature. Ordinarily for such range as there is in the
temperature of the air the freezing point observed once a year gives
the correction with sufficient accuracy to o.i of a degree.
Thermometers are made with cylindrical and spherical bulbs.
The cylindrical form is the most popular at the present time. It is
usually more sensitive than a spherical bulb, as it exposes more
surface to the air for the same quantity of mercury contained.
Spherical bulbs can, however, be blown thinner than cylindrical
ones, and the glass is commonly more uniform in thickness.
In observations of rapid change of temperature, as in a balloon
ascent, a thermometer has to be very sensitive to give a correct
result. In fact a correction has to be applied where accuracy is
required. A thermometer may sometimes be found in error from a
break in the column of mercury or from a bubble of air in the bulb.
A thermometer to be in the best condition ought not to have its
column broken when held with the bulb uppermost. To remove
the air the speck in the bulb should be first brought to the junction
of the stem and bulb by jarring the latter in the open palm of the
hand. When the speck is at the junction, prepare ice or snow or
cold water and cool the bulb down, then invert it, and all the mercury
will run to the other end, or may be made to do so by a gentle jar,
Now heat the bulb, either in the hand or at a long distance from a
heated surface, being careful to hold the stem horizontal or inclined,
with the bulb end up. This will cause the mercury to rise and drive
the air before it. Care should be taken never to heat so much that
the top of the column is less than a half-inch from the end of the
other detached column, as otherwise the thermometer may be broken.
If, now, the thermometer is held vertically the two columns will join,
or may be made to do so by a gentle jar in the open palm of the hand;
the air speck will be in the tube, but the mercury will join by a
slender thread alongside of the speck. Now, if the bulb be cooled,
the air-speck will remain stationary, but the mercury will flow past
it toward the bulb.
15
By repeating the process the speck may be finally driven into the top
of the tube, where it will do no harm. In cooling off the thermometer
for the last time care should be taken that the speck in the column
be at a point before inversion which is above the temperature of the
cooling liquid, otherwise the column left after cooling down will be
so short that it cannot be driven down on inversion. If it be found
impossible to get the short column down on inversion after cooling,
it may be easily lengthened by jarring the bulb in the open hand,
holding the bulb down. In case there is much air separating the
two columns it will be found impossible to unite them when the
upper column is quite short, the air-speck being so large that the
thread of mercury cannot pass it. In such case it may be necessary
to heat the upper part of the tube quite hot where there is no mer-
cury. This expands the air and brings a slight pressure to bear upon
the top of the mercury. If the thermometer while still hot be jarred
upon the open hand the columns will frequently unite. If all other
efforts fail take the tube from the brass scale and gradually heat the
part above the main column in an alcoliol flame, by running it back
and forth in the flame and twirling it continually in the fingers, in
order to heat it uniformly.
The mercury will be volatilized and scattered along the bore.
Then by heating up the thermometer the main column will take up
the various detached portions. Some thermometers are provided
with an expansion chamber at the top of the tube, and in such case
it is only necessary to heat the bulb until the air-speck has been
driven into the chamber. After that, by holding the bulb down, on
cooling it will be found that the air has remained behind and there
is a continuous column of mercury. In the latter kind of thermom-
eter it will frequently be found that a portion of the mercury has
lodged in the chamber, and is entirely separated from the column
in the tube. In such case a slight jar will sometimes send the
mercury down. If this does not avail then the bulb should be
warmed till the column in the tube reaches the mercury in the
chamber. When this is done, after cooling it will be found that the
column is perfect. Sometimes the chamber becomes completely
filled, and no effort can dislodge the mercury. In such case it is
necessary to heat the chamber in an alcohol flame, being careful to
turn the tube in the hand in order to apply the heat uniformly. In
a short time the murcury will be expanded sufficiently to flow down
the tube on its being held with the bulb down. A flame should
never be brought into contact with a thermometer bulb.
MINIMUM THERMOMETERS.
For temperatures below the freezing point of mercury alcohol
thermometers are used, standardized by comparison with a gas ther.
mometer at low temperatures. The alcohol minimum thermometer
16
is the only trustworthy form of minimum thermometer for observ-
ing the lowest temperature reached by the air.
Alcohol thermometers are not as accurate as mercurial. The
alcohol wetting the glass surface makes the reading unequal at
different times. Even with the greatest care an accuracy of 0.6 of a
degree is the best that can be attained. The errors are liable to be
much larger at times on account of air bubbles forming in the column
or part of the alcohol evaporating and lodging in the upper part of
stem.
An index half an inch long made of enamel is fitted loosely in the
bore of the stem and immersed in the liquid. When the temperature
falls the index is carried along the bore and the top stops at the
lowest point reached by the top of the alcohol column. The reading
of the top of the index gives the lowest temperature. It is reset for
another observation by raising the bulb end of the thermometer,
which causes the index to slide down the bore until it stops at the
end of the column of alcohol.
The minimum thermometer is set nearly horizontal, with the bulb
end lower than the top. Jarring by the wind is apt to displace the
index and make it read too low.
Bubbles are apt to develop in the bore or bulb, and, making a break
in the continuity of the alcohol column, make the top read too high.
An instrument must be carefully examined from time to time for
the formation of alcohol in the bore above the column, which causes
the instrument to read too low.
Instructions. The many different ways in which the alcohol becomes
separated make it impossible to unite it by any single method,
different methods being required not only for different conditions,
but also for different thermometers.
Frequently there are only a few short detached portions near the
top, and the index slides freely along the lower portion of the tube
and drops into the bulb. Again, the detached columns are sometimes
found all along the tube, and the index is caught and held at some
point above the main column. In such a case it is advisable to first
bring the index into the bulb, as follows:
First process. Hold the thermometer lightly between the thumb
and fingers and strike the lower end of the metallic scale against the
top of a table, or other firm object; first, however, interposing one
or two thicknesses of cloth, or several folds of paper, so as not to
produce too severe a shock upon the thermometer. The taps of the
thermometer should be made light at first, and the index examined
to see if it has not moved along the tube even a little distance, as
can be told by noticing the exact position of the index in reference
to the graduations on the tube. If several taps fail to move the
index, increase the force of the taps, a little at a time, until the index
starts, after which repeat the operation until the index gets within
17
the continuous column. Here it will fall of its own weight into the
bulb. Generally, this will be all that is necessary to place the index
in the bulb. Sometimes the detached columns will also have been
partly or wholly united. If the column is still broken in places the
observer should try a few more taps and quickly examine, very care-
fully, if very small portions of the alcohol cannot be seen slowly
moving along the sides of the tube toward the main column. If this
is the case a continuation of the taps will unite the columns; on the
other hand, and in case the index cannot be made to move with quite
hard taps, it is advisable to try some of the methods described next,
being careful always to avoid carrying any process so far as to
endanger breaking the thermometer.
Second process. Grasp the thermometer securely a little below the
middle, with the bulb end down, and strike the edge of the metal
back opposite the broken column sharply against the fleshy portion
of the palm of the other hand, or, if necessary, against a small block
of wood held in the hand. A continued jarring in this way often
causes the alcohol to run down, though in many cases a large number
of taps are necessary. Observers should, therefore, not give up if
the column does not unite at once, but should watch very closely for
the movements of small portions of alcohol along the sides of the
tube. Here, again, care must be exercised not to strike too hard,
and to hold the thermometer by the metal back in such a manner as
not to squeeze or press against the stem of the thermometer itself.
When the bore of the thermometer is large the above process is
almost sure to unite the column. Good results are also obtained
with thermometers of fine bore, though the latter often require some
time if the column is badly scattered.
Third process. This method can also be used in place of those
above, and is sometimes effective in forcing the index into the bulb.
Grasp the thermometer a little above the middle, holding it horizon-
tally, clasping the fingers and hand firmly against the edges of the
metallic back, but not so as to bring any pressure upon the glass tube,
which should be turned toward the person and with the bulb toward
the front. With the thermometer in this position and about as high
as the head, and the arm free from the body, quickly lower the arm
and hand a foot or more, turning the wrist at the same time, so that
the bulb of the thermometer describes a somewhat circular path
downward through the air, stopping the motion with a sudden jerk
just as the thermometer is vertical. If the thermometer is grasped
properly a very violent motion can be given in this way without
danger. It will sometimes be necessary to repeat the operation a
large number of times to entirely unite the detached columns.
When all the bubbles have been removed from the alcohol column,
the observer can then see how the instrument works. Hold the ther-
mometer vertically and warm up the bulb by holding it in the hand;
18
then turn the instrument upside down. Watch the index as it glides
along the tube ; when it strikes the top of the column it will at once
stop. This operation of bringing the index to the top of the column
is called " setting" the thermometer. Next hold the thermometer
horizontally and remove the hand from the bulb. As the latter cools
off the index will be dragged backwards toward the bulb, but always
remains at the end of the column of alcohol. It is a good plan to
hasten the cooling by placing a little wet cloth or piece of ice against
the bulb. When you have watched the index go down with the
column, warm the bulb again with the hand. The column will go
up immediately, but the alcohol will flow around the index and leave
it at the lowest point. That is, the index remains so that its top end
is at the lowest point reached by the alcohol column, and the mini-
mum temperature is indicated in this way. The thermometer must
be held horizontally throughout these operations.
When the thermometer is not in use for observation it is a good
plan to hang it up, as bubbles are less likely to form in the tube in
this position.
MAXIMUM THERMOMETERS.
For observing the highest temperatures occurring during the day
a maximum thermometer is used. The form of maximum in use by
the Weather Bureau is a mercurial thermometer with a contraction
in the bore of the tube near the bulb.
When cooling of the instrument sets in the thread of mercury in
the bore separates from the rest at the point of contraction, leaving
the top of the column near the highest temperature reached. It is reset
for another observation by whirling it on a pivot at the top of the
metal strip to which the tube is attached. The centrifugal force
developed drives the detached thread back to the main body of
mercury.
When a maximum thermometer is not read for several hours after
the highest temperature has occurred and the air in the meantime
has cooled down 15 or 20, the highest temperature indicated by
the top of the detached thread of mercury may be too low by half a
degree from the contraction of the thread.
When the fall of temperature from the highest point is very slow
a little of the mercury may pass down before the thread breaks,
especially when there is no wind to cause a slight jarring of the
instrument.
In some instruments the narrowing of the bore develops a strong
capillary action, and when the connection of the column is broken
the detached thread jumps up a little, causing it to register a little
too high. This is most apt to occur in very cold weather when the
detached columns are very short. It also occurs with longer
detached columns when the thermometer is nearly horizontal.
19
The cut below shows the appearance of the maximum and mini-
mum thermometers when properly attached to the wooden board
and supports furnished with the thermometers.
The upper thermometer is the mini-
mum. The lower thermometer is the
maximum. All new maximum and min-
imum thermometers have their respective
names stamped upon the metallic backs.
The maximum thermometer is always
rilled with mercury, sometimes called
quicksilver. All maximum thermome-
ters have a round brass hub-shaped pro-
jection fastened to the top of the back.
The most distinctive peculiarity of the
maximum thermometer, however, is not
so easily seen as those mentioned above.
If observers will hold the thermometer
vertically, with the bulb down, they will
r-; notice that the merciirial column does not
g extend entirely into the bulb. A very
close examination of the thermometer at
the point just above the bulb, where the
mercurial column stops, will show that
the glass tube seems to have been squeezed
almost together at that point, as appears
in the above drawing. . This is just what
has been done, and the passage-way for
the mercury is so fine at that point that
the mercury will only go through with
some difficulty. The observer should next
hold his fingers around the bulb. Pres-
ently the mercury in the bulb, as it be-
comes warm, will be forced to pass the
constricted portion of the tube, flowing
through in little spurts. When the fingers
are removed from the bulb the mercury
below the constriction withdraws toward
the bulb, but none of the mercury above the constriction can get
back and the column remains just the same length as it was when
the bulb was warmest. In this way the maximum temperature
is registered.
Observers sometimes think the above-described constriction in
the tube is a defect, but such is not the case, and no effort should
be made to cause the column to completely unite at this portion of
the tube.
1)3773
20
Some forms of "exposed" thermometers look like maximum ther-
mometers, but observers should never have the least difficulty in
telling one from the other. The maximum thermometers used by
the Weather Bureau always have the constriction, and only maxi-
mum thermometers have the "hub" at the top of the metallic back.
If it is desired to set the maximum thermometer before placing
in position on the supports, this may be done by following the in-
structions given in the "third process" for minimum thermometers,
by which means the column of murcury will be driven back into
the bulb and the instrument "set" at the current temperature.
INSTRUCTIONS FOR SETTING UP MAXIMUM THERMOMETER.
For the support of the maximum thermometer, the long brass pin
with a nut must be screwed into the board in the hole to the extreme
right. The nut must be taken off and the pin slipped through the
hole in the upper end of the instrument, and then secured by replac-
ing the nut and screwing it tight. The plain brass pin must then
be inserted in the hole on the left of the board, and the thermom-
eter placed upon it, so as to slightly incline in that direction. The
end of the pin to which the maximum thermometer is attached must
be occasionally oiled to prevent friction. The maximum thermom-
eter is read by observing the number of degrees upon the scale at the
top of the column of mercury. After having taken a reading, the ob-
server must remove the pin at the left and then take hold of the
thermometer about 3 inches from the top and spin it ar^tmd
several times in the direction of the motion of the hands of a watch,
until the bulb and stem below the constriction are filled with mer-
cury. Care must be taken not to touch the bulb, and also that the
nut is screwed up sufficiently tight to prevent the instrument from
striking against the side of the board to which it is fastened. After
adjustment, gradually raise the instrument to a nearly horizontal
position and insert the pin as before. Care must be taken in ele-
vating the instrument not to raise the bulb too high, as the column
of mercury would then break and run to the upper end of the tube.
INSTRUCTIONS FOR SETTING UP MINIMUM THERMOMETER.
The brass support (a long, thin, narrow piece of curved brass,
containing two screw-holes near the center), to which the minimum
thermometer is attached, will be secured to the board in the follow-
ing manner :
The first screw-hole will be made 8 inches from the inner edge of
the bevel at the end of the board on the right, and $/& inch below
the inner edge of the bevel on the top of the board.
After securing the brass support to the board with the// screw,
attach the thermometer by screwing it to the support, and let the
lower end of the thermometer-scale rest in the notch cut in brass
21
support to the left. Then bring the left end of the support to such
a position that the upper edge of the thermometer-scale will run
exactly parallel with the edge of the board. The second screw will
then be inserted, which will secure the brass support firmly to the
board.
The minimum thermometer, when attached to the support in this
manner, will then be exactly horizontal, which position is best
adapted to prevent any movement of the index not caused by the
actual changes in temperature. The top of the thermometer must
be fastened by the small brass screw upon the support and the
lower end dropped into the notch to the left, after having been
raised sufficiently to allow the small index in the tube to move
down to the top of the column of spirit. This instrument is read by
observing the number of degrees on the scale where the top of the index
rests.
If, at any time, the column should be found to be broken and
bubbles are observed in the tube, the instrument should be taken
off the supports and an effort made to unite the column, as given
above.
To " set " the minimum thermometer after a reading has been
made, the bulb, or lower end of the thermometer, must be elevated
a few inches until the index moves down to the end of the column
of alcohol, and then carefully lowered into the notch at the left of
the brass support, as before.
After resetting the maximum and minimum thermometers, the
top of the mercurial column of the maximum and the top of the
alcohol column of the minimum should read alike.
Example : The above illustration represents the thermometers
just after they have been set. It will be seen that the top of the
mercurial column of the maximum indicates a reading of 89. The
top of the alcohol column and the top of the index of the minimum
show the same reading, 89. This indicates that the two instru-
ments have been properly set.
The instruments must be set, in the manner described, once
each day, immediately after taking the observation. In no case
must they be set at any other time.
The wooden boxes and packing material received with these ther-
mometers should be carefully preserved for use in returning instru-
ments.
In packing thermometers for transportation each instrument must
be carefully wrapped in sheet cotton; the whole surrounded with
excelsior, or other packing material, in the wooden box, and, to pre-
vent shifting, all spaces should be filled with cotton. The lids of the
wooden boxes should always be secured with screws, as the jarring
resulting from driving nails into the wood is liable to break the
thermometer.
22
THERMOMETER SHELTER.
To take the temperature of the air the thermometers are set up
inside of a cubical wooden lattice work inclosure called a shelter.
To get the temperature of the air accurately a thermometer must be
protected from the direct rays of the sun, which cause it to read too
high. Without a covering in the night time by radiation to the sky
a thermometer is apt to read too low. The ground is cooler than the
air at night, but the effect of ground radiation on a thermometer is
inappreciable at a greater height than 4 feet above the ground.
A thermometer in quiet air in the sunshine may read 10 or
more higher than the air temperature, depending on the strength
of the wind prevailing at the time. With the air perfectly calm
it may read even 20 higher. With a wind of twenty miles
an hour it will read only a few tenths of a degree higher than the
temperature in the shade, which is the true temperature of the air.
Moving particles of air coming continually in contact with the bulb
rapidly carry away the heat received from the sun. When there is
no wind a thermometer bulb creates a local atmosphere of warm air
around it. In a vacuum where all contact with air is shut off, a
thermometer in the sunshine becomes greatly heated. A thermom-
eter in the sunshine whirled rapidly will read about half a degree
higher than the true air temperature.
The reading of a thermometer in the sunshine in nearly quiet air
is not a meteorological datum of any value.
The form of shelter shown below and described, has been found
after years of experience to be the best adapted for the purpose.
fi"
8*
r^^
6"
8"
36
DJ
36"
B_
42
36'
42"
Section thr<f
Scale 1=50" Scale 1 = 5
4"
Section, thro* A.B
Scale 2*5"
FlG. 2. DESIGN FOR THERMOMETER SHELTER.
The frame is cubical, 3 feet on a side. The bottom is of close
boards, pine, % inch thick. The roof is double, sloping 8 inches
-23
from front to rear, with 6 inches between. The high or front side
is made to face north. The front has a door 15 inches wide the
whole length of side, and opens down. The sides are of blind work;
the slats of white pine 3^ inches wide and ^ inch thick, slop-
ing at an angle of 45 to the horizontal. The distance from
center to center is i% inches. Each slat has a strip ^ inch wide
and X i nc h thick nailed along its length on the inside flush
with the bottom. The frame is in four parts and furnished with
screws for putting together. The bottom has one piece loose and
hinged, so as to allow of dropping down, and a button to hold it up.
Inside there is a frame for holding the thermometers, consisting of
two upright strips i by 3 inches fastened to long strips screwed to
the right and left rails of the frame with a strip i by 2^2 inches be-
tween the thermometers. It is painted white. This shelter should
be exposed upon a free grass plat where there is no obstruction to
the wind, and at a height of at least TO feet above the sod. An expo-
sure from the roof of a building is not objectionable, provided a plat-
form 20 feet square be first laid and the shelter be raised 8 feet
above the roof. The good ventilation of a roof is especially valua-
ble. An exposure 4 feet above sod, especially among trees, or where
there is very little natural ventilation, is objectionable, from the
fact that under such conditions radiation from the sod into space
abnormally cools the sod, and that in turn cools the air above it.
This effect is especially active at and a few hours after sunset. The
expense of such an exposure as that just described may deter many
observers from adopting it, and in such case the following substitute
is suggested :
WINDOW OR WALL SHELTER.
As its name implies this may be used from the iraside of a house
or it may be placed upon a wall and read from the outside ; in either
case the protection for the thermometers is the same and may be
very easily prepared by any one. Ordinarily a wall which should
invariably be one looking due north or only a few degrees to the
east or west of north will give too low a temperature by day, except
possibly in winter, and always too high a temperature by night.
The reason for this is not far to seek. During the daytime a large
wall does not gain the temperature of the free air but is nearly
always below it, while the reverse is true at night.
These conditions are specially prominent in the case of a large
brick or stone wall. The two effects above may be partly counter-
balanced by the following considerations : First, the effect of the
coolness of the wall by day may be offset by heat reflected and radi-
ated from other walls or surroundings; second, the warmth at night
may be offset in like manner by radiation to the sky. This will
readily suggest a form of exposure adopted by many, one very easy
24
to manage, and being the least expensive of any. Select a north
window, preferably of an unoccupied room, especially in winter.
Fasten the blinds open at right angles to the wall of the house in
order to shield from the effects of the 'direct solar radiation on the
north side both morning and evening. Fasten a narrow strip, per-
haps 3 inches wide, across the window outside and from 8 to 12
inches from the window pane ; to this fasten the thermometers.
Some difficulty will be experienced in setting the maximum ther-
mometer and in wetting the wet bulb if the room is occupied, as the
heated air in winter will disarrange the readings of the self-regis-
tering thermometers. This may be partially obviated by opening
the upper window and conducting all operations through it. In this
case the heated air rises and does not affect the readings. If there is
no wind, or if the wind is south, the greatest disadvantage arising
from this exposure will be the lack of ventilation of the wet bulb.
This may be partly obviated by working a fan hinged near the wet
bulb and operated by a handle in the room.
(1) The most important consideration is as full and free natural
ventilation as is possible. This is essential even if an artificial ven-
tilation be employed for the dry and wet bulbs. Since the maximum
and minimum temperatures are necessarily unventilated, the shelter
itself should give accurate results for these.
(2) Provision should be made to avoid effects of direct solar radi-
ation, and also of heat reflected and radiated from surrounding
objects.
(3) Rain should be excluded, but only, as far as possible, in con-
nection with (i). During a rain-storm the dry and wet bulbs must
necessarily give the same values, the air being nearly saturated;
hence a wetting at this time is not harmful.
(4) All perraanent heating effects from warm walls, chimneys, etc.,
should be carefully avoided.
DAILY MEAN TEMPERATURE.
The mean or average daily temperature at a place is the mean of
the twenty-four observations made at a place at every hour of the
day. Hourly observations of temperature are made at only a few
places over the world. Approximate values of the mean daily tem-
perature are obtained by various short processes.
The mean of the highest and lowest temperature of the day, as
observed with a maximum and minimum thermometer, gives a tem-
perature on the average about i.o higher throughout the year
than the hourly mean at places in the United States. This is the
mean adopted by the Weather Bureau for the observations at the
regular meteorological stations. In England the same mean gives
the temperature 0.6 of a degree too high throughout the year, being
1.2 too high in August and 0.3 too high in January.
25
One-half the sums of the temperatures at 9 o'clock, morning and
evening local times, gives the mean too small by about 0.5 of a degree.
One-half the 8 o'clock, morning and evening, gives the tempera-
ture in the United States only a few tenths of a degree below the
mean of the day.
When it is possible to observe the temperature at 7 a. m., 2 p. m.,
and 9 p. m., a very close approximation to the mean hourly tempera
ture of the day can be obtained by taking one fourth of the sum of
the temperatures at 7 a. m., 2 p. m., and twice the 9 p. m.
Example: 7 a. m. + 2 p. m^+ 2 (9 p. m.)
This combination is recommended where the observers can con-
veniently make the observations at those hours.
SOLAR RADIATION THERMOMETER.
A solar radiation thermometer consists of a mercurial thermometer
inclosed in a glass tube from which the air has been exhausted.
They are commonly used in pairs,-one with a black bulb, the other
bright, and are exposed side by side in the sun. They are known
as the bright and black bulb in vacuo. The black bulb will read in
the sunshine from 30 to 60 higher than the temperature of the air
in the shade. The temperature attained depends on the rate at
which heat is being received from the sun by the bulb and radiated
to the glass inclosure surrounding it, which is nearly the tempera-
ture of the air.
The thermometer shown in Fig. 3, is usually made as a maximum
with constriction in bore of stem. The inclosing bulb is about 1.5
inches in diameter. The highest temperature occuring during the
day is registered by the instrument, and it is reset each day for
another observation.
FIG. 3. FIG. 4.
The difference of bright and black bulb shows the difference in
the heating effect of the sun on the air at different times. When
26
there is a great deal of moisture or dust suspended in the air more
of the sun's heat is absorbed in passing through it than when there
is very little. The more the air is heated the less the bulb. It is
not a good measure, however, as the difference in the bulbs depends
on so many things besides the clearness of the air.
The thickness of the film of blacking on the bulb affects the dif-
ference; also the size of the bulb the thickness of the glass bulb of
the inclosure, and variations in the nature of the glass not percep-
tible to the eye; also the depth of air through which the sun's rays
come. Some varieties of glass transmit more of the sun's heat than
others. A great deal too depends on the perfection of the vacuum.
The presence of the least trace of air depresses the reading. Instru-
ments the same to all appearances, when exposed side by side, will
differ as much as 6 in the temperatures indicated.
Nothing of any importance has yet been derived from observations
of these instruments. No way has yet been devised of making
different pairs comparable.
At high altitudes, as on mountain tops, the black bulb in sunshine
may read as high as the boiling-point of water.
In the arctic regions, in summer, the difference between the bright
and black is sometimes as great as 96.
The name radiation thermometer is also applied to an alcohol
thermometer exposed in the open air on the ground in the night
time to get the lowest radiation temperature of the soil. The ther-
mometer shown in figure 4 is the same as the ordinary minimum,
except that there is a--protecting glass tube over the graduations to
shield the graduation of the scale from the action of the dew and
prevent its being washed out. During the night in still air it may
take on a temperature 10 lower than that of the air a few feet above
the ground.
When a thermometer is wetted repeatedly or put in alcohol or
ether, the graduation becomes indistinct or illegible from the marks
in the etching washing out. To replace the marking, artist's black
pigment is used. It should be rubbed on the thermometer when the
tube is quite dry, and the tube then wiped with glazed paper to
remove the pigment not in marks.
THERMOSCOPE.
A sealed glass tube containing an alcohol solution of camphor
gum is sometimes used as an indicator of temperature changes.
When the temperature is high the camphor is all dissolved and the
liquid is clear. At a low temperature the camphor crystallizes out,
forming a fleecy whitish looking mass. A thermoscope of this kind
is sometimes sold mounted on the same board with a thermometer,
and is often erroneously supposed to indicate changes in pressure,
or the electrical condition of the air.
27
WATER VAPOR IN AIR.
The air contains vapor of water transparent and colorless like its
other gaseous components. It only becomes visible on condensing
to fog or cloud, which is only water in a fine state of division, the
particles varying in diameter from 0.0006 to 0.0050 of an inch. The
amount is very variable at different times, even in the vicinity of
the ocean, depending mainly on the temperature of the air. On
very cold days it forms no more than the one-thousandth part of the
air. On very warm days it may be as great as one-fiftieth part.
The amount of moisture chat can exist as vapor in the air depends
on the temperature. There is a certain pressure of vapor corre-
sponding to every temperature which cannot be exceeded ; beyond
this there is condensation. This temperature is called the tem-
perature of saturation for the pressure. When the temperature of
the air diminishes until the saturation temperature for the vapor con-
tained is reached, any further fall causes a condensation of moisture.
The temperature at which this occurs at any time is called the
dew-point temperature of the air at that time. The less the quantity
of moisure the air contains the lower will be the temperature of its
dew point.
This property of vapor is made use of to determine the pressure
of vapor contained in the air at any time. The number of degrees
the dew point is below the temperature of the air is called the
depression of the dew point.
The relation of water- vapor pressure and temperature has been
very thoroughly investigated by skillful experimenters on account
of its importance in the theory of the steam engine.
For different saturation temperatures the vapor pressures, in
inches of mercury, and the weight of vapor, in grains, contained in a
cubic foot of air are as follows :
Temperature Vapor pres- Weight in a
of satura- sure in cubic foot,
tion. inches. grains.
0. 038 0. 56
10 0. 063 0. 87
20 0. 103 1. 32
30 0. 164 1. 96
40 0. 246 2. 85
50 0. 360 4. 08
60 0. 517 5. 74
70 0.732 7.98
80 1.022 10.93
90 1. 408 14. 79
100 1. 916 19. 77
The quantity of water contained in the air is nearly proportional
to the vapor pressure. The air is never perfectly saturated, not
even when rain is falling ; neither is it ever perfectly dry at any
place.
The number expressing the vapor pressure in the air at any time
divided by the number expressing the pressure of saturation for the
28
temperature prevailing at the time is the fraction of saturation, and
is called the relative humidity. It is expressed in hundredths of
the pressure at saturation and is called percentage of relative
humidity. With the air at a temperature of 60, for instance, if the
pressure of vapor contained is found to be 0.420 of an inch, the
pressure at that temperature for saturation being 0.5 17, the percent-
age of relative humidity is the one divided by the other, expressed
in hundredths as the unit, or 81 per cent.
Relative humidity expresses relative amount of moisture in the
air only as long as the temperature of the air remains constant.
For this reason relative humidity is an imperfect datum. At a low
temperature even a high relative humidity represents a very small
amount of vapor actually in the air, while a low relative humidity
at a high temperature represents a great deal. At a temperature
of 30, for instance, a relative humidity of 90 per cent, corresponds
to 0.149 f an i nc h vapor pressure, while 50 per cent, at 80 corre-
sponds to a pressure of 0.511, or more than three times as much as is
contained at the temperature of 30.
The amount of moisture in the air is ascertained indirectly by
observing the temperature at which dew is deposited, or by deter-
mining the vapor pressure by means of the difference in indication
of a dry and wet bulb thermometer.
PSYCHROMETER.
Two thermometers, one with wet and the other with dry bulb,
when used to determine the vapor pressure in the air, is called a
psychrometer. The wet bulb consists of an ordinary mercurial
thermometer with a wrapping of muslin on the bulb kept saturated
with water. The water evaporating from the muslin cools the bulb.
The dryer the air the greater the amount of evaporation and the
more the bulb is cooled, and consequently the reading of wet bulb
is lower the dryer the air.
From a series of comparisons of the indications of a dew-point
apparatus and a psychrometer the relation between the pressure of
the vapor in the air and its dependence on the difference between
the reading of the dry and wet bulb thermometer has been ascer-
tained. Tables showing this relation are given here. With the differ-
ence of dry and wet bulb and the temperature of the air, the reading
of the dry bulb, the temperature of dew point of the air is obtained
from one table and the relative humidity from the other.
The result found for vapor pressure with a psychrometer varies a
little in still air, depending on whether the wet bulb is spherical or
cylindrical. It also depends on the absolute size of the bulb and
whether the stem above the bulb for an inch or so is wrapped with
the wet muslin. All of these effects are obviated by whirling the
psychrometer so as to cause a brisk renewal of air around the bulb.
29
When whirled before making the readings, instruments of the most
diverse patterns are strictly comparable..
Where the highest accuracy is required the most minute correc-
tions of the thermometers have to be applied. Small errors in the
observed temperatures affect the deduced vapor pressures very much.
The tables given are based on psychrometer readings uncorrected
for the difference of temperature between the bulb of the wet ther-
mometer and its stem, the stem being at the temperature of the air
while the bulb is a variable number of degrees lower, depending on
the dryness of the air. For a long stem this correction may amount
to 0.3 or 0.4 of a degree.
SLING PSYCHROMETER.
For values of dry and wet bulb temperatures the most accurate
method yet devised consists in the use of dry and wet bulb ther-
mometers fastened together and whirled quite rapidly. Any one
may very readily prepare this instrument. The thermometers may
be fastened back to back or side by side, the wet bulb an inch or so
lower than the dry; then a rather strong wire or a good many folds
of a thinner one should be passed through the hole at the top of the
scale, and to this a stout cord about 12 inches long should be fastened.
A glove finger will serve to protect the finger while whirling. The
method of use is very simple. First wet the muslin by immersion
and wait about a minute till the wet bulb has fallen somewhat (this
is specially necessary in a very dry air, as otherwise the muslin may
become dry before it has reached its lowest reading), then whirl the
thermometers about 50 times, stop and read the wet bulb, then whirl
20 times and again read. If the temperature of the wet bulb has not
changed it may be considered as the correct value. If there has been
a change to a lower reading continue the alternate whirling and
reading until the wet bulb reaches its lowest reading or one slightly
higher than the one previous. The lowest reading is to be recorded.
A velocity of 12 feet per second is ample.
Great care should be taken never to allow the muslin to become
dry or even partly so. At night the whirling may be done at any
convenient spot where there is a good ventilation. The temperature
should be taken at least 6 feet above sod or at any height greater
than that. If there is a wind blowing the observer should stand to
leeward; if there is no wind, in cool weather, it may be necessary to
walk about while whirling in order to overcome any possible vitiation
of the reading from the heat of the body. When the sun is shining, in
the daytime, the temperature should be taken in the shade of a
small object, high tree, or even umbrella, but not in the shade of a
wall or large house. The use of this instrument when the wet bulb
is covered with ice is specially satisfactory. The lowest reading at
any time may be obtained in three minutes, while with a rather
30
close window shelter, when the air is still, it will require a delay of
an hour tor even an approximate value.
HAIR HYGROMETER.
A human hair when freed of oil, by soaking in ether for twenty-
four hours, has the property of changing by about one-thirtieth part
of its length between a very dry and very moist condition of the hair
at ordinary temperatures.
A hair hygrometer consists of a hair about 12 inches in length
mounted in a brass frame, the lower end wound once around a pulley
and stretched by a weight of about i gramme, or 15.4 grains Troy.
As the pulley turns with the varying length of hair dependent on
the dryness of the air, an attached index moves over a graduated arc,
indicating the percentage of humidity or relative humidity. It is
graduated with reference to a dew-point apparatus or a psychrometer.
It is not an accurate instrument, its results being complicated with
changes of temperature. It is only used in closed spaces where
other means of observing vapor pressure are not available. It gives
a rough result very quickly. It is sometimes used for humidity ob-
servations at temperatures below zero.
BAROMETER.
The air presses on everything at the surface of the earth with a
pressure equal to the weight of the column of air above it to the
limit of the atmosphere. This pressure is on the average about 14.67
pounds to the square inch, and corresponds to the pressure of a
column of mercury about 30 inches in height. The pressure of the
air is continually varying within small limits. Variations in pres-
sure are not noticeable to the senses except in the case of sudden
great changes.
The barometer is an instrument used to measure the pressure of
the air. Pressures are expressed in the equivalent height of a
column of mercury reduced to the temperature of freezing point.
The barometer is a glass tube open at one end and closed at the
other, about 38 inches long and % inch in interior diameter. The
open end dips into the cistern of the instrument containing mer-
cury which extends inside the tube up to a height corresponding
to the pressure of the air. The tube above the column of
mercury contains no air. The vertical height of the level
of the top of mercury column above the level of mercury in
the cistern, in inches and parts of an inch, is called the barometer
reading. This height is constantly varying within small limits with
the changing pressure of the air.
The barometer is first set up by the maker by filling the tube
with mercury and inverting it with the open end immersed in the
mercury in the cistern, the end being closed temporarily with the
gloved finger until it is immersed in the mercury. When the finger
31
a
is removed the mercury runs down the tube, oscillating back and
ferth and finally coming to rest at a height corresponding to the
pressure of the air outside.
The observation of pressure consists in ascertaining the height of
column at any time by means of the scale attatched to the instru-
ment. For this purpose an ivory point, the lower extremity of
which is the zero of the scale, is fixed to the frame-work of the
instrument, on the upper portion of which is the graduated scale
and vernier. The mercury in the cistern is brought in contact with
the ivory point and the vernier of the scale is adjusted to the top of
the column ; the reading of the scale will then give the height of
the column of mercury.
Placing. The barometer should be placed in a room of a tempera-
ture as uniform as possible, and not exposed to the sun. It must
be suspended so that the top of the column will be at the height of
the eye, near a window, in such a manner as to be lighted perfectly
without exposure either to the direct rays of the sun or to the cur-
rents of the air which are always to be found at the joinings of the
windows. When the barometer has to be fixed to the wall, as is the
case with all the self-recording and some other
barometers, care must be taken to secure the tube
( in a position perfectly vertical, regulating it by the
plumb-line, first in the front, then at the sides, in
two vertical planes cutting each other at right angles.
When the instrument is so constructed as to take
its equilibrium itself, as the Fortin barometers and
those of J. Green, it is enough to hang it on a strong
hook. These conditions being fulfilled, the rest of
the arrangement may be varied according to the
nature of the localities. For the Fortin and Green
barometers the following arrangement is convenient,
and may be almost everywhere adopted. (See Fig. 5.)
A small elongated box (a b), some inches longer than
the barometer and a little broader than its cistern, is
firmly set against the wall (w w'), near the window,
in such a manner as to open in a direction parallel
to the panes ; at the summit (a) it has a strong hook
(h /$'), which extends beyond the box about 2 or 3
inches, and on which the barometer is suspended.
The instrument remains generally in the box, which
is closed by a movable cover, and which protects it
from external injuries, from dust, and from the direct
radiation of warm bodies, or the currents of air from
F 5 the window, and diminishes the effect of the too
sudderfvari-ations of temperature. When it is to be observed, the
barometer is taken by the upper end of the tube, and the suspending
32
ring- is made to slide toward the end of the hook. The instrument
is then in the full light of the window, in front of which the observer
places himself ; the summit of the mercurial column, as well as the
surface of the mercury in the cistern, are completely lighted, and
the reading becomes easy and certain. Moreover, the slight oscillat-
ing movement impressed on the instrument by changing its place
breaks the adherence of the mercury to the glass, and thus prepares
a good observation. After the reading, the barometer is again
slipped gently into the box, and this is closed.
It has been found that even with the exercise of care the barom-
eter cistern strikes against the box when it is pushed in, and in con-
sequence the instrument deteroriates quite rapidly. To avoid all
possibility of injury from this cause it is only necessary to make two
oblong sets of openings in the back of the box, one just at the ivory
point about 3 inches long, and the other at the vernier some 8 inches
long, and place in these plates of glass. If now the barometer box
be suspended vertically in a north window it will be a very simple
matter to make readings by opening the box and adjusting the
mercury to the ivory point and the vernier to the top of the
column, without moving the barometer.
Observation. Note the degree and the tenths of degrees of the
thermometer attached to the instrument; for it will be seen that the
heat of the observer's body soon makes it rise.
Incline the instrument gently, so as to render the mercurial column
very movable; then, after having restored it to rest, strike several
slight blows upon the casing, in such a manner as to impress on the
mercury gentle vibrations. The adherence of the mercury to the
glass will thus be destroyed, and the column will take its true
height corresponding to the outside pressure of the air.
Bring, by means of the adjusting screw at the bottom, the surface
of the mercury to the zero of the scale.
In the barometers with an ivory point, as the Fortin, Newman,
and Green barometers, the extremity of this point is the zero of the
scale, which must be brought into exact contact with the surface of
the mercury. This takes place when the point coincides exactly
with its image reflected below by the mercury. This method is very
good when the surface of the mercury is perfectly pure and brilliant.
It is generally dimmed by a slight layer of oxide, which makes the
coincidence of the point with its image uncertain. It is safer to
judge of the contact in a different manner. From the moment when
the point does more than touch the surface, it forms around itself,
by capillary action, a small depression, which, breaking the direction
of the reflected rays, becomes immediately very easy to discover.
It is enough, then, to raise the mercury so as slightly to immerse the
point; then to lower it gradually iintil the little depression dis-
appears. If care is taken to make a good light fall on that portion
33
of the mercury which is under the point, and to use the aid of a
magnifier, the adjustment of the point thus made becomes not only
easy, but very certain, and the errors to which we are liable are
almost insensible, for they do not exceed two or three hundredths
of a millimeter, or a thousandth of an inch.
The level being thus adjusted to the zero of the scale, proceed to
observe the height of the summit of the column. Take hold of the
instrument with the left hand, above the attached thermometer,
without moving it from the vertical; tap it gently in the neighbor-
hood of the top of the column; then, by means of the screw, lower
the slide which carries the vernier, until the plane passing through
the two lower opposite edges of it is exactly tangent to the summit
of the meniscus that is, the convexity which terminates the column.
This is the case when, placing the eye exactly at the height of the
summit of the column, it is seen without there being any trace of
light between the summit and the edge of the ring. To be certain
that the barometer has remained quite vertical during its operation,
leave it to itself, and, when it is at rest, look again to see whether the
ring has remained tangential to the summit of the column. If it
has not, the verticality has been disturbed; it must be adjusted
anew. It is necessary, at the same time, to examine if the adjust-
ment of the surface of the mercury in the cistern has remained the
same.
Nothing more, then, remains than to read the instrument. In the
English barometers the inches and tenths of inches are read directly
on the scale, the hundredths and thousandths on the vernier. In
the French barometers, with the metrical scale, the centimeters and
millimeters are read on the scale, and the fractions of millimeters
on the vernier.
THE VERNIER.
The vernier is a contrivance for measuring fractional portions of
one of the equal spaces into which a scale or, as commonly known,
a limb is divided. We will call the fixed portion of the barometer,
which is divided into equal parts, the scale, and the part which
moves upon it by means of the screw and ratchet, the vernier. A
simple inspection will indicate the nature of the spaces or equal
parts of the scale. In the common barometer there are inches and
tenths, or centimeters and millimeters. Ordinarily the spaces on
the whole length of the vernier are one more than on the part of the
scale which it covers : /. <?., if the vernier has ten spaces the scale
has nine in the same length. Determine the value of the smallest
space on the scale (in the common Green barometer this is one-
tenth inch), divide this by the number of spaces on the vernier, and
we get immediately the least count of the vernier. We have then the
following rule : The least count of a vernier is equal to one of the
34
spaces of the scale divided by the number of equal parts on the
vernier.
The reading of the instrument depends on the distance from the
zero point or the beginning of the scale to the zero point of the
vernier. If we take a vernier and make its zero point coincide with
one of the divisions on the scale we shall find the second line exactly
the least count of the vernier below the second line of the scale; or,
in other words, if we move the vernier until its second line coincides
with the one just above the first line on the scale, just referred to,
we shall move the zero just the least count above its first position.
In the same way the zero of the vernier may be made to coincide
with other divisions on the limb, and the distance moved will depend
on the number of the line on the vernier above its zero which is
coincident with the line on the scale. We have then the simple rule
for reading a vernier. Read the scale up from its zero, or in the
direction in which the figures on the graduations increase up to that
line of the scale just below the zero of the vernier. Call this the
reading of the scale. Find the number of the line on the vernier,
counting the first line above the zero as i, which coincides most
nearly with aline on the scale; multiply the least count of the vernier
by this number; this will give the reading on the vernier; the sum
of these two readings is the reading of the instrument.
The observer is advised to test his ability to read the vernier by
setting it at various points and then reading. After a time one
reads the vernier naturally, without being obliged to follow any
fixed rules. It will seldom occur that a line on the vernier exactly
coincides with one on the scale, and after a little practice one will
be able readily to split the least count; for example, if any two con-
tiguous lines of the vernier lie between and exactly equidistant from
two on the scale, the least count will be exactly halved. It is a very
good plan, in order to avoid serious mistakes, at first to estimate the
position of the zero line of the vernier on the scale; this will give
the approximate value of the reading and will check the reading
made from the vernier.
To read the vernier, we must look out for the line that coincides
with one of the divisions of the scale. The number of this division
of the vernier, proceeding from zero, indicates the number of tenths
of millimeters, or of hundredths of an inch, which must be added to
the whole number given by the scale. If none of the divisions of
the scale coincides exactly, we estimate by the eye, in decimals, the
quantity by which the vernier must be lowered to obtain a coinci-
dence, and this is added to the fraction already obtained. This will
be hundreths of millimeters in the metrical barometer, and thou-
sandths of inches in the English barometers.
The following figures will serve as examples; the instrument is
an English barometer:
35
In Fig. 6 the regulating line, which is the lower edge of the vernier
ring, coincides exactly with the line of 30 inches on the scale. The
zero and the tenth division of the vernier are also in exact coinci-
dence; that is to say, there is no fraction. We shall read then 30.000
inches.
In Fig. 7 the regulating line does not fall upon any of the divisions
of the scale, but between 2 9l % and 29-^- inches. There is then a
fraction which must be read on the vernier. Seeking which of these
divisions coincides with that of the scale, we find that it is the fifth;
we shall write then 29.250 inches.
-10
-10
80-
FIG. 6.
FIG. 7.
FIG. 8.
In Fig. 8 we see that the height falls between 30 inches and
inches; no line of the vernier coincides exactly; but the line 7 is a
little above, the line 8 is a little below, one of the lines of the scale;
the fraction falls, then, between seven and eight hundredths. Esti-
mating in tenths the distance the vernier passes over between the
coincidence of 7 and that of 8, the tenths of a hundredth, or the
thousandths are obtained. In the latter case the distance above 7 is
greater than the half; it will read then, greater than 30.075 and
less than 30.080, or about 30.077. It will always be easy to judge
whether the top approaches nearer the upper coincidence than
the lower coincidence; in the former case the fraction is greater
than .005; in the latter it is smaller than .005. The error which will
be committed in this estimate will remain less than .005; after
a little practice it will rarely exceed .002, always supposing the scale
is well graduated. For this reading, as well as for the others, it
is particularly important to have the eye exactly at the height of
the line to be determined.
9377 3
36
During the whole time of the observation of the barometer the
observer must endeavor to protect it as much as possible from the
heat which radiates from his body. But the best way is to learn to
observe rapidly. All the operations take longer to describe than to
execute; one or two minutes, if the instrument be in place, three
minutes, if it is to be taken from its case and put back again, are
sufficient for a practiced observer to make a good observation.
The barometer consists of a brass tube (Fig. 9) terminating at
top in a ring A, for suspension, and at bottom in a flange B, to which
the several parts forming the cistern are attached.
The upper part of this tube is cut through so as to expose the glass
tube and mercurial column within, as seen in figure. Attached at
one side of this opening is a scale, graduated in inches and parts;
and inside this slides a short tube C, connected to a rackwork
arrangement, moved by a milled head D; this sliding tube carries
a vernier in contact with the scale, which reads off to ^ (.002) of
an inch.
In the middle of the brass tube is fixed the thermometer E, the
bulb of which being externally covered, but inwardly open, and
nearly in contact with the glass tube, indicates the temperature of
the mercury in the barometer tube, not that of the external air. This
central position of the thermometer is selected that the mean tem-
perature of the whole column may be obtained, a matter of im-
portance, as the temperature of the barometric column must be taken
into account in every scientific application of its observed height-
The cistern (Fig. 10) is made up of a glass cylinder F, which allows
the surface of the mercury q to be seen, and a top plate G, through
the neck of which the barometer tube / passes, and to which it is
fastened by a piece of kid leather, making a strong but flexible
joint. To this plate, also, is attached a small ivory point //, the
extremity of which marks the commencement or zero of the scale
above. The lower part, containing the mercury, in which the end
of the barometer-tube / is plunged, is formed of two parts / /, held
together by four screws and two divided rings / ;;/, in the manner
shown in figure. To the lower piece j is fastened the flexible bag
N, made of kid leather, furnished in the middle with a socket /,
which rests on the end of the adjusting screw O. These parts, with
the glass cylinder F, are clamped to the flange B by means of four
long screws P and the ring R; on the ring R screws the cap S, which
covers the lower parts of the cistern, and supports at the end the
adjusting screw O. G, i,j, and k are of boxwood; the other parts are
of brass or German silver. The screw O serves to adjust the mercury
to the ivory point, and also, by raising the bag, so as to completely
fill the cistern and tube with mercury, to put the instrument in con-
dition for transportation.
Some cisterns are made of an iron or glass cylinder with a
plunger working in it air-tight.
37
FIG. 9.
FIG. 10.
38
CORRECTION OF BAROMETRIC OBSERVATIONS.
Corrections must be applied to all barometer readings in order
to bring the indications of different instruments into harmony with
each other before they can be used for comparative purposes. Some of
these corrections have reference to the special instrument, while
others are applied to the reading of any instrument taken under the
same conditions. The corrections of the former class are two in
number:
I. Instrumental error.
II. Capillarity.
Those of the latter class are also two:
III. Temperature.
IV. Altitude above sea level.
I. Correction for instrumental error. This is applied according to
the error discovered in the individual instrument when compared
with the standard. It is either additive ( + ) if the barometer reads
too low, or subtractive ( ) if it reads too high, in order to bring it
into agreement with standard.
II. Correction for capillarity. The indications of barometers are
affected by the capillary action between the glass tube and the mer-
cury, the effect of which is constantly to depress the mercury by a
certain quantity nearly inversely proportional to the diameter of
the tube. This correction is included in the correction for instru-
mental error.
The correction is always additive.
This depression is greater in tubes in which the mercury has not
been boiled than in those which have been subjected to this process.
The certificates furnished from the Weather Bureau Office for all
barometers verified there give the results of direct readings of the
columns at different heights, and so include the corrections above
mentioned, in so far as any of them are applicable to the special
barometer under consideration.
Correction for temperature, or reduction (032 F. All bodies are affected
in their dimensions by heat; with few exceptions they expand when
their temperature rises and contract when it falls, and it is there-
fore necessary, in taking any accurate measure of pressure, to know
at what temperature it was taken, in order that we may know what
the length of the column of mercury would be at some definite
temperature, which is taken as the standard. In case of barometers
this standard temperature is taken as 32, and accordingly when
the barometer is at a temperature below 32, considering only the
mercurial column, the correction is additive ( + ), and when it is
above 32 it is subtractive ( ).
If the standard temperature for the brass scale were the same as
that used for mercury, the sign of this correction would change from
39
+ to at 32, but the standard temperature for the scale is regarded
as 62; hence the sign changes at 29 instead of 32, the total cor-
rection being the difference of the two corrections, one for the
temperature of the mercury and the other for the temperature of
the scale. The expansion of the mercury is about ten times as great
as that of the scale.
The temperature of the barometer is given by the attached ther-
mometer, the bulb of which is so placed as to give as accurately as
possible the true temperature of the actual column of mercury.
The corrections are given in the table for each half inch from 24 to
31 inches, as of course the correction depends on the length of the
column of mercury.
In consequence of the great risk of the heat of the observer's person
affecting the thermometer attached to the instrument during the
process of taking a reading of the barometer, the attached thermom-
eter is always to be read first of all, before the reading of the baro-
metrical column is made.
The table at the end of these instructions contains the corrections
to be applied to the readings of barometers mounted in brass frames,
in order to reduce them to the normal temperature, 32. It has been
computed from the following formula:
T m(*-32) s-62)
Corrects -ft-^-^-i^-
ill which
7t=reading of the barometer,
<=temperature of attached thermometer,
w=rexpansion of mercury for 1 F., taken as .0001010 of its length at 32,
s=expansion of the substance of which the scale is made ; for brass is taken
as .00001020 of its length (/t) at the standard temperature for the scale*
viz: 62 F.
CORRECTION FOR ALTITUDE OR REDUCTION TO SEA LEVEL.
As we ascend in the atmosphere the pressure gradually diminishes-
At the height of Pike's Peak, 14,134 feet above sea level, the mean
pressure is about 17.8 inches. At sea level it is 30.0 inches.* In
order then to make barometer readings comparable at different
stations it is necessary to reduce them to a common plane. This
is taken as sea level. This reduction depends upon the temper-
ature of the outside air as well as the height of the station. It is
important that each observer obtain as accurately as possible
the elevation of his barometer, first, above a fixed point near its place
*A convenient rule for finding the difference of level between two places by means
of barometer observations is as follows: The difference of level in feet is equal to the
difference in pressures at the two places divided by the sum of the pressures and mul-
tiplied by the number 55761 for a mean temperature of the air at the places equal to
60 ; for every degree the temperature is greater than 60 the number is 117 greater,
and for every degree below 60 it is 117 less. For example, with the observed pres-
sure of 29.0 inches at a height and 30.0 inches below with the air temperature 60,
the difference of level between the two places is, ^ X 55761 = 945 feet.
40
of suspension ; second, the elevation of the fixed point above some
plane, such as a railroad track at station, bench-mark on canal, or
zero of river gauge, the height of which above sea level is known.
The sum of these three quantities will give the elevation of the
barometer above sea level. If it is found impossible to get the
correct elevation in this way, an approximate value may be com-
puted by means of barometric observations at the station, com-
pared with those made at the same time at a neighboring station,
the elevation of which is known. As a general thing, however,
it will be found feasible to obtain the elevation from a railroad track
near the station. Table VII at the end of these instructions will
give the reduction for barometer readings at stations up to 1,500
feet. For greater heights the pressure at sea level may be com-
puted from the following formula:
From a table of common logarithms, the natural number corresponding to log l f is
found; OT =n, and h=nli /
In this formula
h and /j/=barometer reduced to 32 F., at sea level and upper station, respect-
ively,
t and < / =the temperature of the air at the respective stations,
/^elevation of upper station in feet,
Platitude of the place.
Barometers are standardized by suspending them near a correct
standard barometer and shifting the scale until its reading coincides
exactly with the standard or its correction is derived to reduce to
the standard. The instrument is hung with lower end free. If the
lower end is fixed for convenience in adjusting the mercury in cis-
tern to the ivory point, care must be taken to fasten it without
changing the verticality of the tube. Any changes in the suspend-
ing ring, putting on a heavier attached thermometer, or shifting the
ivory point in cistern, is apt to throw the instrument out of adjust-
ment and cause its readings to be erroneous by several hundredths
of an inch.
To make pressure observations at different latitudes strictly com-
parable, a correction must be introduced for the variation in the
force of gravity on the different parallels from the equator to the
poles. The reduction is made to the latitude of 45 and sea level-
At latitude 30 the correction amounts to 0.039 f an inch; at 70
to -j- 0.060.
Pressures can be observed accurately with a mercurial barometer
of one-quarter inch bore to about 0.006 of an inch. For more
accurate pressures a tube a half inch or inch in diameter is required
with a very elaborate apparatus called a cathetometer, for measur-
ing the difference in level of the surfaces of mercury in cistern and
41
ANEROID BAROMETER.
Fig. ii represents the latest improved form of an aneroid. The
outer casing and face of the instrument are removed, but the
index hand is left attached to the arbor. A is the corrugated
vacuum box which has been exhausted of air through the tube /
and hermetically sealed by soldering. is a powerful curved spring
resting in gudgeons fixed on the base plate, and attached to a
socket behind F, in the top of the
vacuum box. A lever, C, joined to
the stout edge of the spring, is con-
nected by the bent lever at Z>, with
the chain , the other end of which
is coiled round and fastened to the
arbor F. As the box A is compressed
by the weight of the atmosphere
increasing, the spring^, is tightened,
the lever C depressed, and the chain
FIG. 11. E uncoiled from F which is thereby
turned so that the hand If moves to the right. In the meanwhile
the spiral spring G coiled round F, and fixed at one extremity to the
frame work, and by the other to F, is compressed. When, therefore,
the pressure decreases, A and B relax by virtue of their elasticity;
E slackens, G unwinds, turning F, which carries the index hand If
to the left. Near J is shown an iron pillar, cast as part of the stock
of the spring^. A screw works in this pillar through the bottom of
the plate, by means of which the spring B may be so adjusted to the
box A as to set the index H to read on the scale in accordance with
the indications of a mercurial barometer. In the higher class of
aneroid barometers the lever Cis formed of a compound bar of brass
and steel, so arranged as to compensate for the effects of extreme vari-
ations of temperature. A very small movement of the surface of the
vacuum chamber causes a large deviation of the needle end, Q of
an inch causing it to move through a space of 3 inches.
Aneroids have to be graduated with reference to a mercurial
barometer.
The elasticity of a spring varies with temperature. A given weight;
will pull down a spring more at a high temperature than a low one.
This causes an aneroid to read too high with temperature. In the
best forms of aneroid there is an attempt made to compensate for
temperature, by making one of the transmitting levers a compound
of two metals, a strip of steel and brass soldered lengthwise. An
accurate compensation is only rarely accomplished in this way, and
when it is accomplished, in the case of some instruments, it is a mere
accident. To get correct pressures every instrument must be
investigated and corrections for different pressures and temper-
atures derived. A change of 20 in the temperature of the
42
instrument will often change the pressure indication one-tenth of
an inch, in some instruments one way and in others the opposite,
without any actual change going on in the pressure of the air.
A compensation is sometimes attempted by leaving some air in
the box. As the spring weakens at a high temperature the increas-
ing pressure of the air inside the box, due to the higher temperature,
counterbalances the effect on the spring to some extent. This
method of compensation is usually ineffective.
Aneroid barometers do not require a gravity correction, the ten-
sion of a spring not varying with latitude.
The spring of an aneroid barometer changes with age and with
extreme variations of pressure causing its indications to vary inde-
pendently of variations in the pressure, of the atmosphere. There
is a continual rise in the indicated pressures with age of the instru-
ment, amounting, usually, to 0.08 of an inch in three years. After
subjection to a low pressure, as in a mountain ascent, an aneroid
does not recover its original reading at once when restored to
ordinary pressures. After lowering to a pressure of 18 inches its
reading will be 0.3 of an inch lower than it was before when brought
back to a pressure of 30 inches. The original reading is recovered
in a few weeks.
An aneroid requires constant control and adjustment by reference
to a mercurial barometer. It is not as accurate or satisfactory for
making pressure observations as a mercurial instrument. Shocks
and jars are liable to derange it. On account, however, of its conve-
nience, the ease with which it can be carried over rough country
where a mercurial barometer would be liable to be broken, the
aneroid is used a good deal in making observations of pressure,
especially for approximate determinations of altitude. An aneroid
is rarely used in meteorological observations, usually only when a
mercurial barometer is out of order and until another one can be
procured.
The words "fair," "stormy," "rain," etc., sometimes on the dial
of an aneroid have no real significance as regards weather, being
simply a device intended to help the sale of the instruments.
HYPSOMETER.
The temperature of boiling water is lower, the lower the pressure
of the air. The boiling point at a standard pressure of 29.922 inches
is 2i2.o; at a pressure of 18.0 inches it is i87 .5. This fact is made
use of at times in determining pressures, especially for the deter-
mination of altitudes in mountain ascents.
A thermometer with its boiling point apparatus when used for the
purpose of determining pressures is called a hypsometer. The ther-
mometer is made short, only about 6 inches in length, for convenience
in carrying, and is graduated only from about 170 to 214. The
best form of thermometer for this purpose has two or three degrees
43
in the vicinity of freezing point graduated on the stem to permit of
observations of the variation of the freezing point. An inconvenient
length of stem is avoided by means of an enlargement in the bore
of the stem, between freezing point and the graduation of 170, in
order to hold the mercury.
The pressure observed with a hypsometer can be made with an
accuracy of about 0.06 of an inch.
READING INSTRUMENTS.
In reading thermometers or barometers, it is essential to bring the
eye so that the line from the eye to the end of the column shall be
horizontal. This is most important in case the thermometer is
graduated only on the brass scale behind the tube, as a little varia-
tion in the position of the eye above or below the line of graduation
will make a large difference in the reading. Care should be taken
in the reading to note correctly the number of degrees that the
thermometer indicates. It has been found that frequently errors of
5 creep in from a want of care in this respect. A little practice will
enable any one to split the degree into tenths ; /. e. t to regard the
space as divided into ten equal parts and to take the nearest tenth
that the instrument indicates for record.
RAIN GAUGE.
Rainfall is measured as the depth of water it would form on the
ground were it to remain as it falls. In the case of snow its depth
is measured as the depth of water it would form if melted. Rain,
hail, and snow are known under the general designation of precipi-
tation.
Snowfall is preferably measured as depth of water rather than by
the thickness of layer it forms on the ground. When it is not con-
venient to measure it by melting, it is customary to take it as one-
tenth of the measured depth of the snow on a level open place. The
relation between the depth of snow and depth of melted snow is
very different in different cases, depending on the wetness of the
snow. The equivalent depth of water in some cases is as great as
one-seventh of the depth of snow and in others only one thirty-
fourth. It is always best to melt it for measurement.
Rain-gauges in slightly different positions differ greatly in the
depth of rain indicated. Within a few yards of each other two
gauges may show a difference of 20 per cent, in the rainfall in a
heavy rainstorm. The stronger the wind the greater the difference
is apt to be. In a high location eddies of wind produced by walls
of buildings divert rain that would otherwise fall in the gauge. A
gauge near the edge of the roof, on the windward side of a building,
shows a less rainfall than one in the center of the roof. The verti-
cal ascending current along the side of the wall extends slightly
above the level of the roof, and part of the rain is carried away from
the gauge.
44
In the center of a large flat roof, at least 60 feet square, the rain-
fall collected by a gauge does not differ materially from what is
collected at the level of the ground.
A rain-gauge mounted on a mast at a height of 43 feet collects
only 0.75 as much as at the ground ; at 85 feet, only 0.64 ; and at 194
feet, only 0.58.
A gauge on a plain with a fence 3 feet high around it at a distance
of 3 feet will collect 6 per cent, more rain than without the fence.
These differences are due entirely to wind currents.
Forests intercept from 6 to 15 per cent, of the rainfall in different
rain storms.
INSTRUCTIONS FOR USE OF THE RAIN-GAUGE.
The Weather Bureau solicits the observation and record of rain,
snow, and hail, at carefully selected stations, with a three-fold object:
to benefit commerce on navigable streams, to assist the operations
of agriculture by irrigation and water storage in regions where the
rainfall is insufficient at the time when the crops most require water,
to enable specialists of the bureau to gain such knowledge of the
climate of the several regions of the country as will permit them to
supply engineers and others with the facts which are needed to govern
them in the construction of waterworks and other undertakings.
These eminently practical benefits are to be obtained only by care-
fully prepared records of observations of the rainfall made at many
stations. To secure accuracy each observer should study the in-
structions herewith offered for his guidance.
Each station will be equipped with a standard rain-guage, and, if
possible, a wooden box support, complete, which is to be mounted
in the manner described below.
The rain-gauge consists of three parts
The receiver, A.
The overflow attachment, B.
The measuring tube C.
The top cylindrical portion of the receiver, marked a in Fig. 12, is
exactly 8 inches in diameter inside, and is provided with a funnel-
shaped bottom, which conducts any precipitation falling into the
receiver into the tall cylindrical measuring tube, C, the total height
of which, inside, is exactly 20 inches. The diameter of this tube is
much smaller than the large receiving tube, a, being only 2.53 inches.
In consequence of this a small amount of rain falling into the re-
ceiver and flowing into C fills the latter to a depth greater than the
actual rainfall in proportion as the area of the receiver is greater
than the area of the measuring tube. In the standard gauges of the
Weather Bureau the depth of the rainfall, in accordance with this
principle, is magnified just ten times. The receiver, A, has a sleeve,
</, Fig. 13, which slips over the tube, C, and very effectually prevents
45
any loss of rainfall. Again, when the rainfall is very heavy the
tube, C, may be more than filled. In this case to still prevent loss a
little opening, shown at <?, Fig. 14, is made in the sleeve, d> just on a
level with the top of the tube, C. The excess of rainfall escapes
through this opening, and is retained in the large overflow attach-
ment, B, and can be measured afterwards, as will be described below.
In the drawing the diameter of the overflow attachment is shown as
less than 8 inches, but in the latest style gauges this part is now also
made just 8 inches inside diameter. The object of this is to be able
to use this portion of the instrument as a snow gauge, as will be ex-
plained hereafter.
Fig.lZ.
Front View.
Pig. 13.
Vertical Section.
RAIN GAUGE.
\
--.
f
4
B
?
C
d
3
Receiver.
Fig.15.
Horizontal Section,E-i;
I 234 56 7 Q 9 10 II 12 13 14 IS- 16 17 IB 19 20 21
& \*uu.
SCALE.
EXPOSURE OF RAIN-GAUGES.
It is desired observers use particular care in selecting a good place
of observation, as the value of the records is sometimes greatly im-
paired by improper exposure. It is scarcely necessary to say that
every precaution should be taken to protect gauges from the inter-
ference of animals and unauthorized persons. Select, if possible, a
position in some open lot as unobstructed as possible by trees, build-
ings, or fences. Such a place in general affords the best exposure,
though sometimes difficult to find. Gauges should be exposed upon
roofs of buildings only when necessary, and then the roof should be
flat, or nearly so. The middle portion of a flat unobstructed roof
generally gives the best results.
46
RAIN-GAUGE SUPPORT.
The box in which the gauge is shipped to the observer is expressly
designed as a stand for the instrument, and should be opened at the
head, which is fastened by screws. Set the box up as nearly vertical
as possible at the place selected for the exposure and ballast by fill-
ing the lower portion with several inches of stone or broken brick.
Slip in the head and lower to the level of the screw holes in the sides
of the box about 10 inches from the bottom, where the head is
securely fastened with the screws taken out in opening the box.
The support is further secured and fixed in its position by piling
up a few stones around the outside. The gauge can now be placed
inside and appears as shown in Fig. 16.
Ratn Gauge cutoi Support.
FIG. 16.
TO MEASURE RAINFALL AND SNOWFALL.
Rainfall. The rain-gauge measuring stick is graduated into inches
and tenths of inches. Remembering that the actual depth of the
rainfall is magnified ten times, as explained above, it is plain that
if we find the water 10 inches deep .in the measuring tube, then the
real rainfall must have been only one inch deep, or, if the water in
the tube is only one-tenth inch (or written as a decimal .1 inch) deep,
then the rainfall must have been only one one-hundreth inch (or
written as a decimal .01 inch).
47
To save observers the trouble of always thinking about the mag-
nification, and to avoid possible errors in reports, the numbers on
the graduation of the measuring sticks are not actual inches, but in
the latest pattern of measuring sticks have all been divided by 10,
and thus represent the actual rainfall. Moreover, these numbers
are expressed in hundredths of inches of rainfall, and are written
as decimal fractions. Thus the ten-inch lige is numbered i.oo (read
one and zero hundreths), which is the depth of rainfall in inches
corresponding to i-o inches of water in the measuring tube ; similarly
the one-inch line is numbered .10 (read ten one-hundredths), which
again is the depth of rainfall in inches corresponding to one inch of
water in the tube.
The depth of the water is measured by inserting the measuring
stick into the gauge through the small hole in the funnel. When
the stick reaches the bottom of the measuring tube it should be held
for one or two seconds and then quickly withdrawn and examined
to see at what division of the graduation the top of the wetted por-
tion comes. The numbering of this division as stamped on the stick
gives, as has just been explained, the actual depth of rainfall, and in
making out records and reports observers should always use the decimal
expressions. Of course it will rarely happen that the top of the
wetted portion will fall exactly upon one of the numbered lines it
will generally be on or near one of the shortest lines. Thus, for
example, suppose the water-mark comes to the sixth short line
beyond the line numbered .80, the proper record to make in this case
would be .86 inch rainfall. The number of short lines, reckoned from
the numbered line next lower, are always to be inserted in place of
the o in the stamped numbers.
Observers should always be careful to put the stick into the gauge
so that the end at which the numbering begins goes to the bottom,
and the stick passes through the middle of the tube; for if the stick
is placed near the sides the water is sometimes drawn up by capil-
lary action in the narrow space between the stick and the tube, so as
to wet the former entirely too high and give very erroneous records.
After measuring and recording in this way the water found in
the gauge the top should be removed, the measuring tube emptied
and drained, and the gauge put in position again. Observers should
be careful after emptying the gauge to replace the measuring tube
so that the bottom stands within the ring in the middle of the
bottom of the overflow, and in putting on the receiver that it passes
over the measuring tube and rests squarely down upon the overflow.
When the amount of rain that has fallen more than fills the meas-
uring tube, the total rainfall is determined in the following manner:
First carefully remove the receiver so as not to spill any of the
water in the measuring tube, which should be exactly full; the latter
is then slowly and carefully lifted out so as not to spill any of the
48
water into the overflow, emptied and allowed to drain a moment or
so; the water remaining in the overflow is now poured into the
measuring tube, being careful not to lose any, and measured in the
usual way. Suppose we find this to be .47 inch rainfall, then, re-
membering that the measuring tube is just 20 inches high, the total
rainfall will be 2 inches + .47 inch=2.47 inches.
Snowfall. During the winter season, especially in those climates
where the precipitation^ nearly all in the form of snow, it is neces-
sary to have only the overflow attachment exposed in the support
as a snow-gauge, removing the receiver and measuring tube to the
house, as these parts cannot be used for measuring snow, and even
if rain should occur it is very apt to be frozen while in the measur-
ing tube, generally bursting it and rendering it worthless or highly
inaccurate.
The snowfall collected in the overflow attachment is measured by
first placing the vessel in a warm room until the snow is melted.
The water is then carefully poured into the measuring tube and
measured just as though it were rainfall.
In addition to this measurement by the gauge a measurement will
be made of the actual depth in inches of the snow on the ground.
Select a level place of some extent where the drifting is least pro-
nounced and measure the snow in at least three places. The mean
of these measurements will give the snowfall which is to be entered
in the fourth column of the report, and whenever it is impracticable
to melt the snow as described in the preceding paragraph, one-tenth
of this mean will give an approximate value, in water, for the snow
which could not be melted. This value must be set down in the
third column of the report in precisely the same manner as rainfall,
or snow melted in the gauge. After having once made a measure-
ment of the snowfall it is not desired that the same snow be meas-
ured at each succeeding observation until it shall finally disappear.
Any fresh snow, however, should be measured and recorded as it
falls. If there be any snow on the ground at the middle and end of
the month that fact and the depth in inches should be noted.
Observations should be made every evening, also at the close of
every storm, and the gauge should be emptied of all the water it may
contain as soon as it has been measured.
The form supplied for these records will be found self-explanatory.
Rainfall observers will disregard the columns headed "Tempera-
ture," and confine their attention to those headed " Precipitation."
The first and second columns have to do with the time of beginning
and ending of the storm, and together measure its duration. In
the third column is to be entered the reading of the gauge, as de-
scribed on pages 46 and 47 of these instructions. If no rain,
snow, or hail has fallen during the period of observation make the
entry .00, or "No precipitation," in this column. If the amount is
49
too small to measure make the entry " Trace." The fourth column
is provided for the record of snow measurements made by the
method described on page 48. In the "Monthly Summary" all
matters indicated are proper subjects of the rainfall observer's
record, with the exception of the three lines which deal with tem-
perature.
It is particularly important in the interests of accuracy that the
observations be recorded as soon as made, and that the daily entries
be made day by day. The forms for each month should be mailed
on the first day of the succeeding month. Even if no rain has fallen
the observer should bear in mind that his official record of that fact
is as important as though it were a month of rain.
Requisition for blank forms or envelopes may be made at any
time, and will receive immediate attention. It is not necessary to
write a letter asking for them; a simple note on the margin of the
monthly report will be sufficient.
PERCOLATION GAUGE.
An instrument for measuring the rainfall that reaches different
depths in the earth is a percolation gauge, sometimes called a
lysimeter. It consists of an iron vessel, imbedded in the earth,
three feet in diameter and three feet deep, filled with earth, and the
top surface level with the ground. There is a pump for drawing
off the water that collects in a depression on one side at the bottom
of the vessel, which then has to be measured.
The amount of rainfall that reaches a depth of three feet is only
about one-third or one-fourth of the annual depth of rainfall as
measured at the surface of the ground. It varies a good deal with
the nature of the soil.
WIND VANE.
The wind vane is the instrument by which the direction of the
wind is observed. The direction of the wind is always considered
as the direction from which it is coming. The direction is noted to
the nearest principal point of the compass from which it is blowing,
north, northeast, east, southeast, south, southwest, west, or northwest.
A calm is recorded when there is not sufficient wind to move the
anemometer cups.
The motion of smoke from chimneys can be used to observe the
direction of feeble currents of air, too weak to turn the wind vane.
The Weather Bureau form of wind vane is shown in Fig. 17. The
arrow is about 6 feet long ; the tail piece is of pine 10 inches wide,
split to form an angle 'of about 10. This is considered to
steady the direction of the vane and render it more sensitive to the
action of light currents than if it were a plain board.
The wind vane should be set in as free and open a space as
possible, away from every obstacle, especially high buildings. It
should be 8 or 10 feet above a roof.
Friction. Roller.
Wind Vcvne and, Ceittng Died.
FIG. 17.
51
In the complete form of wind vane there is a rod connecting with
the vane, passing through the support and the roof of building and
attached to an index centered in a dial on the ceiling of a room.
The principal points of the compass are marked on dial, and the
wind direction can be noted without direct observation of the vane.
In noting changes in the direction of wind the terms veering and
backing are used. Veering is a change in the direction from the
north to the northeast, through the east to the southeast, southeast
to south and southwest, etc., corresponding to fhe direction of mo-
tion of the hands of a watch. Backing is changing in the reverse
direction, around by north, through the west, etc.
ANEMOMETER.
The instrument generally used in determining the velocity of the
wind is the Robinson anemometer, shown in Fig. 18.
FIG. 18.
It consists of four hollow hemispherical cups upon cross-arms at
right angles to each other, with the open sections vertical and facing
the same way around the circumference.
The cross-arms are on a vertical axis which has at its lower end
an endless screw. The axis is supported so as to turn with as little
friction as possible. The endless screw is in gear with a wheel
which moves two dials registering the number of revolutions of the
cups.
9377 4
52
The center of the cups moves with a velocity about one-third
that of the wind which puts them in motion.
The cups are 4 inches in diameter. The distance from center of
cup to center of rotation or axis is 6.72 inches. On the assumption
that the wind travel is exactly three times that of the center of cup,
the dials are marked to register miles of wind travel, 500 revolu-
tions of the cups corresponding to a mile.
The ratio of wind travel to travel of cup is in reality variable,
depending on the velocity of the wind. It is less for high than low
velocities. It varies also with the dimensions of the instrument,
being different for every different length of arm and diameter of cup.
The true velocities corresponding to observed velocities areas fol-
lows :
Observed ve- True velocity,
locity, miles miles per
per hour. hour.
10 9.8
20 17. 8
30 25. 7
40 33. 3
50 40. 8
60 48.
70 55. 2
80 62. 2
90 69. 2
The pattern of anemometer used in the Weather Bureau has the
registering dials mounted concentrically. The outer dial has one
hundred and the inner dial ninety-nine divisions. As the dials are
moved by the same wheel, they will move forward one hundred
divisions in the same time (Fig. 19). The outer dial having one
hundred divisions, the inner dial will complete one revolution and
its zero be one division beyond or to the left of the zero of the outer
dial when the outer dial has completed one revolution, the zeros of
the scales coinciding at the time the instrument was set in motion.
Thus the revolutions made by the outer dial are recorded on the
innei- one, the number of revolutions being shown by the number
of divisions of the scale on the inner dial between the zero of that
scale and the zero of the outer one. In taking the reading of the
anemometer at any time, the hundreds and tens of miles are read
from the inner scale and the miles and tenths of miles are read from
the outer one. Take from the inner scale the hundreds and tens of
miles contained between the zero of that scale and the zero of the
outer one, and the miles and tens of miles on the outer scale con-
tained between the zero of that scale and the index of the instru-
ment, and the sum of these readings will be the reading of the
instrument at the time of making the observation.
When the anemometer is not furnished with an index point the
center of the small wheel which gives motion to the dials will be
taken as the reference point.
53
The total movement for the twenty-four hours wil be obtained
in the following manner : Subtract the reading of the anemometer
at 12 noon of the preceding day from the reading taken at 12 noon
of the current day, and the difference will be the total movement of
the wind. When the reading of the anemometer is less than the
reading of the preceding day, 990 miles will be added to it, and the
remainder, after sulitracting the reading of the preceding day, will
be the total movement.
Example : The* dial reading of to-day is 91, and that of yesterday
was 950, hence we have 91 + 990 = 1081 ; 1081 950=131, the total
observed movement of the wind in miles during the past twenty-
four hours.
Anemometers must be kept carefully and thoroughly oiled to
prevent friction and injury to the several bearings. Especial
attention must be given to the large dial-screw, and when found
loosened it must at once be tightened, but care must be taken not
to screw it up tight enough to interfere with the free motion of the
dials.
The pressure of the wind on a surface varies as the square of the
velocity. The pressure in pounds per square foot of vertical expos-
ure of a surface is equal to 0.004 multiplied by the square of the true
wind velocity in miles per hour.
When there is no anemometer for measuring the velocity, the
force of wind is estimated according to a scale of numbers from i to
12. The scale in most common use, especially at sea, is the Beaufort
scale. Estimates on this scale at sea are made for the most part
according to the commotion the wind causes in the water or the
rigging of a ship. This arbitrary scale originated in the days of
sailing vessels. The wind force was indicated by the various num-
bers according to the amount of sail that could be safely carried.
The velocity in miles per hour corresponding to the different num-
bers has been ascertained by comparison of the estimated force on
ships at sea with actual velocities observed by anemometers on
shore in the vicinity at the same time.
The scale is as follows:
Wind force,
Beaufort scale.
Velocity,
miles per hour.
Calm
1
Light air
3
2
Light breeze _
13
3
Gentle breeze
18
4 _
Moderate breeze _ _
23
5
Fresh breeze
28
6
34
7
Moderate gale
40
8
48
9 _
Strong gale
56
10
Whole gale
65
11
Storm
75
12
Hurricane _ _
90
64
The above velocities are not corrected for the errors of anemom-
eter. The velocities are those observed with the English pattern
of anemometer at coast stations in Great Britain. This anemometer
has larger cups and longer arms than the Weather Bureau pattern of
instrument. It is geared and dialed on the supposition that the
FIG. 19. ANEMOMETER DIAL.
wind travel is exactly three times the travel of center of cups. At
30 miles an hour it is probably 2.4 times the velocity of cup instead
of 3.0, as shown by Dohrandt's experiments with specimens of the
instrument at St. Petersburgh, which makes an indicated velocity
of 30 miles correspond to a true velocity of 24.
55
CLOUDS.
There is a very great variety of cloud forms. Seven typical forms
are recognized for meteorological observation according to Howard's
classification.
Cirrus.
Cumulus.
Stratus.
Cirro-cumulus.
Cirro-stratus.
Cumulo-stratus.
Nimbus.
Cirrus. Cirrus cloud, the highest of all clouds, is a streaky, gauzy,
wispy or feathery form of cloud, whitish in color, usually not very
abundant. It forms at great heights, 25,000 to 50,000 feet, rarely
occurring below 16,000 feet. It is sometimes known as "cat's whisk-
ers" and "mares' tails."
Cumulus. Cumulus cloud is masses of compact cloud of a dense
rounded appearance, like cotton bulging from a bale. It has a flat,
horizontal base 3,000 to 5,000 feet above the ground, and towers up
conically to a great height in the sky. Its shape indicates it is the
result of the condensation of moisture as the air in ascending cools
dynamically to the dew point. Cumulus cloud forms the visible
capital of an ascending column of air. It is essentially a day cloud.
It is more common in the afternoon than the morning, and is most
noticeable when the sun is low. It is frequent at all times of the
year.
The distant tall tops of cumulus visible on the horizon at sea are
known as "thunderheads."
Stratus. Stratus cloud is a widely extended sheet of uniform
cloud, named from its resemblance to the regular arrangement of a
stratum of rock or clay. It is a fog lifted up floating in the air. It
is the lowest of all forms of clouds, the height not being more than
1,000 to 2,000 feet. It is essentially a cloud of the night, forming by
radiation of heat from the lower layers of the air.
Cirro-cumulus. Cirro-cumulus is a broken layer of cloud made of
little bunches of whitish cloud, elliptical or elongated patches with
somewhat regular interstices between them without any shading of
light. It is mostly visible near sunset, but always high up in the
sky, at a height of 12,000 to 22,000 feet. It is denser than the cirrus
and of a dark "tone." This is the form of cloud to which the line of
poetry applies:
" The beauteous semblance of a flock at rest."
Cirro-stratus. Cirro-stratus is a thin veil of widely extended cir-
rus. It is a high cloud. At times it is largely composed of ice
particles, as shown by the colored rings seen around the sun and
56
moon viewed through it. Lunar halos are frequent with this form
of cloud.
Cirro-stratus is also at times a condensed and developed form of
cirrus in which the streakiness is very marked, on account of the
great extent of cirrus. At times ribs of cirro-stratus stretch from
a point on the horizon to a point directly opposite. This is an effect
of perspective, the streaks appearing wider apart at the zenith.
This form of cloud is sometimes known as "polar bands." The
stripes or ribs are sometimes made up of cross-bar patches and then
are said to be "striated." The fibres of cirro-stratus sometimes
interlace and have a reticulated appearance like woven cloth.
Cumulo-stratus. Cumulo-stratus is composed of great masses of
dense dark cloud, usually covering the whole sky. It prevails at a
height of 5,000 to 10,000 feet. It is essentially a cloud of the night
and the cold season. The darker forms of cumulo-stratus sometimes
present an unduiatory aspect, especially toward the horizon, an effect
of perspective. This is sometimes called "roll-cumulus." In high
latitudes in winter thick masses of this cloud obscure the sky at
times for weeks.
Nimbus. Nimbus is a dense thick layer of dark cloud, void of shape
or form, without definite edge, and of tattered, ragged outline, from
which rain or snow is continuously falling.
Scud is the small detached scurrying masses of cloud in advance
of and lower down than the main nimbus cloud.
Cloud observations consist in estimating the part of the sky cov-
ered at any time by clouds, the form of the clouds, and their direction
and rate of motion. The form of cloud prevailing indicates some-
thing as to the condition of the upper air; their movement indicates
the direction and rate of motion of the upper currents.
The proportion of sky covered by clouds is determined by inspec-
tion in tenths of the whole visible firmament. A sky wholly over-
cast is recorded as 10; a perfectly clear sky is indicated by o. Only
an approximation to the true amount of sky covered can be made
by estimation. To assist in this estimation it maybe useful to note
that the sky will be divided into 10 equal parts, as regards angular
magnitude as seen by an observer, by lines from five equi-distant
points on the horizon to the zenith and by a horizontal circle at one-
third of the distance from the horizon to the zenith.
Sometimes estimates of cloudiness are made on a scale of o to 4, or
quarters of the sky covered.
The form of cloud is noted which is considered to be the nearest
to one of the forgoing types described. The purely typical forms
are of relatively rare occurrence.
Observation of the direction of motion of the clouds is beset with
great difficulty in most cases, from the fact that the form of cloud
is continually changing, and often from the uniformity of texture it
57
is impossible to identify a point on a cloud for comparison with some
motionless object on the surface of the earth. In the case of clouds
some distance from the zenith, the direction of motion observed must
be made free of the effects of perspective.
CLOUD MOVEMENT. '
The great difficulty in getting at the true direction of cloud move-
ment lies in the effect of perspective. The following device obviates
'this:
" Set up a pointed pole, reaching 6 or 8 feet above the observer's
head, and through the top, an inch or so below the point, fix two
stout cross-wires, or thin iron rods, set truly by compass to the four
cardinal points. The space around the pole must be sufficiently
open to allow of a good view of the sky in all directions. Let the
observer then station himself at such a distance from the pole, and
in such a position that some recognizable portion of a cloud appears to
move vertically upward from the top of the pole or vertically down-
ward toward it. The direction of the pole from the observer's
position (which may be judged of accurately by means of the cross-
wires on the top) is the direction of the cloud's true movement.
With a little care in selecting the position the pole may be dispensed
with, as any pointed object will serve the purpose, provided the
observer has previously acquainted himself accurately with the
points of the compass. The velocity of cloud movement may be
measured in favorable situations by observing the time that the
shadow takes to traverse a certain space of country, the extent of
which is accurately known/'
The direction from which the clouds are moving should be recorded
to 8 points N., NE,, E., etc. The velocity may be recorded by the
letters s (slowly) and r (rapidly) placed as an exponent to the direc-
tion thus, N r , S 8 .
Haze, smoke, and fog should be recorded as such, with the addition
of the words " light " or " dense," as the case may be.
EVAPORATION.
Depth of evaporation in inches from a water surface is measured
by means of an evaporometer or atmometer. A common form con-
sists of a round dish i foot in diameter and 4 inches deep. The
depth of evaporation is ascertained from the loss of weight by means
of weighing at different times. Sometimes this is observed by means
of a graduated scale inside the dish, so arranged that the height of
water surface can be read at any time. Sometimes the scale is
inclined so as to give a magnified reading of the fall of surface.
The vessel is kept in the open air and free from the direct rays of
the sun. Readings of the scale are made daily. The differences of
readings give the depth of evaporation in the intervening time.
58
The dish has to be protected from wind and rain, which interfere
with exact observation.
The Piche evaporometer, shown in Fig. 20, consists of a glass tube
about 9 inches long and 0.4 of an inch internal diameter, closed at
the top and open below, graduated to show equal volumes
contained. It is filled with water and the end covered
with a paper disk 1.2 inches in diameter, held in place by
a metal plate attached to a spring on a slitted brass
collar moving easily along the tube. The water flows
down to the paper, from which it evaporates both on
the upper and under sides. The amount of evaporation
in a given time is obtained by taking the difference in
the readings of the top of the column of water in the
tube.
A paper surface gives off about one-third more water
in a given time than an equal extent of water surface
in a dish.
With a wind velocity of 5 miles an hour the evaporation
is 2.2 times as great as in a calm ; with 10 miles, 3.8;
with 15 miles, 4.9; with 20 miles, 5.7; with 25 miles, 6.1;
with 30 miles, 6.3.
RIVER GAUGE.
A river gauge is a device for measuring the vertical
height of a river surface above some arbitrarily selected
plane, usually at or somewhere near the level of the
lowest water that occurs at the place.
When possible, without too great expense, a river FIG. 20.
gauge is made vertical. It consists of a plank or planks 2 inches
thick and 8 to 12 inches wide, fastened to a bridge pier or piling,
and of sufficient length to cover the greatest range in height of
water ever likely to occur.
The plank is graduated to feet and half feet usually, and the
height of surface of water on it can be read by estimation to the
nearest tenth of a foot.
With the zero of the gauge graduation at or near low water, the
reading of the water surface on the gauge at any time is called the
stage of the river.
When a gauge has to be read on a bridge pier by an observer on
shore at a distance of 50 or TOO feet, in order to render the various
foot and half-foot marks the more conspicuous and legible and
readily recognizable, the gauge is painted in alternate patches or
triangles of black and white, according to some such design as that
shown in Fig. 21.
To prevent obscuring of the foot and half-foot marks by weather-
ing, they are indicated on the plank by rows of copper tacks driven
into the plank.
59
Only the whole foot marks are numbered, and this is likewise
done in copper tacks.
Sometimes a river gauge consists of a strip of the surface of a
stone pier dressed down to a smooth surface so as to receive the
marking and numbering of gauge.
When a river gauge cannot be set vertically on a bridge pier, it
is laid along the bank according to the slope of the ground. It
should then be made of logs or heavy timbers 6
inches by i foot imbedded in the ground, with the
top surface even with the surface of the ground in
the river bank. Strap iron X f an i ncn thick and
2 inches wide is spiked along the top surface, and
[on it are cut the foot marks and intermediate half
foot or tenths of foot marks and the numbering of
the feet showing various heights above the zero of
the gauge. The foot marks on a gauge of this kind
must be accurately located by a civil engineer by
means of a spirit level.
Sometimes a very substantial inclined gauge is
made of lengths of block stone with bars of railroad
iron inlaid, on which the foot marks are cut.
Sometimes a gauge is made of isolated stone piers
buried in the'ground along the bank, the top surface
showing the height in feet above an assumed low-
water plane.
It is not always possible at the time of setting a
gauge to put the zero of the graduation at the exact
level of the lowest water apt to occur.
When a stage of water below the zero occurs, it
is read as a minus stage. It is desirable that the
zero shall be put so low that this will never occur, as
the minus sign is apt to lead to confusion, the same
FIG. 21. numerical stages indicating very different levels of
water, whether plus or minus.
A gauge once established and a long record of readings made, it
is not advisable to ever change the zero of the gauge. It is not
customary to change it, even if there does occur a stage of water
lower than any before known.
For the purpose of ascertaining from time to time any changes
that may occur in the level of the zero of a gauge or any of its
marks, a bench mark is established close by the gauge or somewhere
in its vicinity.
A bench mark consists of some accessible, presumably permanent
point or surface, the difference in level between which and the zero
or some other mark on the gauge is known by actual leveling be-
60
tween the two by means of a spirit level. When this difference is
found to vary it is presumed it indicates a corresponding- change in
the level of the marks of the gauge, requiring adjustment of the
gauge or correction of its readings.
A bench mark is essential in case a river gauge is to be repaired
or renewed, in order to set the new gauge at exactly the same level
as it was before.
On a bridge pier the top surface of the largest stone accessible
in the top course of masonry is often used as a bench mark. Some-
times a bench mark is the top surface of a large stone buried in the
ground especially for the purpose of establishing a permanent
surface. Prominent surfaces in stone buildings are good places for
permanent bench marks. A copper bolt set in the stone wall of
some public building, such as a custom house, post office, or city
hall, is a common -device for a bench mark in a large city.
STATE OF THE WEATHER.
The weather is recorded clear when the sky is -^ - or less obscured;
fair, when the sky is from -fo to ^- obscured; cloudy, when the sky
is more than -$ obscured; light rain (//. r.), when there is light rain;
heavy rain (hy. r.\ when there is heavy rain; in like manner with
light and heavy snow, substituting s for r; fog, haze, smoke, accord-
ing as these are predominant.
FROST.
Occurrence of first and last frost of any growing season should
be specially noted, as well as all killing frosts during the same.
CORONA.
These must be distinguished from halos. Coronae are very common,
especially around the moon, and are produced by the rays passing
through a thin layer of cloud. Sometimes as many as three small
concentric circles may be seen whose diameters are in the ratio of
1:2:3. They are frequently colored, red being the outside color.
These colors are not the pure colors of the spectrum, but rather those
of the opal, and are caused by interference and not refraction. A solar
corona is not often visible on account of the dazzling brightness of
the sun, but it may often be seen by viewing the sun through colored
glass, or noticing its reflection in water.
Halos are large circles of 45 or 90 in diameter. That is, the
diameter is equal to one-eighth or one-fourth the circumference of
the horizon. Both are seldom seen at the same time. The colors
are very feeble, generally approaching whiteness. Halos arise from
the presence in the atmosphere of minute prisms of ice, and are due
to refraction of light. Sometimes the halo is intensified into two
bright spots, one on each side of the central luminary. These are
61
called "parhelia" or " paraselenae " (mock S4ins or mock moons),
sometimes sun-dogs. Still more complicated optical phenomena are
sometimes seen, though rarely, except in high latitudes.
THUNDER STORMS.
Thunder storms six hours apart may be considered as separate
storms.
Upon the occurrence of thunder, give as nearly as possible the
times of first and loudest thunder and duration of thunder (being
careful to note a. m. or p. m. if the hours o to 24. are not used).
Give the direction from which the storm appears to be coming, as
shown by threatening sky, lightning flashes, or thunder peals. Also,
the direction toward which it goes.
TORNADOES AND SAND SPOUTS.
All the meteorological circumstances attending these should be
minutely noted, viz: the course of the barometer, which almost
always sinks much and rapidly; that of the thermometer, which
usually indicates an elevation of temperature; the region of the
heavens in which the thunder storm frequently accompanying them
is formed; the form and color of the clouds; the direction and in-
tensity of the wind; the frequency, intensity, and form of the light-
ning; finally, the apparent shape of the sand-spout, its variations, its
course, and its effects upon the trees and upon the ground, the oc-
currence of hail, etc.
INSTRUCTIONS FOR OBSERVING AURORAS.
Though the aurora borealis has received attention during a con-
siderable portion of the last two centuries, definite information is
still wanting on several points which may serve as the basis of a
sound induction as to its. cause. These relate particularly to the
actual frequency of its appearance; its comparative frequency in
the different months of the year and the different hours of the day;
the connection of its appearance with other atmospherical phenom-
ena; the elevation and extent of visibility of the arch; and whether
the same or different phases are presented to individuals at different
stations at the same moment of time; finally the precise influence of
the arches, streamers, etc., on the magnetic condition of the earth;
and whether any unusual electrical effects can be observed during
the appearance of the meteor.
Auroral phenomena may be divided into the following classes:
1. A faint light in the north, without definite form or boundary.
2. A diffused light, defined by an arch below.
3. Floating patches of luminous haze sometimes striated.
4. One or more arches, of rainbow form, of uniform white color,
62
retaining the same apparent position for a considerable time, and
varying in luminosity.
5. A dark segment appearing tinder the arch.
6. Beams, rays, streamers, waves, transverse and serpentine bands,
interrupted or checkered arches, frequently tinged with color, and
showing rapid changes in form, place, and color.
7. Auroral corona, or a union of beams south of the zenith.
8. Dark clouds accompanying the diffuse light.
9. Sudden appearance of haze over the whole face of the sky.
The following may serve as a scale of brightness: (i) Faint; (2)
Moderate; (3) Bright; (4) Very bright.
GENERAL DIRECTIONS.
1. Make a regular practice of looking for auroras every clear
evening, from 8 to 10 o'clock or later. Record the result, whether
there be an aurora or not.
2. Note the time of observation, and compare the watch used with
a correct clock, as soon after as is convenient.
3. Make a record of the latitude and longitude of the station.
4. Note the class to which the auroral phenomenon belongs.
5. If it be an arch, note the time when the convex side reaches
any remarkable stars, when it passes the zenith, disappears, etc.
6. If the arch be stationary for a time, note its position among
the stars, so that its altitude may be determined.
7. If it be a streamer or beam, note its position, and the time of
its beginning and ending.
8. If motion be observed in the beams, note the direction, whether
vertically or horizontally, to the east or west.
9. Note the time of the formation of a corona, and its position
among the stars.
10. Note the time of the appearance of any black clouds in the
north near the aurora; also, if the sky be suddenly overcast with a
mist at any time during the auroral display.
11. Give the direction and force of the wind at the time.
12. Note if any electrical effects are observed.
13. Note the effect upon a delicately-suspended magnetic needle.
14. The date, hour, and minute of the beginning and ending of
auroras should be carefully noted, as well as the azimuth and alti-
tude of each extremity and of the crown of any arch of light, and
the same data for any corona or glory that may be formed.
When the observer is familiar with the names of the principal
fixed stars, he may locate the arch or crown by reference to them,
but it is preferable that he should observe directly the altitude and
azimuth.
Altitudes are expressed by degrees from the horizon to the zenith.
63
If any circle be divided into three hundred and sixty parts, and
the radial lines connect these parts with the center, each pair of
lines subtends an angle of i; the fourth 'part of the circle will
subtend an angle of 90 or one right angle, and the corresponding
radii are perpendicular to each other; thus the zenith (that point
of the heavens immediately above the observer) is 90 from the
horizon, or, in other words, its altitude is 90. A point halfway up
from the horizon to the zenith has an altitude of 45.
Azimuths are also expressed in degrees, but are measured on the
horizontal plane, and will be recorded, as is done in astronomy, from
the south point to the westward, passing, successively, the west,
north, and east points of the compass until 360 have been passed
over, and the south point is again reached.
Observers should be particular as to the date of the aurora; and
when it begins in the evening of one day and continues into the
early morning of the next day, it will be entered as occurring on
the first day, but its details will be given in the record as occurring
between the hours of its actual beginning and ending. Thus, an
aurora that began on the evening of the i2th of January and con-
tinued until the early morning of the i3th would be entered as the
aurora of the i2th, but its details would be recorded as occurring,
for instance, between the hours of 10 p. m. of January 12 and 2 a. m.
of January 13.
Professor Olmstead, in a paper published by the Smithsonian
Institution, classifies different auroras as follows:
" Class I. This is characterized by the presence of at least three
out of four of the most magnificent varieties of form, namely,
arches, streamers, corona, and waves. The distinct formation of the
corona is the most important characteristic of this class; yet, were
the corona distinctly formed, without auroral arches or waves, or
crimson vapor, it could not be considered as an aurora of the first
class.
" Class II. The combination of two or more of the leading charac-
teristics of the first class, but wanting in others, would serve to
mark class the second. Thus the exhibition of arches and streamers,
both of superior brilliancy, with a corona, while the waves and
crimson columns were wanting, or of streamers with a corona, or of
arches without a corona, without streamers or columns (if such a
case ever occurs), we should designate as an aurora of the second
class.
" Class III. The presence of only one of the more rare character-
istics, either streamers or an arch, or irregular coruscations, but
without the formation of a corona, and with but a moderate degree
of intensity, would denote an aurora of the third class.
" Class IV. In this class we place the most ordinary forms of the
aurora, as a mere northern twilight, or a few streamers, with none
64
of the characteristics that mark the grander exhibitions of the
phenomenon."
The same author remarks:
"On the evening of the 2yth of August, 1827, after a long absence
of any striking exhibition of the aurora borealis, there commenced
a series of these meteors, which increased in frequency and mag-
nificence for the ten following years, arrived at a maximum during
the years 1835, 1836, and 1837, and, after that period, regularly
declined in number and intensity until November, 1848, when the
series appeared to come to a close. The recurrence, however, of
three very remarkable exhibitions in September, 1851, and of another
of the first class as late as February 19, 1852, indicates that the close
was not so abrupt as was at first supposed; but still there was a very
marked decline in the number of great auroras after 1848, and there
has been scarcely one of the higher class since 1853.
EARTHQUAKES.
Immediately upon the occurrence of a shock it is desired that the
observer will collect such information as will enable him to answer
the questions here propounded, and transmit his answers with the
least practical delay to the Weather Bureau office.
If any other reliable information be in his possession, it is desired
that he will communicate it at the same time. It is extremely
desirable that the nearest possible approximation should be made
to the exact time of occurrence, and this should be the first care of
the observer who may feel the shock. If the only time-piece is an
ordinarily good watch or house clock, it would be advisable to com-
pare it with standard time at the earliest practicable moment, which
can now be done at most railway stations.
List of questions to be answered by observers of an earthquake shock.
Station
Date _
1. Was ail earthquake shock felt at your place on the _ day of
, 18 ?
(A negative answer is as important as an affirmative one. )
2. At what hour, minuie, and second of standard time was it felt f
3. How long did its perceptible motion continue ?
4. Was it accompanied by any unusual noise ! If so, describe it
5. Was more than one shock felt j if so- how many ?.
6. Which of the following measures of intensity would best describe what hap-
pened in your vicinity :
No. 1. Very light ; noticed by a few persons ; not generally felt.
No. 2. Light ; felt by the majority of persons ; rattling windows and crockery.
No. 3 Moderate ; sufficient to set suspended objects, chandeliers, etc. , swinging,
or to overthrow light objects.
No. 4. Strong ; sufficient to crack the plaster in houses, or to throw down some
bricks from chimneys.
No. 5. Severe j overthrowing chimneys and injuring the walls of houses.
7. Do you know of any other cause for what happened than earthquake ?
Signature
65
GENERAL PHENOMENA OF CLIMATE.
Information of a general character relating to the growth of
plants will be of value in compiling the climatology of a district.
It is suggested that where voluntary observers can do so the fol-
lowing be included in their records :
Time of plowing in the spring.
Time of planting various crops.
Time of appearance of same above ground.
Time of flowering of strawberries, currants, raspberries, apples,
plums, and other fruit.
Time of commencement of haying.
Time of commencement of harvesting the various cereals.
Time of ripening of various fruits.
Time of first killing frost in fall.
Time of last killing frost in spring.
Time of sowing fall wheat.
Time of appearance of earliest shoots of same above ground.
Time of last snow on ground.
The depth of snow on ground on the last day of each winter
month.
The time of migration of wild fowl and birds, the nights north
and south.
The time of leafing and fall of leaves in deciduous forests.
The date of breaking up of ice in large rivers and bays.
The date of greatest rise and lowest water in important streams.
Voluntary observers are requested to include in their monthly
reports all reliable information relative to the destruction of life
and property coming to their knowledge, due to storms, classifying
it, as far as possible, as indicated in the following table :
I
I
|
it
P,
ill
S'fl
-3
i
0^
1
3
o
t OT3~'o
g'-o'o
*
i
r
i
8
1 I!
slil
if
3
3 o
s s S o
Date of storms.
Nature of ston
northeast gal
Section of coun
by storm.
Number and u
sons killed.
Number and n
sons injured.
Number and n
sels lost or da
estimated am
Number of ho
and other b
stl'oyed or da
estimated am
Estimated amo
age to propei
Number of ani
and estiniatec
66
SPECIAL DIRECTIONS TO THE VOLUNTARY OBSERVERS OF THE
WEATHER BUREAU.
In the reduction of the meteorological records presented to this
office, much additional labor 'has resulted from the occasional omis-
sion in the records of some impoitant facts, and in want of perfect
uniformity in noting the phenomena. To insure uniformity in the
records, attention is called to the following remarks.
1 . Failure to record latitude and longitude, name and station of the observer ,
and date on each sheet, the observer probably supposing it sufficient to
insert them once on the first sheet sent, and so omitting them after-
wards. This often renders it necessary to search back through all
the series of registers to some one that contained them perhaps in
a former year. They should be inserted on every sheet.
2. Designating the same place by different names, thus rendering it
impossible to distinguish whether it is one place or two, unless
by noticing the similarity in the name of the observer or in the
latitude and longitude. Such changes of name should be avoided
when practicable, and when necessarily made, special attention
should be called to it.
3. Diversity in the mode of recording the barometer, as follows :
(a) Integers record in full, thus, 29.35. (THIS is the proper mode.)
() Integers omittted when the same as in the entry next above,
thus, 38.
(c) Integers omitted when the same as in the entry next to the left.
(d) Integers omitted when the same as in the entry next preced-
ing in the order of time.
(e) Integers omitted, except where they are different from the
usual ones at the place of observation.
(/) Integers inserted occasionally and apparently without any
system whatever.
(g) A constant suppressed, and the excess or deficiency recorded,
as + or .
The proper mode is that indicated by (a).
4. Diversity in the mode of recording the thermometer, when it is below
zero, as follows :
(a) Indicated by the sign placed before it, thus, 16.
(This is the proper mode).
(b) Indicated by the same sign placed after it, thus, 16
(c) Indicated by writing it under a zero, thus, - .
(d) Indicated by writing it after a zero, with a comma between,
thus, 0,1 6,
(e) Indicated by the word "below," or the abbreviation b written
before or after it, thus, 16 below, i6b, b 16, or below 16.
The first (a) is the proper mode.
9377 5 67
68
5. Departure from the printed instructions in recording the degree of cloudi-
ness, some observers reversing the figures and using 10 to denote a
clear sky, and o, one entirely overcast; and others omitting the
record altogether in the columns of cloudiness when the sky is clear,
and in place of it sometimes inserting the word " clear " in the columns
of "remarks," or elsewhere. Both lead to error, and -should be
avoided; the zero should always be inserted "in the narrow column,"
as directed, when the sky is clear.
6. Diversity in the use of the character (0) in recording the motion of the
clouds, as follows:
(a) Used to signify a calm, or that there is no perceptible motion.
(This is the correct use].
(b) Used to signify that the sky is clear, instead of inserting it in
the proper column.
(c) Used to signify that no observation was taken.
(d) Used to signify that the direction in which the upper current
was moving could not be determined on account of the sky
being either perfectly clear or entirely overcast.
The first (a) is the correct use.
7. Want of full and proper records of the direction of the wind, some
observers recording the direction only after each change, and then
omitting it so long as it continues the same, merely inserting a figure
to denote the force. It is better to make the record in full. Other
observers record the direction toward which the wind or clouds are
moving instead of indicating that from which they come. A WIND
from the north, or CLOUDS moving from the north, are to be denoted
by N, and from the south by S, etc.
8. Different kinds of thermometers or different exposures used for the dry
and wet bulb thermometers, so that the observations are not comparable
readily, if at all.
9. Diversity in the use of the dash and the sign ("), as follows:
(a) To signify that the entry next above is to be repeated.
(b) To signify that the entry next to the left is to be repeated.
(c) To signify that the entry next preceding in the order of time
is to be repeated.
(d) To signify nothing at all, but merely to fill a blank.
The use of these characters has caused much trouble in the re-
duction, and the true remedy would be to avoid them altogether, by
making each record complete in itself.
10. Illegibility of the records, either from defective chirography or
from being entered in pencil marks and partly erased.
INSTRUCTIONS IN THE USE OF THE TABLES.
TABLE I. DEW POINT.
In Table I are given the temperatures of the dew point as depend-
ent on the reading of the dry and wet bulb thermometers. The
values apply to roof shelters and whirled wet and dry bulb ther-
mometers, but may be used without much error for all shelters well
ventilated. The formula from which the table is derived (Ferrel's)
for dew points below 32 is:
p=p 7 0.000360 P (t t') (14-0-00065 t'), and for dew points above 32:
t t/
pp' 0.000367 P (t t')(i + ), in which,
p= vapor pressure of saturation at the dew point temperature.
p'= vapor pressure of saturation at the wet bulb temperature.
P=barometric pressure taken as 29.4 inches in computing the tables,
t =dry thermometer.
t'=wet thermometer.
Example.
To find the dew point for the reading of the dry bulb 6o.o and
the wet bulb 48.o, entering the table on page 75 with t=6o and
t t' = i2, we find the dew-point 35.
There is a small correction to be applied to the value, if great
accuracy is desired, when the barometric pressure differs from 29.4
inches. This is obtained by the use of Table III, in connection with
Table IV. Having found the dew point, the vapor pressure corre-
sponding to it is taken from Table IV; in the example above for 35
it is 0.203. By means of Table III, with the air pressure, say 27.0
inches, and for the difference of dry and wet bulb 12, the
correction to the vapor pressure is found to be +0.010. The vapor
pressure corrected is then 0.213, an< ^ by Table IV the corresponding
dew point is 36.
TABLE II. RELATIVE HUMIDITY.
In Table II are given the relative humidities corresponding to the
reading of dry and wet bulb thermometers. The relative humidity
of the air at any time is the percentage of moisture contained in the
air as compared with the whole amount it is capable of holding for
the particular temperature at the time. Air containing no moisture
is at zero relative humidity; when saturated the relative humidity
is 100.
Example.
To find the relative humidity for the reading of the dry bulb 6o.o
and the wet-bulb 48.o, entering the table on page 85 with t=6o and
t t'=i2, we find the relative humidity 39 per cent.
70
If it is desired to correct the value for the pressure of 27.0 inches,
the procedure is as follows:
In correcting the dew-point for pressure the corrected value in
example given above was 36. On page 75 in the column for t t' = i2,
the corrected value of 36 is one line lower than the original uncor.
rected value 35. Taking the corresponding value of the relative
humidity in Table II on page 85, one line lower than 39 in the column
for t t'=i2, we have the corrected relative humidity 40 instead of 39.
Tables III and IV are auxiliary to Tables I and II.
TABLE IV.
Table IV gives the vapor pressure at saturation for various tem-
peratures. The values for temperatures above 32 are the Regnault
Broch values; below 32 to 60 they are Marvin's values observed
at the Weather Bureau office, Washington City (see report of Chief
(Signal Officer for the year 1891).
TABLE V. ABSOLUTE HUMIDITY.
Table V gives the weight of vapor contained in the air per cubic
foot of air when saturated at different temperatures.
At a temperature of 43, for instance, when saturated, the weight
of vapor contained is 3.177 grains of water. The weight of vapor
contained in the air at different vapor pressures is nearly propor-
tional to the pressures.
TABLE VI. REDUCTION OF BAROMETER TO 32.
To reduce the barometer reading to the temperature of 32, enter
Table VI with the observed reading and the temperature as shown
by the attached thermometer. For example, suppose the reading is
28.50 and the attached thermometer 73, the reduction is 0.114, or
that amount is to be subtracted from the reading to give the pressure
for the temperature of the instrument at 32,
The reduction is additive below 29 and subtractive above.
TABLE VII. REDUCTION OF BAROMETER TO SEA LEVEL.
Table VII gives the approximate reduction to be applied to an
observation of pressure to reduce it to sea level. The following
example will show its use: Suppose the height of the station is 670
feet, and the temperature of the outside air obtained from the dry bulb
thermometer at the time of the observation is 45, then the reduction
would be .737 or .74; this amount is to be added to the observed ba-
rometer reading to reduce it to sea level. In using the table, observ-
ers should construct one in manuscript, after learning the height of
the station; this should be carried out to every degree of air tem-
perature for the height of the station as found in the left-hand
column.
71
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
^
Difference between the dry and wet thermometers (t t').
JS
t
0.2
0.4
0.6
0.8
to.0
10.2
10.4
10.6
10.8
2.0
20.2
2.4
20.6
b
40
52
9
(t-f)
40
39
50
~
39
38
37
49
48
001
0.2
38
37
36
46
"*
36
35
44
50
60
35
34
43
58
49
58
-34
33
42
55
48
56
33
32
40
52
47
54
32
-31
38
49
46
53
31
30
36
47
45
51
30
29
35
44
44
50
60
28
33
42
56
43
49
58
28
27
32
-40 -52
42
48
56
27
26
30
-37
48
-41
-46
54
26
25
29
35
-45
40
45
52
25
24
23
-28 | -34
27 32
43
40
58
53
39
38
44
43
50
-49
24
23
22
26 ! 30
37
49
-37
42
48
22
21
25 29
35
45
36
41
46
21
20
23 28
33
41
55
35
39
44
20
19
18
-22
21
26
25
31
29
38
35
50
45
34
33
38
37
43
42
19
18
17
<20
23
27
3-2
41
55
32
35
40
17
16
19
22
26
30
37
49
31
34
38
16
15
14
17
16
20
19
24
22
-28
-26
-34
31
44
39
52
30
33
36
15
14
13
12
15
14
18
17
21
20
25
23
29
27
35
:tt
46
41
55
-13
12
11
13
16
18
21
25
30
36
48
11
10
g
12
11
14
13
17
15
20
18
23
21
27
25
33
30
42
37
58
48
10
9
8
- 7
6
10
9
8
12
11
10
14
-13
12
17
15
14
20
18
16
23
*>"!
19
27
25
-23
33
30
27
42
36
32
58
48
41
56
8
- 7
6
K
7
8
10
12
15
17
21
24
29
35
47
5
7
9
11
13
16
19
22
26
31
39
54
4
~~
4
g
8
10
12
14
17
20
23
28
33
44
8
3
5
6
8
10
12
15
18
21
24
29
36
48
2
L
i
2
4
5
7
9
11
13
16
18
22
26
31
39
1
1
3
4
6
7
9
11
14
16
19
-23
27
33
+ i
1
1 1
2
1
3
2
4
3
6
5
8
6
10
8
12
10
14
12
17
15
20
17
24
21
28
25
+ 1
-
1
2
3
. 5
_ 7
8
10
13
15
-18
21
3
4
3
+ l
+ 2
1
2
4
5
7
9
11
13
16
19
4
5
4
3
+ 1
1
2
4
5
7
9
11
14
12
16
14
5
6
6
7
5
g
4
5
3
4
+ 1
3
+ l
1
3
4
6
8
10
12
7
g
7
6
5
4
3
+ 1
1
3
4
6
8
10
8
9
8
7
6
5
4
3
+ 1
- 1
3
4
6
8
9
10
9
8
7
6
5
4
3
+ 1
1
3
4
6
10
11
10
9
8
7
6
5
4
3
+ 2
1
3
4
11
12
11
10
9
9
8
7
5
4
3
+ 2
- 1
2
12
13
12
11
11
10
9
8
7
6
5
3
+ 2
+ 1
1
13
14
13
12
12
11
10
9
8
7
6
5
4
2
+ 1
14
15
14
13
13
12
11
10
9
8
7
6
5
4
3
15
16
15
15
14
13
12
11
10
10
9
8
7
5
4
16
17
16
16
15
14
13
12
12
11
10
9
8
7
6
17
18
17
17
16
15
14
14
13
12
11
10
9
8
7
18
19
18
18
17
16
15
15
14
13
12
11
10
10
9
19
20
19
19
18
17
17
16
15
14
13
13
12
11
10
20
t.
0.2
0.4
0.6
0.8
10
10.2
10.4
10.6
10.8
2.0
2. 2
2.4
2. 6
t.
Point.
72
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
k
0"
Difference between the dry and wet thermometers (tf).
*
I
2. 6
2. 8
3.0
3. 2
3. 4
3. 6
3. 8
4.0
4. 2
4. 4
fc
g,
2
48
2
1
39
54
1
33
43
+ 1
28
35
-46
+ 1
I 2
25
30
37
50
2
3
21
26
31
39
54
3
4
19
22
27
32
42
60
4
5
16
19
23
28
34
45
5
G
14
17
20
24
29
35
47
6
7
12
14
17
20
24
29
37
50
7
8
10
12
15
17
21
25
30
38
53
8
9
8
10
-12
15
18
21
25
31
39
55
9
10
6
8
10
12
15
18
21
26
^31
40
10
11
_ 4
6
8
10
12
15
18
21
26
31
11
12
2
4
6
8
-10
12
15
18
21
26
12
13
_ 1
2
4
5
7
9
12
14
17
21
13
14
+ 1
2
3
5
7
9
11
14
17
14
15
3
+ 1
2
3
5
7
9
11
14
15
16
4
3
+ 2
1
3
4
6
8
10
16
17
6
5
3
+ 2
+ 1
1
2
_ 4
6
8
17
18
7
6
5
4
2
+ 1
2
3
5
18
19
9
8
7
5
4
3
+ 1
l
3
19
20
10
9
8
7
6
5
3
+ 2
+ 1
1
20
t.
2.G
2. 8
3.0
3. 2
3. 4
3. 6
3. 8
4.0
4. 2
4. 4
t.
t.
4. 6
4. 8
5.0
5. 2
5. 4
5. 6
5. 8
6.
G.2
G.4
t.
8
8
9
9
10
57
10
11
41
60
11
12
31
41
59
12
13
-25
31
40
58
13
14
20
25
30
39
56
14
15
16
20
24
30
38
53
15
16
13
16
19
23
28
36
50
16
17
10
12
-15
18
22
27
34
47
17
18
7
9
[2
14
17
21
26
32
44
18
19
- 5
7
9
11
14
17
20
25
30
40
19
20
2
4
6
8
10
13
16
19
is
29
20
t.
4. 6
4. 8
5.0
5. 2
5. 4
5. 6
5. 8
6.0
6. 2
6. 4
t.
73
TABLE I Temperature of the dew point, in degrees Fahrenheit.
1
1
Difference between the dry and wet thermometers (t t').
t
(Dry ther.)
0.5
1.0
1.5
2.0
2. 5
3.0
3. 5
4.0
4. 5
5.0
5. 5
6.0
20
18
17
15
13
10
8
5
2
2
6
-12
19
20
21
19
18
16
14
12
9
7
4
4
8
15
21
22
20
19
17
15
13
11
8
6
+2
1
6
11
22
23
22
20
18
16
14
12
10
7
4
+1
3
8
23
24
23
21
19
18
16
14
11
9
6
3
1
5
24
25
24
22
21
19
17
15
13
11
8
5
+ 2
2
26
26
25
23
22
20
18
16
14
12
10
7
4
26
27
26
24
23
21
20
18
16
14
11
9
6
+ 3
27
28
27
25
24
22
21
19
17
15
13
11
8
5
28
29
28
26
25
24
22
20
19
17
14
12
10
7
29
30
29
27
26
25
23
22
20
18
16
14
11
9
30
31
30
29
27
26
24
23
21
19
18
15
13
11
31
32
31
30
28
27
26
24
22
21
19
17
15
13
32
33
31
31
29
28
26
25
23
22
19
18
16
14
33
34
32
32
30
29
27
26
24
24
21
20
18
16
34
35
33
32
31
30
29
28
26
25
23
22
20
18
35
36
35
34
32
31
30
29
27
26
24
23
21
19
36
37
36
35
33
32
31
30
28
27
26
24
22
21
37
38
37
36
34
33
32
31
30
28
27
26
24
22
38
39
38
37
35
34
33
32
30
29
28
27
25
24
39
40
39
38
36
35
34
33
31
30
29
28
26
25
40
41
40
39
37
3(5
35
34
32
32
30
29
28
26
41
42
41
40
39
38
36
35
34
33
31
30
29
27
42
43
42
41
40
39
37
36
35
34
32
31
30
29
43
44
43
42
41
40
38
37
36
35
33
32
31
30
44
45
44
43
42
41
40
39
37
36
34
33
32
31
45
46
47
45
46
44
45
43
44
42
43
41
42
40
41
38
40
37
39
36
37
35
36
33
34
32
33
t?
48
47
46
45
44
43
42
41
40
38
37
36
35
48
49
48
47
46
45
44
43
42
41
39
38
a7
36
49
50
49
48
47
46
45
44
43
42
41
40
38
37
50
51
. 50
49
48
47
46
45
44
43
42
41
39
38
51
52
51
50
49
48
47
46
45
44
43
42
41
40
52
53
52
51
50
49
48
47
46
45
44
43
42
41
53
54
53
52
51
50
50
49
47
46
45
44
43
42
54
55
54
53
53
52
51
50
49
48
47
46
44
43
55
56
55
54
54
53
52
51
50
49
48
47
45
44
56
57
56
55
55
54
53
52
51
50
49
48
47
46
57
58
57
56
56
55
54
53
52
51
50
49
48
47
58
59
58
57
57
56
55
54
53
52
51
50
49
48
59
60
59
58
58
57
56
55
54
53
52
51
50
49
60
61
60
59
59
58
57
56
55
54
53
52
51
50
61
62
61
60
60
59
58
57
56
55
54
53
52
52
62
63
62
61
61
60
59
58
57
56
55
55
54
53
63
64
63
62
62
61
60
59
58
57
56
56
55
54
64
65
04
63
63
62
61
60
59
59
58
57
56
55
65
66
65
64
64
63
62
61
60
60
59
58
57
56
66
67
67
615
65
64
63
62
61
61
60
59
58
57
67
68
68
67
66
65
64
63
62
62
61
60
59
58
68
69
69
68
67
66
65
64
63
63
62
61
60
59
69
70
70
69
68
67
67
66
65
64
63
62
61
61
70
71
71
70
69
68
68
67
66
65
64
63
62
62
71
72
72
71
70
69
69
68
67
66
65
64
63
63
72
73
73
72
71
70
70
69
68
67
66
66
65
64
73
74
74
73
72
71
71
70
69
68
67
67
66
65
74
75
75
74
73
72
72
71
70
69
68
68
67
66
75
70
76
75
74
73
73
72
71
70
69
69
68
67
76
77
77
76
75
74
74
73
72
71-
70
70
69
68
77
78
78
77
76
75
75
74
73
72
71
71
70
69
78
79
79
78
77
76
76
75
74
73
72
72
71
70
79
80
80
79
78
77
77
76
75
74
73
73
72
72
80
t.
0.5
1.0
1.5
2.0
2. 5
3.0
3. 5
4.0
40.5
5.0
5.5
6.0
<.
74
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
t
(Dry ther.)
Difference between the dry and wet thermometers (< t').
t
(Dry ther.)
6.0
6 3 .5
7.0
7. 5
8.0
8. 5
9.0
9. 5
10.
10. 5
11.
11. 5
12.
19
25
19
20
19
32
20
21
15
24
-47
21
22
-11
19
-31
22
23
8
14
-24
45
23
24
5
-10
-18
30
24
25
- 2
7
-13
22
42
25
26
4
9
-17
28
26
27
+ 3
1
- 6
-12
-20
37
27
28
5
+ 1
O
8
15
25
54
28
29
7
4
4
-10
-18
-32
29
30
9
6
+ 2
- 2
6
-13
-22
43
30
31
11
8
5
+ 1
3
8
-15
-27
31
32
13
10
7
4
4
10
-18
33
32
33
14
12
9
6
+ 3
1
6
-12
-22
44
33
34
16
14
11
8
6
+ 2
2
Q
-15
-27
34
35
18
15
13
10
8
5
+ 1
- 4
- 9
18
32
35
36
19
17
15
12
10
8
4
5
12
-20
42
36
37
21
19
17
14
12
9
6
+ 3
- 2
6
14
-25
-52
37
38
22
20
19
16
14
11
9
6
+ 2
2
8
-16
-29
38
39
24
22
20
18
16
14
11
8
5
+ 1
A
-10
-18
3U
40
25
23
22
20
18
16
13
11
8
4
- 5
-12
40
41
20
25
23
21
20
17
15
13
10
7
+ 4
1
6
41
42
27
26
24
23
21
19
18
15
12
10
7
+ 3
- 2
42
43
29
27
26
24
23
21
19
17
14
12
9
6
+ 2
43
44
30
28
27
20
24
22
20
18
16
14
12
9
6
44
45
31
30
28
27
25
24
22
20
IS
16
13
11
8
45
46
32
31
30
28
27
25
24
22
20
18
16
13
11
46
47
33
32
31
29
28
26
25
23
22
20
18
15
13
47
48
35
33
32
30
29
28
26
25
23
21
20
17
15
48
49
36
34
33
32
31
29
28
26
25
23
21
19
17
49
50
37
35
34
33
32
31
29
28
26
24
23
21
19
50
51
38
37
36
34
33
32
31
29
28
26
24
22
21
51
52
40
38
37
36
34
33
32
30
29
28
20
24
23
52
53
41
39
38
37
36
34
33
32
30
29
28
20
24
53
54
42
41
40
39
37
36
34
33
32
30
29
27
26
54
55
43
42
41
40
39
37
36
34
33
32
30
29
28
55
50
44
43
42
41
40
39
37
36
34
33
32
30
29
56
57
46
45
44
42
41
40
39
37
36
35
33
32
30
57
58
47
46
45
44
42
41
40
39
37
36
35
33
32
58
59
48
47
40
45
44
43
41
40
39
38
36
35
33
59
60
49
48
47
46
45
44
43
41
40
39
38
36
35
60
61
50
49
48
47
40
45
44
43
42
41
39
38
36
01
62
52
51
50
49
48
47
45
44
43
42
41
39
38
62
63
53
52
51
50
49
48
47
45
44
43
42
41
39
63
64
54
53
52
51
50
49
48
47
46
45
43
42
41
64
65
55
54
53
52
51
50
49
48
47
46
45
43
42
65
66
56
55
54
53
52
51
50
49
48
47
46
45
44
66
67
57
56
55
55
54
53
52
51
50
48
47
46
45
67
68
58
57
57
56
55
54
53
52
51
50
49
47
46
68
69
59
58
58
57
56
55
54
53
52
51
50
49
48
69
70
Gl
60
59
58
57
56
55
54
53
52
51
50
49
70
71
62
61
60
59
58
57
56
55
55
54
53
52
51
71
72
63
62
61
60
59
59
58
57
56
55
54
53
52
72
73
64
63
62
62
61
60
59
58
57
56
55
54
53
73
74
65
64
63
63
62
61
60
59
58
57
56
55
54
74
75
66
65
64
64
63
62
61
60
59
58
57
56
56
75
76
67
66
65
65
64
63
62
61
61
60
59
58
57
76
77
68
67
67
66
65
64
63
62
62
61
60
59
58
77
78
69
68
68
67
66
66
65
64
63
62
61
60
59
78
79
70
69
69
68
67
67
GO
65
64
63
62
61
61
79
80
72
71
70
09
68
68
67
66
05
64
63
62
62
80
t.
6.0
6. 5
7.0
7. 5
8.0
8. 5
9.0
9. 5
10.
10. 5
11.
11. 5
12.
/.
75
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
B
M
>-,
Difference between the dry and wet thermometers (t t?).
h
d
"|
12.
12. 5
13.
13. 5
14.
14. 5
15.
15. 5
16.
16. 5
17.
17. 5
18.
40
12
-22
44
40
41
- 6
13
25
41
42
2
n
15
28
42
43
+ 2
3
8
17
33
43
44
6
+ 1
4
10
19
40
44
45
8
5
4
11
22
48
45
46
11
8
+ *
5
13
-24
46
47
13
10
7
+ 3
1
6
14
27
47
48
15
12
10
6
+ 2
2
8
16
30
48
49
17
14
12
9
6
+ 2
3
9
-18
35
49
50
19
16
14
12
9
5
+ 1
4
10
20
42
50
51
21
18
17
14
11
8
5
5
12
22
52
51
52
23
21
19
16
U
11
8
+ 4
6
13
25
52
53
24
22
20
18
16
14
11
8
+ 4
1
6
14
28
53
54
26
24
22
20
18
16
13
10
7
+ 3
2
8
16
54
55
28
26
24
22
20
18
16
13
10
7
+ 3
2
8
55
56
29
27
26
24
22
20
18
15
13
10
6
+ 2
. 2
56
57
30
29
28
26
24
22
20
18
15
13
10
6
+ 2
57
58
32
30
29
27
26
24
22
20
18
15
12
9
6
68
59
33
32
31
29
27
26
24
22
20
18
15
12
9
59
60
35
33
32
30
29
27
26
24
22
20
18
15
12
60
61
36
35
33
32
31
29
28
26
24
22
20
18
15
61
62
38
37
35
34
32
31
29
28
26
24
22
20
18
62
63
39
38
37
35
34
32
31
29
28
26
24
22
20
63
64
41
39
38
37
35
34
32
31
29
28
26
24
22
64
65
42
41
40
38
37
35
34
32
31
29
28
26
24
65
66
44
43
41
40
38
37
35
34
32
31
30
28
' 26
66
67
45
44
43
41
40
39
37
36
34
32
31
30
28
67
68
46
45
44
43
42
40
39
38
36
34
33
31
30
68
69
48
47
46
45
43
42
40
39
38
36
34
33
32
69
70
49
48
47
46
45
43
42
41
39
38
36
35
33
70
71
51
49
48
47
46
45
43
42
41
39
38
36
35
71
72
52
51
50
49
47
46
45
44
43
41
40
38
37
72
73
53
52
51
50
49
48
46
45
44
43
41
40
38
73
74
54
53
52
51
50
49
48
47
45
44
43
41
40
74
75
56
55
54
53
52
50
49
48
47
45
44
43
42
75
76
57
56
55
54
53
52
50
49
48
47
46
45
43
76
77
58
57
56
55
54
53
52
51
50
4!)
48
46
45
77
78
59
58
57
56
55
54
53
52
51
50
49
48
47
78
79
61
60
59
58
57
56
55
54
53
52
51
49
48
79
80
62
61
60
59
58
57
56 55
54
53
52
51
50
80
t.
12.
12. 5
13.
13. 5
14.
14. 5
15.
15. 5
16.
16. 5
17.
17. 5
18.
I.
76
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
t
(Dryther.)
Difference between the dry and wet thermometers (t t').
2
>->
Q_
18.0
19.0
20.0
21.0
22.
23.0
24.0
25.0
26.0
27.0
28.0
29.0
30.
55
-8
55
66
2
19
56
57
+2
10
48
57
58
6
3
22
58
59
9
+ 1
12
59
60
12
5
5
-25
60
61
15
9
14
61
62
18
12
4- 5
6
28
62
68
20
15
9
14
63
64
22
18
12
+ 4
6
32
64
65
24
20
15
9
16
65
66
26
22
18
12
-1- 4
7
34
66
67
28
24
20
15
9
1
-16
67
68
30
26
23
18
12
+ 4
7
37
68
69
32
28
25
20
15
8
17
69
70
33
30
27
23
19
12
+ 5
7
39
70
71
35
32
29
25
21
16
9
17
71
72
37
33
31
27
- 23
18
13
+ 5
6
39
72
73
38
35
32
29
25
21
16
10
16
73
74
40
37
34
31
28
24
19
13
+ 6
6
37
74
75
42
39
36
32
30
26
22
16
10
16
75
76
43
41
38
34
32
28
24
20
14
+ 6
G
34
76
77
45
42
40
36
33
30
26
22
17
11
+ 1
14
77
78
47
44
41
38
35
32
28
24
20
14
7
4
30
78
79
48
46
43
40
37
34
31
27
23
18
11
+ 2
13
79
80
50
47
45
42
39
36
32
29
25
21
15
8
3
80
t.
18.0
19.0
20.0
21.
22.0
23
24.0
25.0
26.
27.
28.0
29.0
30.
t.
77
TABLE I. Temperature of the deiv point, in degrees Fahrenheit.
J
Difference between the dry and wet thermometers (tr-t f ).
I
b
a
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.
11.0
12.0
1
80
79
77
76
74
73
72
70
68
67
65
63
62
80
81
80
78
77
75
74
73
71
70
68
66
6.5
63
81
82
81
79
78
77
75
74
72
71
69
68
66
64
82
83
82
80
79
78
76
75
73
72
70
69
67
65
83
84
83
81
80
79
77
76
74
73
71
70
68
67
84
85
84
82
81
80
78
77
75
74
72
71
69
68
85
86
85
83
82
81
79
78
76
75
73
72
71
69
86
87
86
84
83
82
80
79
78
76
74
73
72
70
87
88
87
85
84
83
81
80
79
77
75
74
73
71
88
89
88
86
85
84
82
81
80
78
76
76
74
72
89
90
89
87
86
85
84
82
81
79
78
77
75
74
90
91
90
88
87
86
85
83
82
80
79
78
76
75
91
92
91
89
88
87
86
84
83
82
80
79
77
76
92
93
92
91
89
88
87
85
84
83
81
80
78
77
93
94
93
92
90
89
88
86
85
84
82
81
80
78
94
95
94
93
91
90
89
87
86
85
83
82
81
79
95
96
95
94
92
91
90
88
87
86
84
83
82
80
96
97
96
95
93
92
91
90
88
87
86
84
83
81
97
98
97
96
94
93
92
91
89
88
87
85
84
83
98
99
98
97
95
94
93
92
90
89
88
86
85
84
99
100
99
98
96
95
94
93
91
90
89
87
86
85
100
101
100
99
97
96
95
94
92
91
90
88
87
86
101
102
101
100
98
97
96
95
93
92
91
90
88
87
102
103
102
101
99
98
97
96
94
93
92
91
89
88
103
104
103
102
100
99
98
97
96
94
93
92
90
89
104
105
104
103
101
100
99
98
97
95
94
93
91
90
105
106
105
104
102
101
100
99
98
96
95
94
93
91
106
107
106
105
103
102
101
100
99
97
96
95
94
92
107
108
107
106
104
103
102
101
100
98
97
96
95
93
108
109
108
107
105
104
103
102
101
99
98
97
96
94
109
110
109
108
107
105
104
.103
102
101
99
98
97
96
110
111
110
109
108
106
105
104
103
102
100
99
98
97
111
112
111
110 109
107
106
105
104
103
101
100
99
98
112
113
112
111
110
108
107
106
105
104
102
101
100
99
113
114
113
112
111
109
108
107
106
105
103
102
101
100
114
115
114
113
112
110
109
108
107
106
105
103
102
101
115
116
115
114
113
111
110
109
108
107
106
104
103
102
116
117
116
115
114
112
111
110
109
108
107
105
104
103
117
118
117
116
115
113
112
111
110
109
108
106
105
104
118
119
118
117
116
114
113
112
111
110
109
107
106
105
119
120
119
118
117
115
114
113
112
111
110
108
107
106
120
121
120 119
118
117
115
114
113
112
111
110
108
107
121
122
121
120
119
118
116
115
114
113
112
111
109
108
122
123
122
121
120
119
117
116
115
114
113
112
110
109
123
124
123
122
121
120
118
117
116
115
114
113
111
110
124
125
124
123
122
121
119
118
117
116
115
114
112
111
1-25
126
125
124
123
122
120
119
118
117
116
115
114
112
126
127
r/6
125
124
123
121
120
119
118
117
116
115
113
127
128
127
126
125
124
122
121
120
119
118
117
116
114
128
129
128
127
126
125
123
122
121
120
119
118
117
115
129
130
129
128
127
126
124
123
122
121
120
119
118
117
130
131
130
129
128
127
125
124
123
122
121
120
119
118
131
132
131
130
129
128
126
125
124
123
122
121
120
119
132
133
132
131
130
129
128
126 ' 125 124
123
122
121
120
133
134
133
132
131
130
129
127
126
125
124
123
122
121
134
135
134
133
132
131
130
128
127
126
125
124
123
122
135
136
135
134
133
132
131
129
128
127
126
125
124
123
136
137
136
135
134
133
132
130
129
128
127
126
125
124
137
138
137
136
135
134
133
131
J30
129
128
127
126
125
138
139
138
137
136
135
134
132
131
130
129
128
127
126
139
140
139
138
137
136
135
133
132
131
130
129
128
127
140
t.
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.
12.0
I.
78
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
t .
(Dryther.)
Difference between the dry and wet thermometers (< t').
?
~
I
12.0
13.0
14.0
15.0
16.
17.0
18.0
19.0
20.0
21.0
22.0
23.0
24.0
80
62
60
58
56
54
52
50
47
45
42
39
36
32
80
81
63
61
59
57
55
53
51
49
47
44
41
38
35
81
82
64
62
61
59
57
55
53
50
48
45
43
40
37
82
83
65
64
62
60
58
56
54
52
50
47
44
42
39
83
84
67
65
63
61
59
57
55
53
51
49
46
43
41
84
85
68
66
64
62
61
59
57
55
53
50
48
45
42
85
86
69
67
66
64
62
60
58
56
54
52
49
47
44
86
87
70
68
67
65
63
6 o
59
57
55
53
51
48
46
87
88
71
70
68
66
64
63
61
59
57
55
53
50
48
88
89
72
71
69
67
66
64
62
60
58
56
54
52
49
89
90
74
72
70
69
67
65
63
62
60
58
56
53
51
90
91
75
73
72
70
68
67
65
63
61
59
57
55
53
91
92
76
74
73
71
69
68
66
64
62
60
58
56
54
92
93
77
75
74
72
71
69
67
66
64
62
60
58
66
93
94
78
77
75
73
72
70
69
67
65
63
61
59
57
94
95
79
78
76
75
73
71
70
68
66
64
63
61
59
95
96
80
79
77
76
74
73
71
69
68
66
64
62
60
96
97
81
80
78
77
75
74
72
71
69
67
65
63
61
97
98
83
81
80
78
77
75
73
72
70
68
67
65
63
98
99
84
82
81
79
78
76
75
73
71
70
68
66
64
99
100
85
83
82
80
79
77
76
74
73
71
69
67
66
100
101
86
84
83
82
80
79
77
75
74
72
71
69
67
101
102
87
85
84
83
81
80
78
77
75
73
72
70
68
102
103
88
87
85
84
82
81
79
78
76
75
73
71
70
103
104
89
88
86
85
83
82
81
79
78
76
74
73
71
104
105
90
89
87
86
85
83
82
80
79
77
76
74
72
105
106
91
90
89
87
86
84
83
81
80
78
77
75
74
106
107
92
91
90
88
87
85
84
83
81
80
78
76
75
107
108
93
92
91
89
88
87
85
84
82
81
79
78
76
108
109
94
93
92
90
89
88
86
85
83
2
80
79
77
109
110
96
94
93
92
90
89
87
86
85
83
82
80
79
110
111
97
95
94
93
91
90
89
87
86
84
83
81
80
111
112
98
96
95
94
92
91
90
88
87
85
84
83
81
112
113
99
97
96
95
93
92
91
89
88
87
85
84
82
113
114
100
99
97
96
95
93
92
91
89
88
86
85
83
114
115
101
100
98
97
96
94
93
92
90
89
88
86
85
115
116
102
101
99
98
97
95
94
93
91
90
89
87
86
116
117
103
102
100
99
98
96
95
94
93
91
90
88
87
117
118
104
103
101
100
99
97
96
95
94
92
91
90
88
118
119
105
104
103
101
100
99
97
96
95
93
92
91
89
119
120
106
105
104
102
101
100
99
97
96
95
93
92
90
120
121
107
106
105
103
102
101
100
98
97
96
94
93
92
121
122
108
107
106
105
103
102
101
99
98
97
96
94
93
122
123
109
108
107
106
104
103
102
101
99
98
97
95
94
123
124
110
109
108
107
105
104
103
102
100
99
98
96
95
124
125
111
110
109
108
106
105
104
103
101
100
99
98
96
125
126
112
111
110
109
108
106
105
104
103
101
100
99
97
126
127
113
112
111
110
109
107
106
105
104
102
101
100
98
127
128
114
113
112
111
110
108
107
106
105
103
102
101
100
128
129
115
114
113
112
111
110
108
107
106
105
103
102
101
129
130
117
115
114
113
112
111
109
108
107
106
104
103
102
130
131
118
116
115
114
113
112
110
109
108
107
106
104
103
131
132
119
117
116
115
114
113
112
110
109
108
107
105
104
132
133
120
118
117
116
115
114
113
111
110
109
108
106
105
133
134
121
120
118
117
116
115
114
112
111
110
109
108
106
134
135
122
121
119
118
117
116
115
113
112
111
110
109
107
135
136
123
122
120
119
118
117
116
115
113
112
111
110
108
136
137
124
123
121
120
119
118
117
116
114
113
112
111
110
137
138
125
124
122
121
120
119
118
117
115
114
113
112
111
138
139
126
125
124
122
121
120
119
118
117
115
114
113
112
139
140
127
126
125
123
122
121
120
119
118
116
115
114
113
140
t.
12.
13.0
14.0
15.
16.0
17.0
18.0
19.0
20.0
21.0
22.0
23.0
24.0
i
79
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
I
Difference between the dry and wet thermometers ( t <').
I
1
24.
25.0
26.0
27.
28.0
29.0
30.0
31.0
32.
33.0
34.0
35.0
36.
"I
80
32
29
25
21
15
8
3
27
80
81
35
31
28
24
18
12
+3
11
81
82
37
33
30
26
' 22
16
9
2
-24
82
83
39
35
32
28
24
19
13
+ 5
9
83
84
41
37
34
30
27
22
17
10
-20
84
85
42
39
36
32
29
25
20
14
+ 6
- 7
64
85
86
44
41
38
35
31
28
23
18
11
+ 1
17
86
87
46
43
40
37
33
30
26
21
15
7
5
38
87
88
48
45
42
39
35
32
28
24
19
12
+ 3
13
88
89
49
47
44
41
38
34
31
27
22
16
9
2
28
89
90
51
48
46
43
40
36
32
29
25
20
13
+ *
10
90
91
53
50
47
45
42
38
35
32
28
23
18
10
91
92
54
52
49
46
44
41
37
34
30
26
21
15
+ 7
92
93
56
63
51
48
46
43
39
36
32
29
24
19
12
93
94
57
55
53
50
47
45
42
38
35
31
27
22
16
94
95
59
56
54
52
49
46
44
40
37
33
30
25
20
95
96
60
58
56
53
51
48
46
43
39
36
32
28
24
96
97
61
59
57
55
53
60
47
45
41
38
34
31
26
97
98
63
61
59
57
54
52
49
47
44
40
37
33
29
98
99
64
02
60
58
56
54
51
48
46
43
39
35
32
99
100
66
64
62
60
57
55
53
50
48
46
41
38
34
100
101
67
65
63
61
59
57
54
52
49
4V
44
40
37
101
102
68
66
65
63
61
58
56
54
51
49
46
43
39
102
103
70
68
66
64
62
60
58
55
53
50
48
45
41
103
104
71
69
67
65
63
61
59
57
55
52
50
47
44
104
105
72
"(0
69
67
65
63
61
59
56
54
52
49
' 46
105
106
74
V2
70
68
66
64
62
60
58
56
53
51
48
106
107
75
73
71
VO
68
66
64
62
60
57
55
52
50
107
108
76
74
73
Yl
69
67
65
63
61
59
57
54
52
108
109
77
76
74
72
71
69
67
65
63
61
58
56
54
109
110
79
77
75
74
72
70
68
66
64
62
60
58
55
110
II 1
80
73
77
75
73
71
70
68
66
64
62
59
57
111
112
81
79
78
76
74
73
71
69
67
65
63
61
59
112
113
82
81
79
77
76
74
72
71
69
67
65
63
60
113
114
83
82
80
79
77
75
74
72
70
68
66
64
62
114
115
85
83
82
80
78
77
75
73
72
70
68
66.
64
115
116
86
84
83
81
80
78
76
75
73
71
69
67
65
116
117
87
86
84
82
81
79
78
76
74
72
71
69
67
117
118
88
87
85
84
82
81
79
77
76
74
72
70
68
118
119
89
88
86
85
83
82
80
79
77
75
74
72
70
119
120
90
89
88
86
85
83
82
80
78
77
75
73
71
120
121
92
90
89
87
86
84
83
81
80
78
76
74
73
121
122
93
91
90
89
87
86
84
83
81
79
78
76
74
122
123
94
93
91
90
88
87
85
84
82
81
79
77
75
123
124
96
94
92
91
89
88
87
85
83
82
80
79
77
124
125
96
95
93
92
91
89
88
86
85
83
82
80
78
125
126
97
96
95
93
92
90
89
87
86
84
83
81
80
126
127
98
97
96
94
93
92
90
89
87
86
84
83
81
127
128
100
98
97
96
94
93
91
90
88
87
85
84
82
128
129
101
99
98
97
95
94
93
91
90
88
87
85
84
129
130
131
132
133
134
102
103
104
105
106
101
102
103
104
105
99
100
101
103
104
98
99
100
101
102
97
98
99
100
101
95
96
97
99
100
94
95
96
97
98
92
94
95
96
97
91
92
93
94
96
89
91
92
93
94
88
89
90
92
93
86
88
89
90
91
85
86
87
89
90
130
131
132
133
134
135
136
137
138
139
107
108
110
111
112
106
107
108
109
110
105
106
107
108
109
104
105
106
107
108
102
103
104
106
107
101
102
103
104
105
100
101
102
103
104
98
99
101
102
103
97
98
99
100
101
95
97
98
99
100
94
95
96
98
99
93
94
95
96
97
91
92
94
95
96
135
136
137
138
139
140
113
112
110
109
108
107
105
104
103
101
100
99
97
140
t.
24.
25 .0
26.
27.0
28.0
29.0
30.0
31.0
32.0
33.
34.0
35.0
36.0
t.
TABLE I. Temperature of the dew point, in degrees Fahrenheit.
1
Difference between the dry and wet thermometers, (<<'). -
?
I
36.0
37 -.0
38.0
39.0
40.0
41.
42.0
43.0
44.
450
46.
47.
48.0
b
89
28
89
90
10
90
91
-22
91
92
+ 7
7
16
92
93
12
+ 2
4
93
94
16
8
+ 4
37
94
95
20
13
10
12
95
96
24
15
15
- 1
25
96
97
26
21
19
+ 7
8
97
98
29
25
23
12
+ 2
18
98
99
32
28
26
17
9
4
-42
99
100
34
30
29
21
14
+ 5
12
100
101
37
32
32
24
18
11
25
101
102
39
35
34
27
22
16
+ 7
7
102
103
41
38
34
30
26
20
13
+ 3
16
103
104
44
40
37
32
29
24
18
10
2
-38
104
105
46
43
39
35
31
27
22
15
+ 6
10
105
106
48
45
42
38
34
30
25
20
12
+ 1
-22
106
107
50
47
44
40
37
32
28
24
17
9
5
107
108 '
52
49
46
43
39
35
31
27
21
14
+ 5
-13
108
109
54
51
48
43
42
38
34
30
25
- 19
12
28
109
110
55
53
50
47
44
41
37
33
28
23
17
+ 8
7
110
111
57
54
52
49
46
43
39
35
31
27
21
14
+ 4
111
112
59
56
54
51
48
45
42
38
34
30
25
19
11
112
113
60
58
56
53
50
47
44
41
37
32
28
23
16
113
114
62
60
58
55
52
50
47
43
40
35
31
27
21
114
115
64
62
59
57
54
52
49
46
42
38
34
30
25
115
116
65
63
61
59
56
54
51
43
45
41
37
33
28
116
117
67
65
63
60
58
56
53
50
47
44
40
36
32
117
118
68
66
64
62
60
57
55
52
49
46
43
39
31
118
119
70
68
66
64
61
59
57
54
51
48
45
42
37
119
120
71
69
67
65
63
61
59
56
53
50
47
44
40
120
121
73
71
69
67
65
63
60
58
55
52
50
47
43
121
122
74
72
70
68
66
64
62
60
57
54
52
49
46
122
123
75
74
7-2
70
68
66
64
61
59
56
54
51
48
123
124
77
75
73
71
69
67
65
63
61
58
56
53
50
124
125
78
76
75
73
71
69
67
65
63
60
58
55
52
125
126
80
78
76
74
73
71
69
67
64
62
60
57
54
126
127
81
79
78
76
74
72
70
68
66
64
62
59
56
127
128
82
81
79
77
75
74
72
70
68
65
63
61
58
128
129
84
82
80
79
77
75
73
71
69
67
65
63
60
129
130
85
83
82
80
78
76
75
73
71
69
67
64
62
130
131
86
85
83
81
80
78
76
74
72
70
68
66
64
131
132
87
86
84
83
81
79
78
76
74
72
70
68
66
132
133
89
87
86
84
82
81
79
77
75
73
71
69
67
133
134
90
88
87
85
84
82
80
79
77
75
73
71
69
134
135
91
90
88
87
85
83
82
78
76
75
73
71
135
136
92
91
89
88
86
85
83
81
80
78
76
74
72
136
137
94
92
91
89
88
86
84
83
81
79
78
76
74
137
138
95
93
92
90
89
87
86
84
82
81
79
77
75
138
139
96
95
93
92
90
89
87
85
84
82
80
79
77
139
140
97
96
94
93
91
90
88
87
85
83
82
80
78
140
t.
36.0
37.
38.0
39.0
40.
41.0
42.0
43.
44.
45 .0
46.0
47.
48.0
I.
81
TABLE II. Relative humidity, per cent.
K.
Difference between the dry and wet thermometers (tf).
_i
b
0.2
0.4
0.6
0.8
10.0
10..
10.4
10.6
1. 8
2.0
2. 2
2. 4
2. 6
"i
40
46
~
(<-<')
40
39
49
JT
39
38
51
38
37
54
b
0. 1
0.2
37
36
56
36
35
59
50
51
35
34
61
22
49
54
34
33
63
25
48
57
33 Rela-
32
31
65
67
30
34
47
46
60
62
-3? tivehu-
31 midity.
30
69
38
45
65
30
29
71
42
44
67
33
29
-28
72
45
17
43
69
37
28
27
74
48
22
42
71
40
27
-26
76
51
26
41
72
44
26
-25
77
53
31
40
73
46
25
-24
78
56
34
12
39
74
49
24
-23
79
58
37
16
38
76
51
23
22
80
60
40
20
37
77
54
22
21
81
62
44
25
36
78
56
21
20
82
64
47
29
11
35
79
59
20
19
83
66
49
33
16
34
80
61
19
18
84
68
52
36
20
-33
81
63
18
17
85
70
54
39
24
9
32
83
65
-17
16
86
71
57
43
28
14
31
84
67
16
15
1 A_
86
73
59
46
AQ
32
Q
19
23
10
30
85
69
15
13
88
76
63
T:O
51
OD
39
27
15
13
12
88
77
65
53
42
30
19
7
12
11
89
78
67
56
45
34
23
12
11
10
90
79
68
58
48
37
26
16
5
10
9
90
80
70
60
50
40
30
20
10
9
8
90
81
71
62
52
'43
33
24
14
5
8
7
91
82
73
63
54
45
36
27
18
9
7
6
91
83
74
65
56
48
39
31
22
13
5
6
5
92
83
75
67
58
50
42
34
25
17
9
5
4
92
84
76
68
60
52
45
37
29
21
13
5
4
3
92
85
77
70
62
65
47
40
32
25
17
10
3
2
93
86
78
71
64
57
50
42
35
28
21
14
7
2
1
93
86
79
72
66
59
52
45
38
31
25
18
11
1
93
87
80
74
67
61
54
48
41
35
28
22
15
+ 1
94
87
81
75
69
63
56
50
44
38
32
25
19
+ 1
2
94
88
82
76
70
64
58
52
46
40
35
29
23
2
3
94
88
83
77
71
66
60
54
49
43
37
32
26
3
4
94
89
83
78
73
67
62
56
51
45
40
34
29
4
5
95
89
84
79
74
68
63
58
53
48
42
3.7
32
5
6
95
90
85
80
75
70
65
60
54
50
44
39
34
6
7
95
90
85
80
76
71
66
61
56
51
47
42
37
7
8
95
91
86
81
76
72
67
62
58
53
49
44
39
8
9
96
91
86
82
77
73
68
64
59
55
51
46
42
9
10
96
91
87
83
78
74
69
65
61
57
52
48
44
10
It
96
92
87
83
79
75
71
66
62
58
54
50
46
11
12
90
92
88
84
80
76
72
68
64
60
56
52
48
12
13
96
92
88
84
81
77
73
69
65
61
58
54
50
13
14
96
93
89
85
81
78
74
70
67
63
59
56
52
14
15
96
93
89
86
82
79
75
71
68
64
61
57
54
15
16
97
93
90
8G
83
79
76
73
69
66
62
59
56
16
17
97
93
90
87
83
80
77
74
70
67
64
60
57
17
18
97
94
90
87
84
81
78
74
71
68
65
62
59
18
19
97
94
91
88
84
81
78
75
72
69
66
63
60
19
20
97
94
91
88
85
82
79
76
73
70
67
64
61
20
t.
0.2
0.4
0.6
0.8
1.
,. 2
10.4
P. 6
,0.8
2.0
2.2
2. 4
2. 6
t.
82
TABLE II. Relative humidity, per cent.
I
Difference between the dry and wet thermometers (t <')
p.
2. 6
2. 8
3.0
3. 2
3. 4
3. 6
3. 8
4.0
4. 2
4. 4
1
2
7
2
1
11
4
1
o
15
9
+ 1
19
13
7
-f 1
2
23
17
11
5
2
3
26
20
15
9
4
3
4
29
24
18
13
8
2
4
5
32
27
22
16
11
6
5
6
34
29
25
20
15
10
5
6
7
37
32
28
23
18
13
9
4
7
8
39
35
30
26
21
17
12
8
3
8
9
42
37
33
28
24
20
15
11
7
2
9
10
44
40
35
31
27
23
19
14
10
6
10
11
46
42
38
34
30
26
22
18
14
10
11
12
48
44
40
36
32
28
25
21
17
13
12
13
50
46
42
39
35
31
27
24
20
16
13
14
52
48
45
41
37
34
30
27
23
19
14
15
54
50
47
43
40
36
33
29
26
23
15
16
56
52
49
46
42
39
36
32
29
25
16
17
57
54
51
48
44
41
38
35
31
28
17
18
59
56
53
49
46
43
40
37
34
31
18
19
60
57
54
51
48
45
42
39
36
33
19
20
61
58
56
53
50
47
44
41
38
'35
20
t.
2. 6
2.8
3.0
3. 2
3. 4
3. 6
3. 8
4.0
4. 2
4. 4
t.
t.
4. 6
4. 8
5.0
5. 2
5. 4
5. 6
5. 8
6.0
6. 2
6. 4
t.
8
8
9
9
10
2
10
11
6
2
11
12
9
5
2
12
13
13
9
5
2
13
14
16
12
9
5
2
14
15
19
16
12
9
5
2
15
16
22
19
16
12
9
6
2
16
17
25
22
19
16
12
9
6
3
17
18
28
25
22
19
16
13
9
6
3
18
19
30
27
24
21
19
16
13
10
7
4
19
20
33
30
27
24
21
19
16
13
10
7
20
t.
4. 6
4. 8
5.0
5. 2
5. 4
5. 6
5. 8
6.0
6^.2
6. 4
t.
83
TABLE II. Relative humidity, per cent.
X5
Difference between the dry and wet thermometers (t t').
1
I
0.5
10.0
10.5
2.0
2. 5
3.0
3. 5
4.0
4. 5
5.0
5. 5
6.0
1
20
92
85
77
70
63
56
48
41
34
27
20
13
20
21
93
85
78
71
64
57
50
43
36
29
23
16
21
22
93
86
79
72
65
58
51
45
38
32
25
19
22
23
93
86
80
73
66
60
53
46
40
34
27
21
23
24
93
87
80
74
67
61
54
48
42
36
30
24
24
25
94
87
81
74
68
62
56
50
44
38
32
26
25
26
94
88
81
75
69
63
57
51
45
40
34
28
26
27
94
88
82
76
70
64
59
53
47
42
36
30
27
28
94
88
82
77
71
65
GO
54
49
43
38
33
28
29
94
89
83
77
72
66
61
56
50
45
40
35
29
30
94
89
84
78
73
67
62
57
52
47
41
36
30
31
95
89
84
79
74
68
63
58
53
48
43
38
31
32
95
90
84
79
74
69
64
59
54
50
45
40
32
33
95
90
85
80
75
70
65
60
56
51
47
42
33
34
95
91
86
81
75
72
67
62
57
53
48
44
34
35
95
91
86
82
76
73
69
65
59
54
50
45
35
36
96
91
86
82
77
73
70
66
61
56
51
47
36
37
96
91
87
82
78
74
70
66
62
57
52
48
37
38
96
92
87
83
79
75
71
67
63
58
54
50
38
39
96
9'^
88
83
79
75
72
68
63
59
55
52
39
40
96
92
88
84
80
76
72
68
64
60
56
53
40
41
96
92
88
84
80
76
72
69
65
61
57
54
41
42
96
92
88
84
81
77
73
69
65
62
58
55
42
43
96
92
88
85
81
77
74
70
66
63
59
56
43
44
96
92
88
85
81
78
74
70
67
63
60
57
44
45
96
92
89
85
82
78
75
71
67
64
61
58
45
46
96
93
89
85
82
79
75
72
68
65
61
58
46
47
96
93
89
86
83
79
76
72
69
66
62
59
47
48
96
93
89
86
83
79
76
73
69
66
63
60
48
49
97
93
90
86
83
80
76
73
70
67
63
60
49
50
97
93
90
87
83
80
77
74
70
67
64
61
50
51
97
93
90
87
84
81
77
74
71
68
65
62
51
52
97
94
90
87
84
81
78
75
72
69
66
63
52
53
97
94
91
87
84
81
78
75
72
69
66
65
53
54
97
94
91
88
85
82
79
76
73
70
67
64
54
55
97
94
91
88
85
82
79
76
73
70
68
65
55
56
97
94
91
88
85
82
80
77
74
71
68
65
56
57
97
94
91
88
86
83
80
77
74
71
69
66
57
58
97
94
91
89
86
83
80
78
75
72
69
67
58
59
97
94
92
89
86
83
81
78
75
72
70
67
59
60
97
94
92
89
86
84
81
78
75
73
70
68
60
61
97
94
92
89
87
84
81
78
76
73
71
68
61
62
97
95
92
89
87
84
81
79
76
74
71
69
62
63
97
95
92
89
87
84
82
79
77
74
72
69
63
64
97
95
9-2
90
87
85
82
79
77
74
72
70
64
65
97
95
92
90
87
85
82
80
77
75
72
70
65
66
97
95
92
90
87
85
82
80
78
75
73
71
66
67
98
95
93
90
88
85
83
80
78
76
73
71
67
68
98
95
93
90
88
85
83
81
78
76
74
71
68
69
98
95
93
90
88
86
83
81
78
76
74
72
69
70
98
95
93
90
88
86
83
81
79
77
74
72
70
71
98
95
93
91
88
86
84
81
79
77
75
72
71
72
98
95
93
91
88
86
84
82
79
77
75
73
72
73
98
95
93
91
88
86
84
82
80
78
75
73
73
74
98
95
93
91
88
86
84
82
80
78
76
74
74
75
98
95
93
91
89
87
84
82
80
78
76
74
75
76
98
95
93
91
89
87
85
82
80
78
76
74
76
77
98
95
93
91
89
87
85
83
80
78
76
74
77
78
98
96
93
91
89
87
85
83
81
79
77
75
78
79
98
96
94
91
89
87
85
83
81
79
77
75
79
80
98
96
94
92
89
87
85
83
81
79
77
75
80
t.
0.5
iM
*.
2.0
2. 5
3.0
3. 5
4.0
4. 5
6.0
5. 5
6.0
.t
9377
84
TABLE II. Relative humidity, per cent.
t
(Dryther.)
Difference between the dry and wet thermometers (t t').
t
(Dry ther.)
\
6.0
6. 5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10. 5
11.0
11.5
12.0
19
10
19
20
13
6
20
21
16
9
2
21
22
19
12
6
22
23
21
15
9
2
23
24
24
17
11
6
24
25
26
20
14
8
3
25
26
28
23
17
11
6
26
27
30
25
19
14
9
3
27
28
33
27
22
17
11
6
1
28
29
35
29
24
19
14
9
4
29
30
36
31
26
22
17
12
7
2
30
31
38
33
29
24
19
14
10
5
31
32
40
35
31
26
21
17
12
8
3 '
32
33
42
37
33
28
24
19
15
10
6
2
33
34
44
39
35
30
26
21
17
13
9
4
34
35
45
41
37
32
28
24
19
15
12
7
3
35
36
47
43
38
34
30
26
22
18
14
10
6
2
36
37
48
44
40
36
32'
28
24
20
16
12
8
5
1
37
38
50
46
42
38
34
30
26
22
18
15
11
7
3
38
39
52
48
44
40
36
32
28
24
20
17
13
9
6
39
40
53
49
45
41
38
34
30
26
22
19
16
12
8
40
41
54
50
46
43
39
36
32
29
24
21
18
14
10
41
42
55
51
48
44
40
37
34
30
27
23
20
16
13
42
43
56
52
49
46
42
38
35
32
29
25
22
19
15
43
44
57
53
50
47
43
40
37
33
30
27
24
21
17
44
45
58
54
51
48
44
41
38
35
32
29
25
22
19
45
46
58
55
52
49
46
42
39
36
33
30
27
23
21
46
47
59
56
63
50
47
44
40
38
34
31
28
25
22
47
48
60
56
53
51
48
45
42
39
36
33
30
27
24
48
49
60
57
54
52
49
46
43
40
37
34
31
29
26
49
50
61
58
55
52
50
47
44
41
38
36
33
30
27
50
51
62
69
56
53
50
48
45
42
39
37
34
31
28
51
52
63
60
57
54
51
48
46
43
40
38
35
33
30
52
53
63
61
58
55
52
49
47
44
42
39
36
34
31
53
54
64
61
59
56
53
50
48
45
43
40
38
35
32
54
55
65
62
59
57
54
51
49
46
43
41
39
36
34
55
56
65
63
60
57
55
52
50
47
44
42
40
37
35
56
57
66
64
61
58
55
53
50
48
45
43
40
38
36
57
58
67
64
61
59
56
53
51
49
46
44
42
39
37
58
69
67
65
62
60
57
54
52
49
47
45
43
40
38
59
60
68
65
63
60
58
55
53
50
48
46
44
41
39
60
61
68
66
63
61
58
56
54
51
49
47
44
42
40
61
62
69
66
64
61
59
57
54
52
50
47
45
43
41
62
63
69
67
64
62
60
57
55
53
51
48
46
44
42
63
64
70
67
65
62
60
58
56
53
51
49
47
45
43
64
65
70
68
65
63
61
59
56
54
52
50
48
46
44
65
66
71
68
66
63
61
59
57
55
53
51
49
47
45
66
67
71
69
66
64
62
60
58
55
53
51
49
47
45
67
68
71
69
67
65
63
60
58
56
54
52
50
48
46
68
69
72
70
67
65
63
61
59
57
55
53
51
49
47
69
70
72
70
68
66
64
62
60
57
55
53
52
50
48
70
71
72
70
68
66
64
62
60
58
56
54
52
50
48
71
72
73
71
69
67
65
63
61
59
57
55
53
51
49
72
73
73
71
69
67
65
63
61
59
57
55
53
52
50
73
74
74
72
70
68
66
64
62
60
58
56
54
52
50
74
75
74
72
70
68
66
64
62
60
58
56
55
53
51
75
76
74
72
70
68
66
64
63
61
sa
57
55
53
52
76
77
74
73.
71
69
67
65
63
61
59
57
56
54
52
77
78
75
73
71
69
67
65
63
62
60
58
56
54
53
78
79
75
73
71
70
68
66
64
62
60
58
57
55
53
79
80
75
73
72
70
68
66
64
63
61
59
57
55
54
80
f.
6.0
6.5
7 e .O
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
t.
85
TABLE II. Relative humidity, per cent.
I
Difference between the dry and wet thermometers (< O.
|j
JS
(^
12.
12. 5
13.
13. 5
14.
14. 5
15.
15. 5
16.
16. 5
17.
17. 5
18.
>>
.
40
8
5
1
40
41
10
7
4
41
42
13
10
6
3
42
43
15
12
9
5
2
43
44
17
14
11
8
5
1
44
45
19
16
13
10
7
4
1
45
46
21
18
15
12
9
6
3
46
47
22
20
16
14
11
8
5
3
47
48
24
21
19
16
13
10
7
5
2
48
49
26
23
20
17
15
12
9
7
4
1
49
50
27
24
22
19
16
14
11
9
6
4
1
50
61
28
26
23
21
18
16
13
10
8
5
3
51
52
30
27
24
22
20
17
15
12
10
7
5
2
52
63
31
29
26
24
21
19
16
14
12
9
7
4
2
53
54
32
30
28
25
23
20
18
15
13
11
8
6
4
54
55
34
31
29
26
24
22
19
17
15
12
10
8
6
55
56
35
33
30
28
25
23
21
19
16
14
12
10
8
56
57
36
34
32
29
27
24
22
20
18
16
13
11
9
57
58
37
35
33
30
28
26
24
21
19
17
15
13
11
58
59
38
36
34
31
29
27
25
23
21
18
16
14
12
59
60
39
37
34
32
30
28
26
24
22
20
18
16
14
60
61
40
38
35
33
32
29
27
25
23
21
19
17
15
61
62
41
39
37
34
32
30
28
26
24
22
20
18
16
62
63
42
40
38
36
33
31
29
28
26
24
22
20
18
63
64
43
41
38
36
34
32
30
29
27
25
23
21
19
64
65
44
42
39
37
35
33
31
29
28
26
24
22
20
65
66
45
42
40
38
36
34
32
30
29
27
25
23
22
66
67
45
43
41
39
37
35
33
32
30
28
26
25
23
67
68
46
44
42
40
38
36
34
33
31
29
27
26
24
68
69
47
45
43
41
39
37
35
33
32
30
28
26
25
69
70
48
46
44
42
40
38
36
34
33
31
29
27
26
70
71
48
46
45
43
41
39
37
.35
34
32
30
28
27
71
72
49
47
45
43
42
40
38
36
35
33
31
30
28
72
73
50
48
46
44
42
41
39
37
35
34
32
30
29
73
74
50
48
47
45
43
41
40
38
36
35
33
31
30
74
75
51
49
47
46
44
42
40
39
37
35
34
32
31
75
76
52
50
48
46
45
43
41
39
38
36
35
33
31
76
77
52
50
49
47
45
44
42
40
39
37
35
34
32
77
78
53
51
49
48
46
44
43
41
39
38
36
35
33
78
79
53
52
50
48
47
45
43
42
40
39
37
36
34
79
80
54
52
51
49
47
45
44
42
41
39
38
36
35
80
fc
12.
12. 5
13.
13. 5
14.
14. 5
15.
15. 5
16.
16. 5
17.
17. 5
18.
t.
TABLE II. Relative humidity, per cent.
?
Difference between the dry and wet thermometers (1 <').
y
2
1
18.0
19.0
20.0
21.0
22.
23.0
24.0
25.0
26.0
27.0
28.0
29.(>
30.0
*j&
,
55
6
1
55
50
8
3
56
57
9
5
57
58
11
7
2
58
59
12
8
4
59
60
14
10
6
2
60
61
15
11
7
3
61
62
16
13
9
5
1
62
63
18
14
10
7
3
63
64
19
15
12
8
5
1
64
65
20
17
13
10
6
3
65
66
22
18
14
11
8
4
1
66
67
23
19
16
12
9
6
2
67
68
24
20
17
14
10
7
4
1
68
69
25
22
18
15
12
8
5
2
69
70
26
23
19
16
13
10
7
4
1
70
71
27
24
20
17
14
11
8
5
2
71
72
28
24
22
18
15
12
9
6
3
1
72
73
29
25
22
19
16
13
10
8
5
2
73
74
30
26
23
20
18
15
12
9
6
3
1
74
75
31
27
24
21
19
16
13
10
7
5
2
75
76
31
28
25
22
20
17
14
11
8
6
3
1
76
77
32
29
26
23
20
18
15
12
10
7
4
2
77
78
33
30
27
24
21
19
16
13
11
8
6
3
1
78
79
34
31
28
25
22
19
17
14
12
9
7
4
2
79
80
35
32
29
26
23
20
18
15
13
10
8
6
3
80
t.
18.0
19.0
20.0
21.0
22.
23.
24.
25.
26.
27.0
28.0
29.0
303.0
t.
87
TABLE II. Relative humidity, per cent.
0)
Difference between the dry and wet thermometers (t t').
1
ft
10.0
2 J .0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
mo
12.0
"1
80
96
92
87
83
79
75
72
68
64
61
57
54
80
81
96
92
88
84
80
76
72
68
65
61
58
54
81
82
96
92
88
84
80
76
72
69
65
62
58
55
82
83
96
92
88
84
80
76
73
69
66
62
59
55
83
84
96
92
88
84
80
77
73
69
66
63
59
56
84
85
96
92
88
84
80
77
73
70
66
63
60
56
85
86
96
92
88
84
81
77
73
70
67
63
60
57
86
87
96
92
88
84
81
77
74
70
67
64
60
57
87
88
96
92
88
85
81
77
74
71
67
64
61
58
88
89
96
92
88
85
81
78
74
71
68
64
61
58
89
90
96
92
88
85
81
78
75
71
68
65
62
59
90
91
96
92
89
85
82
78
75
71
68
65
62
59
91
92
96
92
89
85
82
78
75
72
69
65
62
59
92
93
96
93
89
85
82
78
75
72
69
66
63
60
93
94
96
93
89
86
82
79
75
72
69
66
63
60
94
95
96
93
89
86
82
79
76
72
69
66
63
60
95
96
96
93
89
86
82
79
76
73
70
67
64
61
96
97
96
93
89
86
82
79
76
73
70
67
64
61
97
98
96
93
89
86
83
79
76
73
70
67
64
61
98
99
96
93
89
86
83
80
76
73
70
68
65
62
99
100
97
93
90
86
83
80
77
74
71
68
65
62
100
101
97
93
90
86
83
80
77
74
71
68
65
62
101
102
97
93
90
86
83
80
77
74
71
68
65
63
102
103
97
93
90
87
83
80
77
74
71
69
66
63
103
104
97
93
90
87
83
80
77
74
72
69
66
63
104
105
97
93
90
87
84
81
78
75
72
69
66
64
105
106
97
93
90
87
84
81
78
75
72
69
66
64
106
107
97
93
90
87
84
81
78
75
72
69
67
64
107
108
97
93
90
87
84
81
78
75
72
70
67
64
108
109
97
93
90
87
84
81
78
75
73
70
67
65
109
110
97
94
90
87
84
81
78
76
73
70
67
65
110
111
97
94
90
87
84
81
78
76
73
70
68
65
111
112
97
94
90
87
84
82
79
76
73
71
68
65
112
113
97
94
90
87
85
82
79
76
73
71
68
66
113
114
97
94
91
88
85
82
79
76
74
71
68
66
114
115
97
94
91
88
85
82
79
76
74
71
69
66
115
116
97
94
91
88
85
82
79
76
74
71
69
66
116
117
97
94
91
88
85
82
79
77
74
71
69
66
117
118
97
94
91
88
85
82
79
77
74
72
69
67
118
119
97
94
91
88
85
82
80
77
74
72
69
67
119
120
97
94
91
88
85
83
80
77
75
72
70
67
120
121
97
94
91
88
85
83
80
77
75
72
70
67
121
122
97
94
91
88
85
83
80
77
75
72
70
67
122
123
97
94
91
88
85
83
80
78
75
73
70
68
123
124
97
94
91
88
85
83
80
78
75
73
70
68
124
125
97
94
91
88
86
83
80
78
75
73
70
68
125
126
97
94
91
88
86
83
80
78
75
73
71
68
126
127
97
94
91
89
86
83
81
78
76
73
71
68
127
128
97
94
91
89
86
83
81
78
76
73
71
68
128
1*9
97
94
91
89
86
83
81
78
76
73
71
69
129
130
97
94
91
89
86
83
81
78
76
74
71
69
130
131
97
94
92
89
86
84
81
79
76
74
71
69
131
132
97
94
92
89
86
84
81
79
76
74
72
69
132
133
97
94
92
89
86
84
81
79
76
' 74
72
69
133
134
97
94
92
89
86
84
81
79
76
74
72
70
134
135
97
94
92
89
86
84
81
79
77
74
72
70
135
136
97
94
92
89
87
84
82
79
77
74
72
70
136
137
97
94
92
89
87
84
82
79
77
74
72
70
137
138
97
95
92
89
87
84
82
79
77
74
73
70
138
139
97
95
92
89
87
84
82
79
77
75
73
70
139
140
97
95
92
89
87
84
82
79
77
75
73
71
140
t.
1...
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
mo
12.0
t.
88
TABLE II. Eelative humidity, per cent.
?
Difference between the dry and wet thermometers ( t tf).
?
J9
- +-
~I
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.
21.0
22.0
23.0
24.0
|
80
54
51
47
44
41
38
35
32
29
26
23
20
18
80
81
54
51
48
44
41
38
35
33
30
27
24
21
19
81
82
55
52
48
45
42
39
36
33
31
28
25
22
20
82
83
55
52
49
46
43
40
37
34
31
29
26
23
21
83
84
56
53
49
4G
44
41
38
35
32
29
27
24
22
84
85
56
53
50
47
44
41
38
36
33
30
28
25
22
85
86
57
54
51-
48
45
42
39
36
34
31
29
26
23
86
87
57
54
51
48
45
42
40
37
34
32
30
27
24
87
88
58
55
52
49
46
43
40
38
35
32
30
27
25
88
89
58
55
52
49
46
44
41
38
36
33
31
28
26
89
90
59
56
53
50
47
44
41
39
36
34
32
29
26
90
91
59
56
53
50
47
45
42
39
37
35
33
30
27
91
92
59
56
54
51
48
45
43
40
37
35
33
30
28
92
93
60
57
54
51
48
46
43
41
38
36
34
31
29
93
94
60
57
54
52
49
46
44
41
39
36
34
31
29
94
95
60
58
55
52
49
47
44
42
39
37
35
32
30
95
96
61
58
55
53
50
47
45
42
40
37
36
33
30
96
97
61
58
56
53
50
48
45
43
40
38
36
33
31
97
98
61
59
56
53
51
48
46
43
41
38
37
34
32
*98
99
62
59
56
54
51
49
46
44
41
39
37
34
32
99
100
62
59
57
54
51
49
47
44
42
39
37
35
33
100
101
62
60
57
54
52
49
47
45
42
40
38
36
33
101
102
63
60
57
55
52
50
47
45
43
40
38
36
34
102
103
63
60
58
55
53
50
48
45
43
41
39
37
34
103
104
63
61
58
55
53
51
48
46
44
41
39
37
35
104
105
64
61
58
56
53
51
49
46
44
42
40
38
35
105
106
64
61
59
56
54
51
49
47
44
42
40
38
36
106
107
64
62
59
57
54
52
49
47
45
43
41
38
36
107
108
64
62
59
57
64
52
50
47
45
43
41
39
37
108
109
65
62
60
57
55
52
50
48
46
44
41
39
37
109
110
65
62
60
57
55
53
50
48
46
44
42
40
38
110
111
65
63
60
58
55
53
51
49
46
44
42
40
38
111
112
65
63
60
58
56
53
51
49
47
45
43
40
39
112
113
66
63
61
58
56
54
51
49
47
45
43
41
39
113
114
66
63
61
59
56
54
52
50
48
45
44
41
39
114
115
66
64
61
59
57
54
52
50
48
46
44
42
40
115
116
66
64
61
59
57
55
52
50
48
46
44
42
40
116
117
66
64
62
59
57
55
53
51
49
46
44
43
41
117
118
67
.64
62
60
57
55
53
51
49
47
45
43
41
118
119
67
64
62
60
58
55
53
51
49
47
45
43
41
119
120
67
65
62
60
58
56
54
51
49
47
45
44
42
120
121
67
65
63
60
58
56
54
52
50
48
46
44
42
121
122
67
65
63
61
58
56
54
52
50
48
46
44
42
122
123
68
65
63
61
59
57
54
52
50
48
46
45
43
123
124
68
66
63
61
59
57
55
53
51
49
47
45
43
124
125
68
66
64
62
59
57
55
53
51
49
47
45
43
125
126
68
66
64
62
59
57
55
53
51
49
47
46
44
126
127
68
66
64
62
60
58
55
54
52
50
48
46
44
127
128
68
66
64
62
60
58
56
54
52
50
48
46
44
128
129
69
66
64
62
60
58
56
54
52
50
48
46
45
129
130
69
67
65
62
60
58
56
54
52
50
49
47
45
130
131
69
67
65
63
60
58
56
54
53
51
49.
47
45
131
132
69
67
65
63
61
59
57
55
53
51
49
47
46
132
133
69
67
65
63
61
59
57
55
53
51
49
48
46
133
134
70
67
65
63
61
59
57
55
53
51
50
48
46
134
135
70
68
65
63
61
59
57
55
53
51
50
48
46
135
136
70
68
66
64
61
59
58
56
54
52
50
48
47
136
137
70
68
66
64
62
60
58
56
54
52
50
49
47
137
138
70
68
66
64
62
60
58
56
54
52
51
49
47
138
139
70
68
66
64
62
60
58
56
54
53
51
49
47
139
140
71
68
66
64
62
60
58
56
55
53
51
49
48
140
t.
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
21.0
22.0
23.0
24.0
t.
89
TABLE II. Relative humidity, per cent.
.1
Difference between the dry and wet thermometers (t if).
I
4.0
25.0
26.0
27.0
8.0
29.0
30.0
31.0
32.0
33.0
34.0
35.0
36.0
~|
80
18
15
13
10
8
6
3
1
80
81
19
16
14
11
9
7
4
2
81
82
20
17
15
12
10
8
5
3
1
82
83
21
18
16
13
11
9
6
4
2
83
84
22
19
17
14
12
10
8
5
3
1
84
85
22
20
17
15
13
11
9
6
4
2
85
86
23
21
18
16
14
12
10
7
5
3
1
86
87
24
22
19
17
15
13
11
8
6
4
2
87
88
25
22
20
18
16
14
12
9
7
5
3
1
88
89
26
23
21
19
16
14
12
10
8
6
4
2
1
89
90
26
24
22
20
17
15
13
11
9
7
5
3
2
90
91
27
25
23
20
18
16
14
12
10
8-
6
4
3
91
92
28
26
23
21
19
17
15
13
11
9
7
5
3
92
93
29
26
24
22
20
18
16
14
12
10
8
6
4
93
94
29
27
25
23
21
18
16
14
13
11
9
7
5
94
95
30
28
25
23
21
19
17
15
13
11
10
8
6
95
96
30
28
26
24
22
20
18
16
14
12
10
9
7
96
97
31
29
27
25
23
21
19
17
15
13
11
10
8
97
98
32
29
27
25
23
21
19
18
16
14
12
10
9
98
99
32
30
28
26
24
22
20
18
16
15
13
11
10
99
100
33
31
29
27
25
23
21
19
17
15
14
12
10
100
101
33
31
29
27
25
23
21
20
18
16
14
13
11
101
102
34
32
30
28
26
24
22
20
19
17
15
13
12
102
103
34
32
30
28
26
25
23
21
19
17
16
14
12
103
104
35
33
31
29
27
25
23
22
20
18
16
15
13
104
105
35
33
31
30
28
26
24
22
20
19
17
15
14
105
106
36
34
32
30
28
26
25
23
21
19
18
16
14
106
107
36
34
32
31
29
27
25
23
22
20
18
17
15
107
108
37
35
33
31
29
27
26
24
22
21
19
17
16
108
109
37
35
33
32
30
28
26
25
23
21
20
18
16
109
110
38
36
34
32
30
28
27
25
23
22
20
19
17
110
111
38
36
34
33
31
29
27
26
24
22
21
19
18
111
112
39
37
35
33
31
29
28
26
24
23
21
20
18
112
113
39
37
35
33
32
30
28
27
25
23
22
20
19
113
114
39
38
36
34
32
30
29
27
25
24
22
21
19
114
115
40
38
36
34
33
31
29
28
26
24
23
21
20
115
116
40
39
37
35
33
31
30
28
26
25
23
22
20
116
117
41
39
37
35
33
32
30
29
27
25
24
22
21
117
118
41
39
37
36
34
32
31
29
27
26 24
23 .
21
118
119
41
40
38
36
34
33
31
29
28
26
25
23
22
119
120
42
40
38
36
35
33
31
30
28
27
25
24
22
120
121
42
40
38
37
35
33
32
30
29
27
26
24
23
121
122
42
41
39
37
35
34
32
31
29
28
26
25
23
122
123
43
41
39
37
36
34
33
31
29
28
26
25
24
123
124
43
41
40
38
36
35
33
31
30
28
27
25
24
124
125
43
42
40
38
37
35
33
32
30
29
27
26
24
125
126
44
42-
40
39
37
35
34
32
31
29
28
. 26
25
126
127
44
42
41
39
37
36
34
32
31
30
28
27
25
127
128
44
43
41
39
38
36
34
33
31
30
29
27
26
128
129
45
43
41
40
38
36
35
33
32
30
29
28
26
129
130
45
43
42
40
38
37
35
33
32
31
29
28
27
130
131
45
44
42
40
39
37
35
34
32
31
30
28
27
131
132
46
44
42
40
39
37
36
34
33
31
30
29
27
132
13'
46
44
42
41
39
38
36
35
33
32
30
29
28
133
134
46
44
43
41
39
38
36
35
33
32
31
29
28
134
135
46
45
43
41
40
38
37
35
34
32
31
30
28
135
136
47
45
43
42
40
39
37
36
34
33
31
30
29
136
13'
47
45
44
42
40
39
37
36
34
33
32
30
29
137
138
139
47
47
45
46
44
44
42
42
41
41
39
39
38
38
36
37
35
35
33
34
32
32
31
31
29
30
138
139
140
48
46
44
43
41
40
38
37
35
34
33
31
30
140
t.
24.0
25.0
26.0
27 c .O
28.0
29.
30.
31.
32.0
33.0
34.
35.0
36.
t.
90
TABLE II. Relative humidity, per cent.
J
Difference between the dry and wet thermometers (t f).
J
b
e^
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
b
0,
89
1
89
90
2
90
91
3
1
91
92
3
2
1
92
93
4
3
2
93
94
5
4
8
94
95
6
5
4
1
95
96
7
5
5
2
1
96
97
8
6
6
3
1
97
98
9
7
7
4
2
1
98
99
10
8
7
5
3
2
99
100
10
9 '
8
6
4
3
1
100
301
11
9
9
6
5
3
2
101
102
12
10
9
7
6
4
3
1
102
103
12
11
9
8
6
5
4
2
1
103
104
13
12
10
8
7
6
5
3
2
104
105
14
12
11
9
8
6
6
4
2
1
105
106
14
13
11
10
8
7
6
4
3
2
106
107
15
14
12
11
9
8
6
5
4
3
1
107
108
16
14
13
11
10
9
7
6
5
3
2
1
108
109
16
15
13
12
10
9
8
7
5
4
3
1
109
110
17
15
14
13
11
10
8
7
6
5
3
2
1
110
111
18
16
15
13
12
10
9
8
7
5
4
3
2
111
112
18
17
15
14
12
11
10
8
7
6
5
4
2
112
113
19
17
16
14
13
12
10
9
8
7
5
4
3
113
114
19
18
16
15
14
12
11
10
8
7
6
5
4
114
115
20
18
17
16
14
13
12
10
9
8
7
6
4
115
116
20
19
17
16
15
13
12
11
10
8
7
6
5
116
117
21
19
18
17
15
14
13
11
10
9
8
7
6
117
118
21
20
18
17
16
15
13
12
11
10
8
7
6
118
119
22
20
19
18
16
15
14
12
11
10
9
8
7
119
120
22
21
19
18
17
16
14
13
12
11
10
9
8
120
121
23
21
20
18
17
16
15
13
12
11
10
9
8
121
122
23
22
20
19
18
17
15
14
13
12
11
10
9
122
123
24
22
21
19
18
17
16
14
13
12
11
10
9
123
124
24
23
21
20
19
18
16
15
14
13
12
11
9
124
125
24
23
22
20
19
18
17
15
14
13
12
11
10
125
126
25
23
22
21
20
19
17
16
15
14
13
12
10
126
127
25
24
23
21
20
19
18
16
15
14
13
12
11
127
128
26
24
23
22
21
19
18
17
16
15
14
13
11
128
129
26
25
24
22
21
20
19
17
16
15
14
13
12
129
130
27
25
24
23
21
20
19
18
17
16
15
14
12
130
131
27
26
24
23
22
21
19
18
17
16
15
14
13
131
132
27
26
25
23
22
21
20
19
18
16
15
14
13
132
133
28
26
25
24
23
21
20
19
18
17
16
15
14
133
134
28
27
25
24
23
22
21
19
18
17
16
15
14
134
135
28
27
26
24
23
22
21
20
19
18
17
16
15
135
136
29
27
26
25
24
22
21
20
19
.18
17
16
15
136
137
29
28
26
25
24
23
22
20
19
18
17
16
15
137
138
29
28
27
25
24
23
22
21
20
19
18
17
16
138
139
30
28
27
26
25
24
22
21
20
19
18
17
16
139
140
30
29
28
2G
25
24
23
22
21
20
18
17
16
140
t.
36.
37.
38.
39.
40 c .O
41.
42.
43.
44.
45.
46.
47.
48.
t.
91
TABLE III. Correction to vapor pressure for reading of barometer.
1
Inches.
p
7
30
29
28
27
26
25
24
23
22
21
20
19
18
T
.
.000
.000
+ .001
+ .001
+.001
+ .002
+.002
+ .003
+.003
+ .003
+ .004
+.004
+.004
i
2
.000
.000
.001
.002
.002
.003
.004
-.005
.006
.007
.007
.008
.009
2
3
.001
.000
.001
.002
.003
.004
.006
.007
.008
.009
.010
.011
.012
3
4
-.001
.000
.002
.003
.005
.006
.008
.009
.011
.012
.014
.015
.017
4
5
-.001
+ .001
.002
.004
.006
.008
.010
.012
.014
.015
.017
.019
.021
5
G
001
001
003
005
008
010
.012
.014
016
019
021
.023
025
6
7
-.001
.001
.003
.006
.009
.012
.014
.017
.019
.022
.024
.027
.030
7
8
-.001
.001
.004
.007
.010
.013
.016
.019
.022
.025
.028
.031
.034
8
9
-.001
.002
.005
.008
.012
.015
.018
.022
.025
.028
.032
.035
.038
9
10
-.002
.002
.005
.009
.013
.017
.020
.024
.027
.031
.035
.039
.043
10
11
-.002
.002
.000
.010
.014
.018
.022
.026
.031
.035
.039
.043
.047
11
12
-.003
.002
.006
.010
.015
.019
.024
.028
.032
.037
.041
.046
.050
12
13
-.003
' .002
.006
.011
.016
.021
.026
.030
.035
.040
.045
.050
.055
13
14
-.004
.002
.007
.012
.017
.022
.028
.033
.038
.043
.048
.054
.Oo9
14
15
-.004
.002
.007
.013
.019
.024
.030
.035
.041
.046
.052
.058
.063
15
16
004
002
.008
014
020
.026
.032
.038
.044
.049
.055
.061
067
16
17
-.004
.002
.008
.015
.021
.027
.034
.040
.046
.053
.059
.065
.072
17
18
-.004
.002
.009
.016
.022
.029
.036
.042
.049
.056
.062
.069
.076
18
19
-.005
.002
.009
.017
.024
.031
.038
.045
.052
.059
.066
.073
.080
19
20
.005
.003
.010
.018
.026
.033
.041
.048
.055
.063
.070
.078
.085
20
21
.005
.003
.011
.019
.027
.034
.042
.050
.057
.066
.073
.081
.089
21
22
.005
.003
.011
.020
.028
.036
.044
.052
.061
.069
.077
.085
.093
22
-23
.005
.003
.012
.021
.029
.038
.046
.055
.063
.072
.081
.089
.098
23
24
.005
.004
.013
.021
.030
.039
.048
.057
.066
.075
.084
.093
.102
24
25
.006
.004
.013
.022
.032
.041
.050
.060
.069
.078
.088
.097
.106
25
26
.006
.004
.013
.023
.033
.043
.052
.062
.072
.081
.091
.101
.111
26
27
.006
.004
.014
.024
.034
.044
.054
.065
.075
.085
.095
.105
.115
27
28
-.006
.004
.015
.025
.036
.046
.056
.067
.077
.088
.098
.109
.119
28
29
.007
.004
.015
.026
.037
.048
.059
.069
.080
.091
.102
.113
.124
29
30
.007
.004
.016
.027
.038
.049
.061
.072
.083
.094
.105
.117
.128
30
31
.007
.005
.016
.028
.039
.051
.063
.074
.086
.097
.109
.121
.132
31
32
.007
.005
.017
.029
.041
.053
.065
.077
.089
.101
.113
.125
.137
32
33
.007
.005
.017
.030
.042
.054
.067
.079
.092
.104
.116
.129
.141
33
34
.008
.005
.018
.031
.043
.056
.069
.082
.094
.107
.120
.133
.145
34
35
.008
.005
.018
.032
.045
.058
.071
.084
.097
.110
.123
.137
.150
35
36
.008
.005
.019
.032
.046
.059
.073
.086
.100
.114
.127
.141
.154
36
37
.008
.006
.019
.033
.047
.061
.075
.089
.103
.117
.131
.145
.158
37
38
v.009
.006
.020
.034
.049
.063
.077
.091
.106
.120
.134
.149
.163
38
39
.009
.006
.021
.035
.050
.065
.079
.094
.109
.123
.138
.153
.167
39
40
.009
+.006
+.021
+.036
+.051
+ .066
+.081
+ .096
+.111
+.126
+ .142
+.157
+ .172
40
Dew Point
Pressure
Correction.
92
TABLE IV. Vapor pressure, in inches.
E
g
i
i
g
e
g
I
D
1
1
a
o>
"a
I
a
o>
c
g
a
1
"S
E
d
E
I
h
a
p.
'I
1
!_
'I
a
S-i
a
5
a
5
:
a
s
o
0,
y.
1
k
a
a
o
a
a
cS
01
0>
cS
cj
o
ft
ps>
ft
^f
ft
>
ft
n
Q
|^r
ft
60
.0010
30
.0069
.038
30
.164
60
.517
90
1.408
120
3.425
59
.0011
29
.0074
1
.040
31
.172
61
.536
91
1.453
121
3. 522
58
.0012
28
.0078
2
.043
32
.180
62
.555
92
1. 499
122
3.621
57
.0013
27
.0084
3
.045
33
.187
63
.575
93
1.546
123
3. 723
56
.0013
26
.0089
4
.047
34
.195
64
.595
94
1. 595
124
3.827
55
.0015
25
.0094
5
.049
35
.203
65
.616
95
1. 645
125
3.933
54
.0016
24
.010
6
.052
36
.211
66
.638
96
1.696
126
4.042
53
.0017
23
.011
7
.054
37
.219
67
.660
97
1.749
127
4.154
52
.0018
22
.011
8
.057
38
.228
68
.684
98
1.803
128
4.268
51
.0019
21
.012
9
.060
39
. 237
69
.707
99
1.859
129
4.385
50
.0021
20
.013
*10
.063
40
.246
70
.732
100
1.916
130
4.504
49
.0022
19
.013
11
.067
41
.256
71
.757
101
1.975
131
4.627
48
.0024
18
.014
12
.070
42
.266
72
.783
102
2.035
132
4. 752
47
.0026
17
.015
13
.074
43
.277
73
.810
103
2.097
133
4.880
46
.0027
16
.016
14
.077
44
.287
74
.838
104
2. 160
134
5.011
45
.0029
15
.017
15
.081
45
.298
75
.866
105
2.225
135
5.145
44
.00:51
14
.018
16
.085
46
.310
76
.896
106
2. 292
136
5.282
43
.0033
13
.019
17
.089
47
.322
77
.926
107
2.360
137
5.422
42
.0035
12
.020
18
.093
48
.334
78
.957
108
2.431
138
5.565
41
.0037
11
.021
19
.098
49
.347
79
.989
109
2.503
139
5.712
40
.0039
10
.022
20
.103
50
.360
80
1.022
110
2.576
140
5.862
39
.0041
9
.023
21
.108
51
.373
81
1.056
111
2.652
38
.0044
8
.025
22
.113
52
.387
82
1.091
112
2.730
37
.0046
- 7
.026
23
.119
53
.402
83
1. 127
113
2. 810
36
.0048
6
.028
24
.125
54
.417
84
1.163
114
2.891
35
.0051
5
.029
25
.130
55
.432
85
1.202
115
2.975
34
.0054
4
.031
26
.137
56
.448
86
1.241
116
3.061
33
.0058
3
.033
27
.143
57
.465
87
1.281
117
3.148
32
.0061
2
.034
28
.150
58
.481
88
1.322
118
3. 239
31
.0065
1
.036
29
.157
59
.499
89
1.364
119
3.331
Vapor
Pros-
sure.
93
TABLE V. Grains of water-vapor contained in a cubic foot of air.
J
3
1
2
3
4
5
6
7
8
9
I
j
20
.219
10
.356
.340
.324
.309
.294
.281
.267
.254
.242
.231
.564
.540
.516
.493
.471
.450
.430
.411
.391
.374
+ o
.564
.590
.617
.645
.674
.705
.735
.767
.801
.837
10
.87C
.910
.950
.991
1.033
1.075
1.122
1.169
1.217
1.268
20
1.321
1.374
1.430
1.488
1.550
1.611
1.675
1.743
1.812
1.884
30
1. 958
2.034
2.113
2.194
2.279
2.366
2.457
2.550
2.646
2.746
40
2.8*9
2.955
3.064
3.177
3.294
3.414
3.539
3.667
3.800
3.936
50
4.076
4.222
4.372-
4.526
4.685
4.849
5.01&
5.191
5.371
5.555
60
5.744
5.941
6.142
6. 350
6.563
6.782
7.009
7.241
7.480
7.726
70
7.980
8.240
8.508
8.782
9.065
9. 356
9.655
9.961
10. 277
10.601
80
10. 933
11. 275
11.626
11.987
12. 356
12. 736
13. 127
13. 576
13. 937
14.358
90
14. 791
15. 234
15. 688
16. 155
16. 634
17. 124
17. 626
18. 142
18. 671
19. 212
100
19. 766
20. 335
20. 917
21.514
22. 125
22. 751
94
TABLE VI. Reduction of barometer reading to 32.
Tempera-
ture.
Inches.
24.0
24.5
25.0
25.5
26.0
26.5
27.0
27.5
28.0
+.073
.070
.068
.065
.063
.060
.058
.055
28.5
29.0
29.5
30.0
30.5
31.0
+.081
.078
.075
.072
.070
.067
.064
061
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
+ .063
.060
.058
.056
.054
.052
.049
.047
.045
.043
+.064
.062
.060
.057
.055
.052
.051
.048
.046
.044
+.065
.063
.061
.058
.056
.054
.052
.049
.047
.045
+.067
.064
.062
.060
.057
.055
.052
.050
.048
.046
+ .068
.065
.063
.061
.058
.056
.054
.051
+.069 +.070
. 067 . t68
.065 .065
. 062 . 063
.060 .061
.057' .058
. 055 . 056
. 052' . 053
+.072
.Oi.9
.066
.064
.062
.059
.057
.054
+.075
.072
.069
.066
.064
.062
.059
056
+.076
.073
.070
.068
.065
.062
.060
057
+.077
.074
,072
.069
.066
.063
.061
058
+.078
.076
.073
.070
.067
.065
.062
059
+.080
.077
.074
.071
.068
.065
.063
060
.049
.046
.050
.047
.051
.048
.052
.049
.053
.050
.054
.051
.054
052
.055
.053
.050
.047
.045
.042
.039
.056
.054
.051
.048
.045
.043
.040
.057
.054
.052
.049
.046
.043
040
.058
.055
.053
.050
.047
.044
041
.041
.039
.036
.034
.032
.042
.039
.037
.035
.033
.042
.040
.038
.036
.033
.043
.041
.038
.036
.034
.044
.042
.039
.037
035
.045
.042
.040
.038
.035
.046
.043
.041
.038
.036
.047
.044
.041
.039
.036
.047
.045
.042
.040
.037
.048
.046
.043
.040
.038
.049
.047
.044
.041
039
.030
.028
.025
.023
.021
.030
.028
.026
.024
.022
.031
.029
.026
.024
.022
.031
.029
.027
.025
.022
.032
.030
.027
.025
023
.033 .033
.030 .031
.028 .029
.026 .026
. 023 . 024
.034
.031
.029
.026
024
.035
.032
.030
.027
.025
.035
.033
.030
.027
025
.036
.033
. 031
.028
.025
.036
.034
.031
.029
026
.087
.035
.032
.029
027
.038
.035
.032
.030
027
.038
.036
.033
.030
.027
.019
.017
.014
.019
.017
.015
.020
.017
.015
.020
.018
.015
.020
.018
016
.021
.018
.016
.021
.019
.016
.021
.019
.017
.022
.019
.017
.022
.020
.017
.023
. 020
.017
.023
.020
018
.024
.021
.018
.024
.021
.018
.016
.013
.024
.022
.019
.016
.013
.012
.010
.013
.010
.013
.011
.013
.011
.013
Oil
.014
.011
.014
.011
.014
.012
.014
.012
.015
012
.015
012
.015
012
.015
.013
.008
.006
.004
+.001
001
.008
.006
.004
+.001
001
.008
.006
.004
+.001
001
.008
.006
.004
+.001
001
.009
.006
.004
+.001
001
.009
.006
.004
+.002
001
. OO!)
.006
.004
+ .002
.001
.009
.007
.004
+.002
.001
.009
.007
.004
+ .002
001
.009
.007
.004
+ .002
001
.010
.007
.004
+ .002
.001
.010
.007
.004
+.002
.001
.010
.007
.004
+ .002
.001
.010
.007
.005
+ .002
.001
.010
.007
.005
+ .002
.001
.003
003
.003
003
003
.003
.003
.003
003
.004
.004
.004
.004
.004
.004
.005
.007
.010
012
.005
.008
.010
012
.005
.008
.010
.012
.005
.008
.010
012
.006
.008
.010
013
.006
.008
.010
013
.006
.008
.011
013
.006
.008
.011
013
.006
.009
.011
.014
.006
.009
.011
014
.006
.009
.012
.014
.006
.009
.012
014
.006
.009
.012
.015
.007
.009
.012
015
.007
.009
.012
.015
.014
.016
.018
.020
.023
025
.014
.016
.019
.021
.023
025
.014
.017
.019
.021
.024
026
.015
.017
.019
.022
.024
026
.015
.017
.020
.022
.024
027
.015
.018
.020
.022
.025
- 027
.016
.018
.021
.023
.025
028
.016
.018
.021
.023
.026
028
.016
.019
.021
.024
.026
.029
.016
.019
.022
.024
.027
030
.017
.019
.022
.025
.027
030
.017
.020
.022
.025
.028
030
.017
.020
.023
.026
.028
.031
.018
.020
.023
.026
.029
031
.018
.021
.024
.026
.029
.032
.027
.029
.031
.033
.036
.038
.040
.042
.044
.046
.027
.030
.032
.034
.037
.038
.041
.043
.045
.047
.028
.030
.033
.035
.037
.039
.042
.044
.046
.048
.029
.031
.033
.035
.038
.040
.042
.045
.047
.049
.029
.032
.034
.036
.039
.041
.043
.046
.048
.060
.030
.032
.035
.037
.039
.042
.044
.047
.049
.051
.0:50
.033
.035
.038
.040
.043
.045
.047
.050
.052
.031
.033
.036
.038
.041
.043
.046
.048
.051
.053
.031
.034
.036
.039
.042
.044
.047
.0^9
.052
.054
.032
.034
.037
.040
.042
.045
.0^8
.050
.052
.055
.033
.035
.038
.040
.043
.0^6
.048
.051
.054
-.056
.033
.036
.038
.041
.044
.04C
.049
.052
.054
-.057
.034
.036
.039
.042
.045
.047
.050
.053
.055
.058
.034
.037
.040
.042
.045
.048
.051
.053
.056
-.059
.035
.038
.040
.043
.046
.049
.052
.054
.057
-.060
95
TABLE VI Reduction of barometer reading to 32 Continued.
a
Inche
5.
I 5
24.0
24.5
25.0
25.5
26.0
26,5
27.0
27.5
28.0
28.5
29.0
29.5
30.0
30.5
31.0
50
.046
.047
.048
.049
. 050
.051
.052
. 053
.054
-.055
.056
.057
.058
.059
.060
51
.049
.050
.051
.052
.053
.054
.055
.056
.057
.058
.059
.060
.061
.062
.063
52
.051
.052
.053
.054
.055
.056
.057
.058
.059
.060
.061
.062
.064
.065
.066
53
.053
.054
.055
.056
.057
.058
.060
.061
.062
.063
.064
.065
.066
.067
.068
54
.055
.056
.057
.058
.060
.061
.062
.063
.064
.065
.067
.068
.069
.070
.071
55
.057
.058
.060
.061
.062
.063
.064
.065
.066
.068
.06,9
.070
.071
.073
.074
56
.060
.061
.062
.063
.064
.065
.067
.0(38
.069
.070
.072
.073
.074
.075
.077
57
OfiV!
.063
.064
.065
.067
.068
.069
.070
072
073
075
076
077
078
080
58
.0(14
.065
.066
.068
.069
.070
.071
.073
.074
.076
.077
.078
.080
.081
.082
59
.056
.068
.069
.070
.072
.073
.074
.075
.077
.078
.080
.'081
.083
.084
.085
60
.068
.070
.071
.072
.074
.076
.077
.078
.079
.081
.082
.084
.085
.086
.088
61
.070
.072
.073
.074
.076
.077
.079
.080
.082
.083
.085
.086
.088
.089
.091
62
.073
.074
.076
.077
.079
.080
.082
.083
.085
.036
.088
.089
.091
.092
.094
63
.075
.076
.078
.079
.081
.082
.084
.085
.087
.088
.090
.091
.093
.095
.096
64
.077
.078
.080
.081
.083
.085
.086
.088
.090
.091
.093
.094
.096
.097
.099
65
.079
.080
.082
.084
.086
.087
.089
.090
.092
.093
.095
.097
.099
.100
.102
66
.081
,083
.085
.086
.088
.089
.091
.093
.095
.096
.098
.099
.101
.103
.105
67
.083
.085
.087
.088
.090
.092
.094
.095
.097
.099
.101
.102
.104
.106
.108
68
.085
.087
.089
.090
.093
.094
.096
.098
.100
.101
.103
.105
.107
.108
.110
69
.088
.089
.091
.093
.095
.097
.099
.100
.102
.104
.106
.107
.110
.111
.113
70
.090
.092
.094
.096
.097
.099
.101
.103
.105
.106
.109
.110
.112
.114
.116
71
.092
.094
.096
.098
.100
.101
.103
.105
.107
.109
.111
.113
.115
.116
.119
72
.094
.096
.098
.100
.102
.104
.106
.108
.110
.112
.114
.116
.118
.120
.122
73
.096
.098
.100
.102
.104
.106
.108
.110
.112
.114
.116
.118
.120
.122
.124
74
.098
.100
.103
.105
107
.109
.111
.113
.115
.117
.119
.121
.123
.126
.127
75
.101
.102
.105
.106
.109
.111
.113
.115
.117
.119
.122
.124
.126
.128
.130
76
.103
.104
.107
.109
.111
.113
.116
.118
.120
.122
.124
.126
.128
.130
.133
77
.105
.107
.109
.111
.114
.116
.118
.120
.122
.124
.127
.129
.131
.133
.136
78
.107
.109
.112
.113
.116
.118
.120
.122
.125
.127
.129
.131
.134
.136
.138
79
.109
.111
.114
.116
.118
.120
.123
.125
.127
.129
.132
.134
.137
.139
.141
80
111
113
116
118
121
123
.125
127
.130
.132
.135
.137
139
.141
.144
81
.114
.116
.118
.120
.123
.125
.128
.130
.132
.134
.137
.139
.142
.144
.147
82
.116
.118
.121
.122
.125
.128
.130
.132
.135
.137
.140
.142
.145
.147
.149
83
.118
.120
.123
.125
.128
.130
.133
.135
.138
.140
.142
.145
.147
.149
.152
84
.120
.122
.125
.127
.130
.132
.135
.138
.140
.142
.145
.147
.150
.152
.155
85
.122
.124
.127
.129
.132
.134
.137
.139
.143
.145
.148
.150
.153
.155
.158
86
.124
.126
.128
.130
.135
.137
.140
.143
.145
.148
.150
.153
.155
.158
.161
87
.126
.129
.132
.134
.137
.139
.142
.144
.148
.150
.153
.155
.158
.161
.163
88
.129
.131
.134
.137
.139
.142
.145
.147
.150
.152
.155
.158
.161
.163
.166
89
.131
.133
.136
.139
.142
.144
.147
.150
.153
.155
.158
.161
.164
.166
.169
90
.133
.136
.138
.141
.144
.147
.150
.153
.155
.157
.161
.164
.166
.169
.172
91
.135
.138
.141
.143
.146
.149
.152
.155
.158
.160
.163
.166
.169
.172
.175
92
.137
.140
.143
.146
.149
.152
.154
.157
.160
.163
.166
.169
.172
.175
.177
93
.139
.142
.145
.148
.151
.154
.157
.160
.163
.166
.168
.171
.174
.177
.180
94
.142
.145
.147
.150
.153
.156
.159
.162
.165
.168
.171
.174
.177
.180
.183
95
.141
.147
.150
.153
.156
.159
.162
.165
.168
.171
.174
.177
.180
.183
.186
96
.146
.149
.152
.155
.158
.161
.164
.167
.170
.173
.176
.179
.182
.185
.188
97
.148
.151
.154
.157
.160
.164
.167
.170
.173
.176
.179
.182
.185
.188
.191
98
.150
.153
.156
.160
.163
.166
.169
.172
.175
.178
.181
.185
.188
.191
.194
99
.152
.155
.159
.162
.165
.168
.171
.175
.178
.181
.184
.187
.190
.194
.197
100
.154
.157
.161
.164
.167
.171
-.174
-.177
.180
.184
-.187
.190
-.193
.197
.200
96
TABLE VII. Table for reducing observations of the barometer to sea-level, correction additive.
a
Temperature of external air degrees Fahrenheit.
El
.1
20
10
10
20
30
40
50
60
70
80
90
100
10
.013
.013
.012
.012
.012
.012
.011
.011
.011
.011
.010
.010
.010
20
.026
.025
.025
.024
.023
.023
023
022
.022
021
021
020
020
30
.039
.038
.037
.036
.035
.034
.034
.033
.032
.032
.031
.030
.030
40
.052
.050
.049
.048
.047
.046
.045
. .044
.043
.042
.041
.040
.040
50
.065
.063
.061
.060
.059
.058
.056
.055
.054
.053
.052
.051
.050
60
.077
.076
.074
.072
.070
.069
.068
.066
.065
.063
.062
.061
.059
70
.090
.088
.086
084
082
.081
078
.077
076
074
072
071
069
80
.103
.101
.098
.096
.094
.092
.090
.088
.086
.084
.082
.081
.079
yd
.116
.113
.111
.108
105
104
101
.099
097
095
093
091
089
100
.129
.126
.123
.120
117
115
112
.110
108
105
.103
101
099
110
.142
.139
.135
.132
.129
.126
.123
.121
.119
.116
.113
.111
.109
120
.155
.151
.148
.144
.140
.138
.134
.132
.129
.126
.124
.121
.119
130
.168
.164
.160
.156
.152
.149
.146
.143
.140
.137
.134
.131
.129
140
.181
.176
.172
.168
.164
.161
.157
.154
.151
.147
.144
.141
.139
150
.194
.189
.185
.180
.176
.172
.168
.165
.162
.158
. 155
.152
.149
160
.206
.201
.197
.192
.187
.183
.179.
.176
.172
.168
.165
. 162
.158
170
.219
.214
.209
.204
.199
.195
.190
.187
.183
.179
.175
.172
.168
180
.232
.227
.222
.216
.211
.206
.202
.198
.194
.189
.185
.182
.178
190
.245
.239
.234
.228
.222
.218
.213
.209
.204
.200
.196
.192
..188
200
.258
' .252
.246
.240
.234
.229
.224
.220
.215
.210
.206
.202
.198
210
.271
.264
.258
.252
246
240
.235
.231
226
.221
.216
.212
208
220
.284
.277
.270
.264
.257
.252
.246
.242
.236
.231
.227
.222
.218
230
.296
.289
.283
.276
269
263
.257
253
247
.242
.237
.232
228
240
.309
.302
.295
.288
.281
.275
.269
.264
.258
.252
.248
.242
.238
250
.322
.314
.307
.300
.293
.286
.280
.275
.269
.263
.258
.253
.248
260
.335
.327
.319
311
304
297
291
285
279
.273
.268
.263
257
270
.348
.339
.331
.323
.316
.309
.302
.296
.290
.284
.278
.273
.267
280
.3(50
.352
.344
.335
.328
.320
.314
.307
.301
.294
.288
.283
.277
290
.373
.364
.356
.347
.339
.332
.325
.318
.311
.305
.299
.293
.287
300
.386
.377
.368
.359
.351
.343
.336
.329
.322
.315
.309
.303
.297
310
.399
.389
.380
.371
.363
.354
.347
.340
.333
.326
.319
.313
.307
320
.412
.402
.392
.383
.374
.366
.358
.351
.343
.336
.329
.323
.317
330
.424
.414
.404
.395
.386
.377
.369
.362
. .354
.347
.340
.333
.326
340
.437
.427
.416
.407
.397
.389
.380
.373
.365
.357
.350
.343
.336
350
.450
.439
.429
.419
.409
.400
.392
.384
.376
.368
.360
.353
.346
360
.463
.451
.441
.430
.421
.411
.403
.394
.386
.378
.370
.363
.356
370
.476
.464
.453
.442
.432
.423
.414
.405
.397
.389
.380
.373
.366
380
.488
.476
.465
.454
.444
.434
.425
.416
.408
.399
.391
.383
.375
390
.501
.489
.477
.466
.455
.446
.436
.427
.418
.410
.401
.393
.385
400
.514
.501
.489
.478
.467
.457
.447
.438
.429
.420
.411
.403
.395
410
.527
.513
.501
.490
.479
.468
.458
.449
.440
.430
.421
.413
.405
420
.539
.526
.513
.502
.490
.480
.469
.460
.450
.441
.431
.423
.415
430
.552
.538
.525
.513
.502
.491
.480
.470
.461
.451
.442
.433
.425
440
.565
.551
.537
.525
.513
.502
.491
.481
.471
.462
.452
.443
.434
450
.578
.563
.550
.537
.525
.513
.503
.492
.482
.472
.462
.453
.444
460
.590
.575
.562
.549
.537
.525
.514
.503
.493
.482
.472
.463
.454
470
.603
.588
.574
.561
.548
.536
.525
.514
.503
.493
.482
.473
.464
480
.616
.600
.586
.572
.560
.547
.536
.524
.514
.503
.493
.483
.474
490
.628
.613
.598
.584
.571
.559
.547
.535
.524
.514
.503
.493
.483
500
.641
.625
.610
.596
.583
.570
.558
.646
.535
.524
.513
.503
.493
510
.654
.637
.622
.608
.594
.581
.569
.557
.545
.534
.523
.513
.503
520
.666
.650
.634
.620
.606
.593
.580
.568
.556
.545
.533
.523
.513
530
.679
.662
.646
.631
.617
.604
.591
.578
.566
.555
.544
.533
.522
540
.691
.675
.658
.643
.629
.615
.602
.589
.577
.565
.554
.543
.532
550
.704
.687
.670
.655
.640
.626
.613
.600
.587
.575
.564
.553
.542
560
.717
.699
.683
.667
.652
.638
.624
.611
.598
.586
.574
.563
.552
570
.729
.712
.695
.679
.663
.649
.635
.622
.608
.596
.584
.573
.562
580
.742
.724
.707
.690
.675
.660
.646
.632
.619
.606
.595
.583
.571
590
.754
.737
.719
.702
.686
.672
.657
.643
.629
.617
.605
.593
.581
600
.767
.749
.731
.714
.698
.683
.668
.654
.640
.627
.615
.603
.591
610
.780
.761
.743
.726
.709
.694
.679
.665
.650
.637
.625
.613
.601
620
.792
.774
.755
.738
.721
.705
.690
.675
.661
.648
.635
.623
.611
630
.805
.786
.767
.749
.732
.717
.701
.686
.671
.658
.645
.633
.620
640
.817
,798
,779
,761
,744
,728
,712
.697
.682
.668
.655
.643
.630
97
TABLE VII. For reducing observations, etc. Continued.
_g
Temperature of external air degrees Fahrenheit.
|1
H
20
10
10
20 30
40
50
60
70
800
90
100
i
650
.830
.811
.791
.773
.755
.739
.723
.708
.692
.679
.666
.653
.640
660
.843
.823
.803
.785
.767
.750
.734
.718
.703
.689
.676
.662
.650
670
.855
.835
.815
.797
.778
.761
.745
.729
.713
.699
.686
.672
.660
680
.868
.847
.827
.808
.790
.773
.756
.740
.724
.709
.696
.682
.669
690
.880
.860
.839
.820
.801
.784
.767
.750
.734
.720
.706
.692
.679
700
.893
.872
.851
.832
.813
.795
.778
.761
.745
.730
.716
.702
.689
710
.905
.884
.863
.844
.824
.806
.789
.772
.755
.740
.726
.712
.698
720
.918
.896
.875
.855
.836
.817
.800
.782
.766
.751
.736
.722
.708
730
.930
.909
.887
.867
.847
.829
.811
.793
.776
.761
.746
.732
.718
740
.943
.921
.899
.879
.859
.840
.822
.804
.787
.771
.756
.742
.728
750
.955
.933
.911
.891
.870
.851
.833
.815
.797
.782
.767
.752
.738
760
.968
.945
.922
.902
.881
.862
.843
.825
.808
.792
.777
.761
.747
770
.980
.957
.934
.914
.893
.873
.854
.836
.818
.802
.787
.771
.757
780
.993
.970
.946
.926
.904
.885
.865
.847
.829
.812
.797
.781
.767
790
1.005
.982
.958
.937
.916
.896
.876
.857
.839
.823
.807
.791
.776
800
1.018
.994
.970
.949
.927
.907
.887
.868
.850
.833
.817
.801
.786
810
1.030
1.00*6
.982
.961
.938^
.918
.898
.878
.860
.843
.827
.811
.796
820
1.043
1.018
.994
.972
.050
.929
.909
.889
.871
.854
.837
.821
.805
830
1 055
1.031
1. 006
.984
.961
.940
920
900
.881
864
847
831
.815
840
1.068
1.043
1.018
.995
.973
.951
.931
.911
.892
.874
.857
.841
850
1.080
1.055
1.030
1.007
.984
.962
.942
.922
.902
.885
.867
.851
.835
860
1.093
1.067
1.041
1.019
.995
.974
.952
.932
.913
.895
.877
860
.844
870
1.105
1.079
1.053
1.030
1.007
.985
.963
.943
.923
.905
.887
.870
.854
880
1.118
1.092
1.065
1.042
1.018
.996
.974
.954
.934
.915
.897
.880
.864
890
1.130
1.104
1.077
1.053
1.030
1.007
.985
.964
944
926
907
890
.873
900
1.143
1.116
1.089
1.065
1.041
1.018
.996
.975
.955
.936
.917
.900
.883
910
1.155
1.128
1.101
1.077
1.052
1.029
1.007
.986
.965
.946
.927
.910
.893
920
1.168
1.140
1.113
1.088
1.064
1.040
1.018
.996
.976
.956
.937
.920
.902
930
1.180
1.152
1. 125
1.100
1.075
1.051
1.029
1.007
.986
.967
.947
.929
.912
940
1.193
1.164
1.137
1.111
1.086
1.062
1.040
1.017
.997
.977
.957
.939
.921
950
1.205
1.177
1.149
1.123
1.098
1.074
1.051
1.028
1.007
.987
.967
.949
.931
960
1.217
1.189
1.160
1.135
1. 109
1.085
1.061
1.039
1.017
.997
.977
.959
.941
970
1.230
1.201
1.172
1.146
1.120
1.096
1.072
1.049
1.028
1.007
.987
.969
.950
980
1.242
1.213
1.184
1.158
1.131
1.107
1.083
1.060
1.038
1.018
.997
.978
.960
990
1.255
1.225
1.196
1.169
1.143
1.118
1.094
1.070
1.049
1.028
1,007
.988
.969
1,000
1.267
1.237
1.208
1.181
1.154
1.129
1.105
1.081
1.059
1.038
1.017
.998
.979
1,010
1.279
1.249
1.220
1.192
1. 165
1.140
1.116
1.092
1.069
1.048
1.027
1.008
.989
1,020
1.292
1.261
1.232
1.204
1.177
1.151
1.127
1.102
1.080
1.058
1.037
1.018
.998
1,030
1.304
1.273
1.243
1.215
1.188
1.162
1.137
1.113
1.090
1.069
1.047
1.027
1.008
1,040
1.317
1.285
1.255
1. 227
1.199
1.173
1.148
1.123
1.101
1.079
1.057
1.037
1.017
1,050
1.329
1.298
1.267
1.238
1.211
1.184
1.159
1.134
1.111
1.089
1.067
1.047
1.027
1,060
1.341
1.310
1.279
1.250
1.222
1.195
1.170
1.145
1.121
1.099
1.077
1.057
1.037
1,070
1.354
1/322
1.291
1.261
1.233
1.206
1.181
1.155
1. 132
1.109
1.087
1.067
1.046
1,080
1.366
1.334
1 302
1 273
1 244
1 217
1 191
1 166
1 142
1.120
1 097
1 076
1 056
1J090
1.379
1.346
1.314
1.284
1.256
1.228
1.202
1.176
1.153
1.130
1.107
1.086
1.065
1,100
1.391
1.358
1.326
1. 296
1.267
1.239
1.213
1.187
1.163
1.140
1.117
1.096
1.075
1,110
1.403
1.370
1.338
1.307
1.278
1.250
1.224
1.198
1.173
1.150
1.127
1.106
1.085
1,120
1.416
1.382
1.350
1.319
1.289
1.261
1.235
1.208
1.184
1.160
1.137
1.115
1.094
1,130
1.428
1. 394
1.361
1.330
1.301
1.272
1.245
1.219
1.194
1.170
1.147
1.125
1.104
1,140
1.440
1.406
1.373
1. 342
1.312
1.283
1.256
1.229
1.204
1.180
1.157
1.135
1.113
1,150
1.453
1.418
1.385
1.353
1.323
1.294
1.267
1.240
1.215
1.191
1.167
1.145
1.123
1,160
1.465
1.430
1.397
1.365
1.334
1.305
1.278
1.251
1.225
1.201
1.177
1.154
1.133
1,170
1.477
1.442
1.409
1.376
1.345
1.315
1.289
1.261
1.235
1.211
1.187
1.164
1.142
1,180
1.489
1.454
1.420
1.388
1.357
1. 327
1.299
1.272
1.245
1.221
1.197
1.174
1.152
1,190
1.502
1.466
1.432
1.399
1.368
1.338
1.310
1.282
1.256
1.231
1.207
1.183
1.161
1 200
1.514
1.478
1.444
1.411
1.379
1.349
1.321
1.293
1.266
1.241
1.217
1.193
1.171
1,210
1.526
1.490
1.456
1.422
1.390
1.360
1.332
1.303
1.276
1.251
1.227
1.203
1.180
1,220
1. 539
1. 502
1.467
1.434
1.401
1.371
1.342
1.314
1.288
1.261
1.237
1.212
1.190
1,230
1.551
1.514
1.479
1.445
1.413
1.382
1.353
1.324
1.297
1.271
1.247
1.222
1.199
1,240
1.563
1.526
1.491
1.457
1.424
1.393
1.364
1.335
1.307
1.281
1.257
1.232
1.209
1,250
1. 576
1. 538
1.502
1.468
1.435
1.404
1.374
1.345
1.317
1.291
1.266
1.242
1.218
1,260
1.588
1.550
1.514
1.479
1.446
1.415
1.385
1.356
1.328
1.302
1.276
1.251
1. 228
1,270
1.600
1.562
1.526
1.491
1.457
1.426
1.396
1.366
1.338
1.312
1.286
1.261
1.237
1,280
1.612
1.574
1.538
1 502
1.469
1.437
1.407
1.377
1.348
1.322
1.296
1.271
1.247
1.625
1.586
1.549
1.514
1,480
1.448
1,417
1.387
1.359
1.332
1.306
1.280
1.256
98
TABLE VII. For reducing observations, etc. Continued.
a
Temperature of external air degrees Fahrenheit.
ii
1
5
20
10
10
20 1 30
40
50
60
70
80
90
100
H
1
1,300
1.637
.598
1.561
1.525
1.491
.459
1.428
1.398
.369
1.342
1.316
.290
1.266
1 310
I.G49
.610
1.573
.536
1.502
.470
1 439
1.408
.379
1.352
1. 326
.300
1.275
1,320
1.661
.622
1.584
.548
1.513
.481
1.449
1.419
.390
1.362
1.336
.309
1.285
1, 330
1.674
.634
1.596
.559
1.525
.492
1.460
1.429
.400
1.372
1.346
.319
1.294
1,340
1.686
.646
1.608
.571
1.536
.503
1.471
1.440
.410
1.382
1.356
.329
1.304
1,350
1.698
.658
1.620
.582
1.547
1.514
1.482
1.450
.420
1.393
1.366
.339
1.313
1,360
1.710
.669
1. 631
.593
1.558
1.524
1. 492
1.461
.431
1.403
1.375
.348
1.323
1,370
1.722
.681
1.643
.605
1.569
1.535
1.503
1.471
.441
1.413
1.385
.358
1.332
1,380
1.735
.693
1.655
.616
1.581
1.546
1.514
1.482
.451
1.423
1.395
.368
1.342
1,390
1.747
.705
1.666
.628
1.592
1.557
1.524
1.492
.462
1.433
1.405
.377
1.351
1,400
1.759
.717
1.678
.639
1.603
1.568
1.535
1.503
.472
1.443
1.415
.387
1.361
1,410
1.771
.729
1.690
.650
1.614
1.579
1.546
1.513
.482
1.453
1.425
.397
1.370
1,420
1.783
.741
1.701
.662
1.625
1.590
1.556
1. 524
.492
1.463
1.435
.406
.380
1,430
1.796
.753
1.713
.673
1.636
1.601
1.567
1.534
.503
1.473
1.444
.416
.389
1,440
1.808
1.765
1.724
.685
1.647
1.612
1.577
1.545
.513
1.483
1.454
.426
.399
,450
1. 820
1.777
1.736
,696
1.658
1.623
1.588
1.555
.523
1.493
1.464
1.436
.408
,460
1.832
1.788
1.748
.707
1.670
1.633
1.599
1.565
.533
1.503
1.474
1.445
.418
,470
1.844
1.800
1.759
.719
1.681
1.644
1.609
1.576
.543
1.513
1.484
1.455
.427
,480
1.857
1.812
1.771
.730
1.692
1.655
1.620
1.586
.554
1.523
1.493
1.465
1.437
,490
1.869
1.824
1.782
1.742
1.703
1.666
1.630
1.597
.564
1.533
1.503
1.474
1.446
1,500
1.881
1.836
1.794
1.753
1.714
1.677
1.641
1.607
1.574
1.543
1.513
1.484
1.45C
ITsTOEX.
Page.
Anemometer 51
Anemometer correction 52
Aneroid barometer 41
Application form for voluntary observers 11
Auroras, instructions for observing 61
Barometer, aneroid 41
changes of aneroid , 42
mercurial .' 30
cistern of 36
correction of observations 38
placing of 31
observation of : 32
reduction of observations to sea-level 96
reduction of reading to 32 94
reduction to sea-level 39
Beaufort scale 53
Bench-mark 59
Climate, general phenomena of 66
Clouds, classification 55
estimates of cloudiness 56
movement of 57
Coronse 60
Dew point 27
tables for 71
Directions, special, to observers -.. 67
Earthquakes 64
Evaporation 57
E vaporometer, Piche 58
Frost 60
Hygrometer, hair 30
Hypsometer 42
Instructions for use of tables 69
Maximum thermometer 18
error of 18
setting of 20
Marks on thermometer, replacing of 26
Mean temperature 24
Minimum thermometer 15
method of uniting column J6
placing thermometer 20
setting index 18
Percolation gauge 49
Piche evaporometer 58
9377 7 99
100
" ,.-* o - L ^ t ^ Page.
Psychromet^ ^ Ai". L C .C.. J"...-i.'.^t!L^. c 28
whirling of 29
wetting of muslin 29
Radiation thermometer, solar 25
Rainfall measurement 46
Rain gauge 43
instructions for use 44
support for 46
Relative humidity 28
tables for 81
River gauge 58
Sand spouts 61
Snowfall measurement 48
Tables, instructions for use of. 69
Thermometers 12
correction of 13
fall of freezing-point 14
maximum 18
minimum 15
packing for transportation 21
removal of air from column 14
replacing of marks 26
rise of freezing-point 13
shelter for 22
solar radiation 25
Thermoscope . . . ; 26
Thunderstorm 61
Tornadoes ; 61
Vapor of water in air 27
table of correction to pressure for reading of barometer 91
table of grains of vapor in cubic foot of air 93
table of pressure in inches 93
table of weight of vapor in air 93'
Weather, state of 60
Wind-vane 49
Vernier . . 25
LIST OF TABLES.
Table I. Dew point from wet and dry thermometer readings 71
II. Relative humidity , 81
III. Correction to vapor pressure for reading of barometer 91
IV. Vapor pressure in inches 92
V. Grains of water vapor in a cubic foot of air 93
VI. Reduction of barometer reading to 32 94
VII. Reduction of observations of barometer to sea-level 96
THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW
AN INITIAL FINE OF 25 CENTS
WILL BE ASSESSED FOR FAILURE TO RETURN
THIS BOOK ON THE DATE DUE. THE PENALTY
WILL INCREASE TO 5O CENTS ON THE FOURTH
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OVERDUE.
Gaylamount
Pamphlet
Binder
Gaylord Bros., Inc.
Stockton, Calif.
T. M. Reg. U.S. Pat. Off.
417958
U-
UNIVERSITY OF CALIFORNIA LIBRARY