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( JUN 24 26 % ) 



I 












































THE BAROMETER 

AS THE 

FOOT RUL^sin^ 

S / V OF THE (jUN 24 Q -'3 I 

s ^ Ay AIR 

mt Y 

By P. R. Jameson, F.R. Met . Soc., F.R.G.S. 



PUBLISHED BY 

TAYLOR INSTRUMENT COMPANIES 
Manufacturers of Meteorological Instruments 
Rochester, N.Y. U. S. A. 















































Copyrighted 1923 
by 

Taylor Instrument Companies 
Rochester, N. Y. 



T HE barometer, which only recently has come 
into popularity, was “invented” nearly three 
hundred years ago. 

The work in connection with this invention is 
very interesting. It seems that Galileo Galilei, an 
Italian Philosopher and mathematician (Born 1564- 
Died 1642), was asked toward the end of his life to 
explain why water could not be raised in a suction 
pump more than 32 feet. 

He was led to believe that nature’s abhorrence of 
a vacuum did not exceed the pressure of a column 
of water 32 feet high, but subsequently he devised 
an experiment to ascertain the power of a vacuum. 

His apparatus, which was placed in an inverted 
position, consisted of a tube with a very smooth in¬ 
terior, into which a piston was closely fitted. Weights 
were applied to this piston to see how much pull was 
necessary to draw the piston down. 

Previous to his death he recommended to his 
pupil (Evangelista Torricelli) that these experiments 
be continued. 

His decisive experiment was in ascertaining the 
length of a column of mercury sustained by the 
same cause, whatever it might be, which supported 
the column of water. 

As the weight of mercury is about fourteen times 
greater than that of water, he reasoned that 
the heights of the two should be proportional to 
their weights. 


3 































To prove his ideas on the subject, he took a glass 
tube about three feet in length, closed it at one end, 
and filled it with mercury. Putting his finger on 
the open end he inverted this tube in a small bowl, 
also containing mercury, and when he removed his 
finger, found that the mercury sank down in the 
tube until its level in the tube was about 29 
inches distant from the level of the mercury in 
the bowl. 

Torricelli continued his experiments and found 
the level of the mercury in the tube fluctuated as 
changes in the weather took place. As early as 
1645 he published his observations on this phe¬ 
nomenon. 

He died at Florence, Italy, October 25, 1647, be¬ 
fore his great discovery was fully completed. 

At this time a French author, Blaise Pascal, be¬ 
came interested in Torricelli’s discovery. His father 
had sent him to Paris for the study of languages, 
but the boy’s mind ran along mathematical lines 
and by the time he reached the age of 12 he was re¬ 
puted to be as far as the 32nd proposition of Euclid. 
His father, on discovering this, decided to give him 
a mathematical education. He soon became as¬ 
sociated with the scientific societies and astounded 
the most learned by his knowledge of mathematical 
problems. 

At the age of 16 he had invented a calculating 
machine, although it was never put to practical use. 
He also had completed the first wheel-barrow chair, 
a type of dray, and the hydraulic press. 

When 25 he started his barometrical experiments 
and confirmed the discoveries of Galileo, Torricelli, 
and others, regarding the weight of the air and its 
elasticity. It occurred to him that if the atmos¬ 
pheric pressure supported the mercury in the tube, 
as shown in Torricelli’s experiment, the height of 

4 


the column of mercury in the tube should increase 
or decrease if the pressure increased or decreased. 

He took up his ideas with Perier, his brother-in- 
law, who lived near the high conical mountain of 
Puy-de-Dome, and requested that he should test 
his theory upon this mountain. 

This was not accomplished until the autumn of 
1648. Perier manufactured two tubes, filled them 
with mercury and observed them, leaving one in 
his garden at Clermont, the height of the mercury 
in the tubes being 26 French inches and 3% lines. 

Leaving one behind to be observed during his ab¬ 
sence, he took the other up the Puy-de-Dome and 
at the summit observed that the mercury had fallen 
in the tube to 23 inches and 2 lines. Noting the 
tube as he returned he found at the lower levels of 
the mountain the mercury continued to rise until by 
the time he arrived in his garden at Clermont the 
mercury stood at its original level of 26 inches and 
3jk± lines. 

This was the first time observations had been 
made of air pressure in regard to elevations. 

Pleased at his success and confident that the 
ideas of Pascal had been proven correct, he repeated 
the experiment, going to the highest tower in Cler¬ 
mont. He communicated the results of his experi¬ 
ments to Blaise Pascal, who himself made similar 
observations, both from a high house and a belfry 
in Paris. 

Satisfied beyond measure with the results, he 
proposed this process as a means for determining 
the heights of any one place above another. Thus 
the “barometer” was born and sent on its career 
throughout the civilized world. 

The most distinguished men of science have 
worked to develop from this crude but original 
instrument of three hundred years ago, the fine in- 

5 


strument of the present day, but the modern in¬ 
strument is nothing but the original “tube inverted 
in a cup of mercury,” with many refinements. 

Patterns and styles have been many, the most 
ingenious and common pattern being the one op¬ 
erated by a mercury tube set in the back of a banjo¬ 
shaped frame, to which is fitted a dial divided in 
inches, bearing the very familiar but grossly inac¬ 
curate legends “Stormy,” “Fair,” and “Fine 
Weather,” over which an indicating hand travels. 

In 1798 M. Comte, Professor of Aerostatics in 
the school at Meudon near Paris invented a “watch¬ 
like, metallic, air-tight vacuum case, the lid of which 
sustained by internal springs, rises and falls under 
variable pressures.” This undoubtedly was the 
first “aneroid” (Greek compound “without fluid”) 
barometer and was made for the reason that in his 
balloon ascents he found the mercury barometer 
suffered greatly from violent oscillation. 


Barometer chamber before Barometer chamber after 

exhaustion exhaustion 

M. Vidi subsequently made a case of different 
form. He constructed a box with corrugations at 
the top and bottom to make it more elastic in its 
movements. When the air was withdrawn from 
this box it naturally collapsed at its centre. By a 
mechanical contrivance the two surfaces were made 
to open again by fitting studs to the upper and lower 
centre of each surface, pulling them apart, and me¬ 
chanically holding them open. Any increase in 
the pressure of the air, of course weighed down on 
this “box” or “chamber” and closed it slightly: 

6 















any decrease in pressure had the opposite effect, and 
allowed it to open. This movement was transmitted 
to a series of levers terminating at a small post or 
pin to which an indicating hand was fitted. A 
suitably engraved or figured dial enabled all changes 
in pressure to be fairly accurately and quickly read. 

This, when completed, made a very portable in¬ 
strument and at once sprung into popularity. It 
seems to have been further developed by English 
makers, and the result is that today there are made 
aneroid barometers constructed in such a manner 
as to show changes of as little as l-1000th of an inch 
of pressure. 

It has been the cause of much conjecture and a 
good deal of guessing on the part of many people 
how it is possible to know that a certain place is 
a certain number of feet above sea level. The writer 
once heard the remark, “They certainly cannot use 
tapes.’ ’ 

The invention of the aneroid type of instrument 
was of great importance since it would be out of the 
question to carry for any distance a large mercury 
barometer, at least 34 inches long, both cumbersome 
and unportable. 

Made, as they are, in sizes varying from about 
two inches for the tourist or traveller up to five 
inches for the surveyor, they are not only very port¬ 
able, but extremely accurate, providing they are not 
abused and are handled with ordinary care. 

The finer instruments are sensitive to almost a 
hair line and consequently very fine and accurate 
readings can be taken, providing the aneroid is 
properly and carefully constructed. 

The dials are divided into inches of mercury pres¬ 
sure and when we say the barometer is standing at 
“29” we mean that at that point of observation mer- 

7 


cury would be supported at a height of 29 inches 
in a tube, as explained in the Torricelli experiment. 



The pocket altitude barometer with 
unequally-divided altitude scale 


Before dealing with the barometer as a measurer 
of height it will be well to more thoroughly under¬ 
stand the air, the depth or height of which we at¬ 
tempt to measure. 

The first thing to remember is, that since air is 
elastic, it is more compressed, and therefore weighs 
heavier at the surface of the earth than at any 
point above it. 

The height of our atmosphere is not known. 
Nearly all authorities disagree on the subject. 

Never being able to view it from the top we can 
never be able to solve this problem. We are im¬ 
prisoned at the bottom of it. 

The opinion has gained ground that this air ocean 
reaches to a height of certainly two or three hundred 
miles—possibly four or five hundred—possibly a 
good deal more. 


8 










It is very difficult indeed to imagine the “top” of 
our atmosphere. The air shades off very gradually 
until it becomes the vacuum of space. This no 
living soul can explain, or even imagine. The 
thought of it is impossible. We, at the bottom of 
this great ocean of air, are as helpless in learning 
anything about the surface of it as is a flat fish at the 
bottom of the ocean of water in attempting to learn 
of its surface. 

The atmosphere of the sun is said to extend for 
500,000 miles—even this distance represents but 
a molecule of space, in the wonderful Universe. 

How helpless we are. The average person knows 
very little about the air a mile or so above his head, 
or its condition. Even when at that height he must 
fight for breath should he exert himself to any extent. 

These miles, maybe hundreds of miles of air, are 
pressing mightily downwards, packing tightly to¬ 
gether the lower layers of air near the earth’s surface. 
Here we live, right at the very bottom, and look on 
with wonder at the little mounds and heaps which 
we call mountains. True, they may be thousands of 
feet in height, but they are very small when compared 
to the depth of the air in which they are placed. 

The upper layers of this air must be lighter or 
“looser” in their construction for they do not have 
to support so much weight above. The greatest 
pressure is at the bottom. If we could cut the air 
up into slices of any size, each slice being equal to 
say half an inch of pressure, and pile them up thou¬ 
sands and thousands of feet into the air, the lower 
ones would be so squashed or compressed that they 
would not measure anywhere near the size of those 
above. Those toward the top would be nearer 
their original thickness and the very top one would be 
exactly the same size as it was before it was placed 
in position. 


9 



lipoo 

10,500 

20,000 

9.500 
9p00 
8J500 
8.000 

7.500 
7.000 

6.500 
6,000 

5.500 
5,000 

4.500 
4,000 

3.500 
3,000 
2500 
2,000 

2.500 
1,000 

500 

0 


22 . 00 " 


22.50 


2200 ' 


2250' 


23.00 1 


23.50 


24.00 


24.50 1 


25.00 


2550 


26.00 


2650' 


2700' 


2750’ 


2800' 


2850' 

f 

29.00' 


29.50' 


30.00 


3050 


3100 


ALTITUDE 

SCALE 


INCHES 

OF 

PRESSURE 


Perhaps this illustration can 
better be imagined if we use bales 
of cotton wool instead of blocks 
of air at a certain pressure. If 
the bales contained 100 pounds 
of cotton and were two feet thick, 
they would still contain 100 
pounds of cotton if by the 
weight of the thousands above 
them they were compressed to a 
thickness of only one foot. 

It is quite the same with the 
air. An inch of pressure at the 
level of the sea may be only 900 
feet thick, but an inch of pres¬ 
sure, high up in the air may be 
1500 feet thick. 

By this simple illustration it is 
quite easy to see that the dis¬ 
tances between each inch of 
pressure are not equal. A 
thousand feet of air is always a 
thousand feet of air, no matter if 
it is at a pressure of one inch or 
thirty inches. A foot rule is 
always the same length even 
though it be at the bottom of 
the sea, or on the summit of 
the highest mountain. The ex¬ 
periments of Blaise Pascal proved 
that if a barometer be taken up 
a mountain, hill or steeple, or to 
any place above a certain point, 
it will measure the difference in 
pressure between the first and 
last place of observation. 

Working pressure in inches. 


10 



























into feet of measurement, was an unhandy way of 
arriving at a result, and it remained for Sir George 
Biddell Airey, K. C. B., Astronomer Royal of Great 
Britain, to devise a scale of feet of measurement (see 
below) which exactly matched a scale of inches of 
pressure, to enable anyone to see the distance in feet 


Aneroid 
or Cor¬ 
rected 
Bar¬ 
ometer 

Height 

in 

Feet 

Aneroid 
or Cor¬ 
rected 
Bar¬ 
ometer 

Height 

in 

Feet 

Aneroid 
or Cor¬ 
rected 
Bar¬ 
ometer 

Height 

in 

Feet 

Aneroid 
or Cor¬ 
rected 
Bar¬ 
ometer 

Height 

in 

Feet 

Aneroid 
or Cor¬ 
rected 
Bar¬ 
ometer 

Height 

in 

Feet 

in. 

ft. 

in. 

ft. 

in. 

ft. 

in. 

ft. 

in. 

ft. 

31.00 

0 

28.28 

2500 

25.80 

5000 

23.54 

7500 

21.47 

10000 

30.94 

50 

28.23 

2550 

25.75 

5050 

23.50 

7550 

21.44 

10050 

30.88 

100 

28.18 

2600 

25.71 

5100 

23.45 

7600 

21.40 

10100 

30.83 

150 

28.12 

2650 

25.66 

5150 

23.41 

7650 

21.36 

10150 

30.77 

200 

28.07 

2700 

25.61 

5200 

23.37 

7700 

21.32 

10200 

30.71 

250 

28.02 

2750 

25.56 

5250 

23.32 

7750 

21.28 

10250 

30.66 

300 

27.97 

2800 

25.52 

5300 

23.28 

7800 

21.24 

10300 

30.60 

350 

27.92 

2850 

25.47 

5350 

23.24 

7850 

21.20 

10350 

30.54 

400 

27.87 

2900 

25.42 

5400 

23.20 

7900 

21.16 

10400 

30.49 

450 

27.82 

2950 

25.38 

5450 

23.15 

7950 

21.12 

10450 

30.43 

500 

27.76 

3000 

25.33 

5500 

23.11 

8000 

21.08 

10500 

30.38 

550 

27.71 

3050 

25.28 

5550 

23.07 

8050 

21.05 

10550 

30.32 

600 

27.66 

3100 

25.24 

5600 

23.03 

8100 

21.01 

10600 

30.26 

650 

27.61 

3150 

25.19 

5650 

22.98 

8150 

20.97 

10650 

30.21 

700 

27.56 

3200 

25.15 

5700 

22.94 

8200 

20.93 

10700 

30.15 

750 

27.51 

3250 

25.10 

5750 

22.90 

8250 

20.89 

10750 

30.10 

800 

27.46 

3300 

25.05 

5800 

22.86 

8300 

20.85 

10800 

30.04 

850 

27.41 

3350 

25.01 

5850 

22.82 

8350 

20.82 

10850 

29.99 

900 

27.36 

3400 

24.96 

5900 

22.77 

8400 

20.78 

10900 

29.93 

950 

27.31 

3450 

24.92 

5950 

22.73 

8450 

20.74 

10950 

29.88 

1000 

27.26 

3500 

24.87 

6000 

22.69 

8500 

20.70 

11000 

29.82 

1050 

27.21 

3550 

24.82 

6050 

22.65 

8550 

20.66 

11050 

29.77 

1100 

27.16 

3600 

24.78 

6100 

22.61 

8600 

20.63 

11100 

29.71 

1150 

27.11 

3650 

24.73 

6150 

22.57 

8650 

20.59 

11150 

29.66 

1200 

27.06 

3700 

24.69 

6200 

22.52 

8700 

20.55 

11200 

29.61 

1250 

27.01 

3750 

24.64 

6250 

22.48 

8750 

20.51 

11250 

29.55 

1300 

26.96 

3800 

24.60 

6300 

22.44 

8800 

20.47 

11300 

29.50 

1350 

26.91 

3850 

24.55 

6350 

22.40 

8850 

20.44 

11350 

29.44 

1400 

26.86 

3900 

24.51 

6400 

22.36 

8900 

20.40 

11400 

29.39 

1450 

26.81 

3950 

24.46 

6450 

22.32 

8950 

20.36 

11450 

29.34 

1500 

26.76 

4000 

24.42 

6500 

22.28 

9000 

20.32 

11500 

29.28 

1550 

26.72 

4050 

24.37 

6550 

22.24 

9050 

20.29 

11550 

29.23 

1600 

26.67 

4100 

24.33 

6600 

22.20 

9100 

20.25 

11600 

29.17 

1650 

26.62 

4150 

24.28 

6650 

22.16 

9150 

20.21 

11650 

29.12 

1700 

26.57 

4200 

24.24 

6700 

22.11 

9200 

20.18 

11700 

29.07 

1750 

26.52 

4250 

24.20 

6750 

22.07 

9250 

20.14 

11750 

29.01 

1800 

26.47 

4300 

24.15 

6800 

22.03 

9300 

20.10 

11800 

28.96 

1850 

26.42 

4350 

24.11 

6850 

21.99 

9350 

20.07 

11850 

28.91 

1900 

26.37 

4400 

24.06 

6900 

21.95 

9400 

20.03 

11900 

28.86 

1950 

26.33 

4450 

24.02 

6950 

21.91 

9450 

19.99 

11950 

28.80 

2000 

26.28 

4500 

23.97 

7000 

21.87 

9500 

19.95 

12000 

28.75 

2050 

26.23 

4550 

23.93 

7050 

21.83 

9550 

19.241 

13000 

28.70 

2100 

26.18 

4600 

23.89 

7100 

21.79 

9600 

18.548 

14000 

28.64 

2150 

26.13 

4650 

23.84 

7150 

21.75 

9650 

17.880 

15000 

28.59 

2200 

26.09 

4700 

23.80 

7200 

21.71 

9700 

17.235 

16000 

28.54 

2250 

26.04 

4750 

23.76 

7250 

21.67 

9750 

16.615 

17000 

28.49 

2300 

25.99 

4800 

23.71 

7300 

21.63 

9800 

16.016 

18000 

28.43 

2350 

25.94 

4850 

23.67 

7350 

21.59 

9850 

15.439 

19000 

28.38 

2400 

25.89 

4900 

23.62 

7400 

21.55 

9900 

14.883 

20000 

28.33 

2450 

25.85 

4950 

23.58 

7450 

21.51 

9950 




11 


































they had travelled by subjecting their aneroid barom¬ 
eter to the pressure at a certain place and to that of 
one above it. 

In March 1867 he presented this scale to the 
“Royal Society of England,” who passed upon it, 
and it seems to have been immediately adopted by 
English manufacturers, being in general use up to 
the present day. 

As a zero, or starting point, for the scale of feet 
had to be determined, he selected the thirty-one- 
inch point, as the barometer at sea level never, or at 
least very rarely, indicated a pressure of air greater 
than this. Made in this way he assumed that the 
hand of the barometer would always be at some 
point on the new scale of altitudes he had devised. 

It is oftentimes wondered why the altitude zero 
was not started from thirty inches. The answer is 
quite simple for if the barometer stood at some point 
higher than thirty inches (and it frequently does) 
the hand would be off the altitude scale and conse¬ 
quently no reading on it would be possible. 

This scale had to be universal and had to be con¬ 
sidered from the lowest point on land, which is sea 
level, since the height of any town, river or mountain 
is understood to be “so many feet above sea level.” 

Tourists are ofttimes greatly disappointed in 
viewing high mountains or peaks, to see them so 
apparently small. 

When in Colorado, I well remember hearing a per¬ 
son at Pike’s Peak for the first time exclaim, “Why, 
I was told this Peak was over 14,000 feet high!” 
He little thought that the Peak itself rises but 8,000 
feet above Colorado Springs, and that Colorado 
Springs is 6,000 feet above sea level. He evidently 
expected to find a towering mountain rising 14,000 
feet in the air, instead of 14,000 feet from the level 
of the sea. 


12 



In computing 
this scale it was 
found that the 
inch of pressure 
between “30” 
and “31” is 890 
feet in thickness 
—small because 
it is compressed by the very great weight of all 
above it. Between the inches “17” and “18” the 
distance was found to be 1580 feet, much greater 
because at that height (approximately 14,000 feet) 
the air is much lighter, since it is not compressed by 
so much above. 

An altitude scale was thus devised and was ac¬ 
cepted as correct at a temperature of 50° Fahren¬ 
heit. Mention of temperature in connection with 
this is made for the reason that air can be expanded 
or contracted by either increasing or decreasing its 
temperature. If 
the temperature 
is lowered, one 
inch of pressure 
shrinks a trifle in 
depth, and if the 
temperature be 
increased it be- 

trifle 



ipoo 

ir>( 

OIL 

1 

iL 

i 


rTT' 

Uil-- 



M 




XT 



comes 


a 


17" to 18" represents 1,580 ft. 


deeper. If we seal 

a tin and heat it, the air inside expands and breaks 
open the tin. 

The “altitude” and “inches of pressure” scales 
do not match one another; that is, they are not 
equal and as they were originally computed with the 
31-inch point as the zero, they become incorrect 
when used in any other manner, unless the altitude 
scale is manufactured in the new and improved way, 


13 
























viz., in equal divisions, which makes it correct when 
revolved to the point of the hand. 

In manufacturing the mechanism for an aneroid 
barometer and arranging it to agree with the standard 
mercurial barometer, the natural order of things was 
usually reversed, that is, the pressure scale was 
divided in equal divisions, instead of being in unequal 



* Internal mechanism’of modern altitude barometer 


divisions as in nature, which, consequently, makes the 
altitude scale of divisions unequal, that really in nature 
are equal. In value they are exactly the same, that 
is, the unequal divisions of the one match the equal 
divisions of the other exactly, and are as correct as 
they would be if made and engraved according to 
nature. As noted in a previous paragraph, the new 
method is to make the altitude scale in equal divisions. 

The old type of aneroid had its altitude scale 
sometimes engraved on the same plate as that on 
which the pressure or inch scale appeared. At other 
times these scales were made to revolve. 


* For full and detailed description of the construction and manufacture of this see 
“Practical Hints for Amateur Weather Forecasters2nd Edition, by P. R. Jameson. 




A revolving scale of this type is obviously incorrect 
and likely to be grossly misleading when in the hands 
of a novice, for it is quite natural for a person not 
thoroughly conversant with the instrument to turn 
the scale around until the “0” feet on the altitude 
scale is in a line with and directly under the point of 
the hand, before starting on a trip up a mountain or 
hill, naturally thinking one had to start from “zero” 
or “0” feet. 

The result of this would be that the hand would 
start to move in that part of the altitude scale 
which showed the widest division. As an instance, 
the value of the altitude scale between 28 inches and 
27 inches is approximately 1000 feet, so if at the 
start of an observation the hand stood at 28 inches 
(represented on the altitude scale by 2750 feet) and 
at the termination of the climb at 27 inches (repre¬ 
sented on the altitude scale by 3750 feet) the height 
between the two places would be the difference be¬ 
tween the two readings; viz., 3750-2750=1000. 

Now, if the scale be revolved until the “0” feet 
upon it stood directly beneath the hand at 28 inches, 
and the hand travelled during the ascension of the 
hill until it pointed to the 27-inch point, the altitude 
shown by the scale would be but 890 feet, or in error 
to the extent of 110 feet! 

The cause of this, as explained before, is that the 
wrong part of the altitude scale was used in connec¬ 
tion with a certain pressure. 

The “0” feet of the altitude scale and the “31- 
inch” of pressure point, must always be coincident 
if correct readings are desired on this type. There is 
no other way to use this barometer correctly. 

With the new type of instrument the revolving 
altitude scale is divided in equal divisions and the 
“0” feet can be set at the hand, the ascent started 
and the altitude at any time read correctly off the 

15 





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dial, at the wish of the user. It is of great convenience 
and a marked advancement in instrument making. 

It is popularly believed that an altitude barometer 
will give the observer information as to the height 
he is above sea level, by simply observing its dial. 
This it cannot do. 

Altitude barometers 
simply indicate the 
height between one 
place of observation and 
another. They are prac¬ 
tically rules, or meas¬ 
ures, put up in a differ¬ 
ent form but designed 
for the same purpose. 

We realize the utter 
absurdity of endeavor¬ 
ing to find the altitude 
of a place at which we 
may bestanding, by con¬ 
sulting aruler. Itisquite 
as absurd to expect to 
obtain this information 
by looking at the dial of 
an aneroid barometer. 

The Geological Sur¬ 
vey, U. S. Weather 
Bureau, U. S. Coast and 
Geodetic Survey, U. S. 

Geographic Survey, U. , . ^ J , , 3 , u 

° . 1 J 7 Extra-high-grade pocket altitude barometer 

S. Engineer Corps, U.S. with certificate of errors and equally- 

Lake Survey, U. S. divided altitude scale 

Army, Geological Surveys of different States, Rail¬ 
roads, City Engineers, Clubs, and many individuals 
have established the elevation of different points above 
sea level over the whole country and their findings are 
on record in a volume of over a thousand pages. 

16 























If it be necessary to find the elevation of a certain 
place above sea level, it is of course, necessary to 
start at, or near, one of these ‘‘bench marks ” first 
noting its height above sea level and then determin¬ 
ing by the aneroid barometer the difference in 
height between the “bench mark” and the second 
point of observation. 

If, for instance, we were at Helena, Montana, we 
would find on the City Hall a mark “4108 feet above 
sea level.” Supposing we wanted to find the dif¬ 
ference in elevation between Helena and Boulder, 
Montana, we would observe our barometer at 
Helena before starting. It might read at say 25.80 
inches, equivalent to the 5,000-feet mark on the alti¬ 
tude scale. On arriving at Boulder, (Northern 
Pacific Railway) it would point to approximately 
25.03 inches, equivalent to the 5815 feet on the alti¬ 
tude scale. The difference between the two readings 
is 5815 minus 5000 feet, or 815 feet. 

Before starting we found the bench mark at 
Helena to be 4108 feet above sea level, so if we add 
this 4108 feet to the difference in elevation between 
Helena and Boulder we get the height of Boulder 
above sea level. Our finding is 4108 plus 815, equals 
4923 feet. 

In a previous paragraph mention was made of the 
effect of temperature on the air. The correction for 
this is laid out in the two tables (pages 18 and 19) 
taken from the Smithsonian Miscellaneous Collection. 

These tables need not be taken into consideration 
unless very accurate readings are required. 

As an instance, suppose at the bottom of a moun¬ 
tain the temperature was 70° Fahrenheit and the hand 
on the barometer pointed at 2,000 feet. The correction 
as noted at 70° Fahrenheit is 82 feet, which has to be 
added as have all temperature corrections above 50° 
Fahrenheit, making the indication 2082 feet. 

17 


TEMPERATURE CORRECTIONS FOR ALTITUDE SCALES 

Smithsonian Miscellaneous Collection No. 21. 

F'or temperatures above 50° F. the values are to be added. 

For temperatures below 50° F. the values are to be subtracted. 


FEET OF ALTITUDE 


Fahrenheit 

100 

500 

1000 

2000 

3000 

49° 

51° 

0 

1 

2 

4 

6 

48° 

52° 

0 

2 

4 

8 

12 

47° 

53° 

1 

3 

6 

12 

18 

46° 

54° 

1 

4 

8 

16- 

24 

45° 

55° 

1 

5 

10 

20 

31 

44° 

56° 

1 

6 

12 

24 

37 

43° 

57° 

1 

7 

14 

29 

43 

42° 

58° 

2 

8 

16 

33 

49 

41° 

59° 

2 

9 

18 

37 

55 

40° 

60° 

2 

10 

20 

41 

61 

39° 

61° 

2 

11 

22 

45 

67 

38° 

62° 

2 

12 

24 

49 

73 

37° 

63° 

3 

13 

27 

53 

80 

36° 

64° 

3 

14 

29 

57 

86 

35° 

65° 

3 

15 

31 

61 

92 

34° 

66° 

3 

16 

33 

65 

98 

33° 

67° 

3 

17 

35 

69 

104 

32° 

68° 

4 

18 

37 

73 

110 

31° 

69° 

4 

19 

39 

77 

116 

30° 

70° 

4 

20 

41 

82 

122 

29° 

71° 

4 

21 

43 

86 

128 

28° 

72° 

4 

22 

45 

90 

135 

27° 

73° 

5 

23 

47 

94 

141 

26° 

74° 

5 

24 

49 

98 

147 

25° 

75° 

5 

25 

51 

102 

153 

24° 

76° 

5 

27 

53 

106 

159 

23° 

77° 

6 

28 

55 

110 

165 

22° 

78° 

6 

29 

57 

114 

171 

21° 

79° 

6 

30 

59 

118 

177 

20° 

80° 

6 

31 

61 

122 

184 

19° 

81° 

6 

32 

63 

126 

190 

18° 

82° 

7 

33 

65 

130 

196 

17° 

83° 

7 

34 

67 

135 

202 

16° 

84° 

7 

35 

69 

139 

208 

15° 

85° 

7 

36 

71 

143 

214 

14° 

86° 

7 

37 

73 

147 

220 

13° 

87° 

8 

38 

75 

151 

226 

12° 

88° 

8 

39 

77 

155 

232 

11° 

89° 

8 

40 

80 

159 

239 

10° 

90° 

8 

41 

82 

163 

245 

9° 

91° 

8 

42 

84 

167 

251 

8° 

92° 

9 

43 

86 

171 

257 

7° 

93° 

9 

44 

88 

175 

263 

6° 

94° 

9 

45 

90 

179 

269 

5° 

95° 

9 

46 

92 

184 

275 

4° 

96° 

9 

47 

94 

188 

281 

3° 

97° 

10 

48 

96 

192 

287 

2° 

98° 

10 

49 

98 

196 

294 

1° 

99° 

10 

50 

100 

200 

300 

0° 

100° 

10 

51 

102 

204 

306 


4000 


18 


OoCi-‘t«'Ji^l'Of-CA)»t'OOoCKJ>l ; *tnM'O^CAi^aOOCtOtl i O\OOOh J C*iC^MvOOtOit*0'OOOts)C>Jtn'J'OH-‘C*i4 i (7'00 
























TEMPERATURE CORRECTIONS FOR ALTITUDE SCALES 

(Continued) 

Smithsonian Miscellaneous Collection No. 21. 

For temperatures above 50° F. the values are to be added. 

For temperatures below 50° F. the values are to be subtracted 


FEET OF ALTITUDE 


Fahrenheit 

5000 

6000 

7000 

8000 

9000 

10000 

49° 

51° 

10 

12 

14 

16 

18 

20 

48° 

52° 

20 

24 

29 

33 

37 

41 

47° 

53° 

31 

37 

43 

49 

55 

61 

46° 

54° 

41 

49 

57 

65 

73 

82 

45° 

55° 

51 

61 

71 

82 

92 

102 

44° 

56° 

61 

73 

86 

98 

110 

122 

43° 

57° 

71 

86 

100 

114 

128 

143 

42° 

58° 

82 

98 

114 

130 

147 

163 

41° 

59° 

92 

110 

128 

147 

165 

184 

40° 

60° 

102 

122 

143 

163 

184 

204 

39° 

61° 

112 

135 

157 

179 

202 

224 

38° 

62° 

122 

147 

171 

196 

220 

245 

37° 

63° 

133 

159 

186 

212 

239 

265 

36° 

64° 

143 

171 

200 

228 

257 

285 

35° 

65° 

153 

184 

214 

245 

275 

306 

34° 

66° 

163 

196 

228 

261 

294 

326 

33° 

67° 

173 

208 

243 

277 

312 

347 

32° 

68° 

184 

220 

257 

294 

330 

367 

31° 

69° 

194 

232 

271 

310 

349 

387 

30° 

70° 

204 

245 

285 

326 

367 

408 

29° 

71° 

214 

257 

300 

343 

385 

428 

28° 

72° 

224 

269 

314 

359 

404 

449 

27° 

73° 

234 

281 

328 

375 

422 

469 

26° 

74° 

245 

294 

343 

391 

440 

489 

25° 

75° 

255 

306 

357 

408 

459 

510 

24° 

76° 

265 

318 

371 

424 

477 

530 

23° 

77° 

275 

330 

385 

440 

495 

551 

22° 

78° 

285 

343 

400 

457 

514 

571 

21° 

79° 

296 

355 

414 

473 

532 

591 

20° 

80° 

306 

367 

428 

489 

551 

612 

19° 

81° 

316 

379 

442 

506 

569 

632 

18° 

82° 

326 

391 

457 

522 

587 

652 

17° 

83° 

336 

404 

471 

538 

606 

673 

16° 

84° 

347 

416 

485 

555 

624 

693 

15° 

85° 

357 

428 

500 

571 

642 

714 

14° 

86° 

367 

440 

514 

587 

661 

734 

13° 

87° 

377 

453 

528 

604 

679 

754 

12° 

88° 

387 

465 

542 

620 

697 

775 

11° 

89° 

398 

477 

557 

636 

716 

795 

10° 

90° 

408 

489 

571 

652 

734 

816 

9° 

91° 

418 

*502 

585 

669 

752 

836 

8° 

92° 

428 

514 

599 

685 

771 

856 

7° 

93° 

438 

526 

614 

701 

789 

877 

6° 

94° 

449 

538 

628 

718 

807 

897 

5° 

95° 

459 

551 

642 

734 

826 

918 

4° 

96° 

469 

563 

657 

750 

844 

938 

3° 

97° 

479 

575 

671 

767 

862 

958 

2° 

98° 

489 

587 

685 

783 

881 

979 

1° 

99° 

500 

599 

699 

799 

899 

999 

0° 

100° 

510 

612 

714 

816 

918 

1020 


19 





















iM. 



If at the summit the hand points to 6,000 feet and 
the temperature is 20° Fahrenheit the correction will 
be 367 feet to be subtracted, making our elevation 
5633 minus 2082, or 3551 feet. 

This illustration shows a range of 50° Fahrenheit 
in temperature on an elevation of 4,000 feet, so the 
correction is naturally a large one. 

Altitude scales are ordinarily made to register from 
3,000 feet to 25,000 feet around their circumference. 
Naturally those reading to 3,000 feet are divided in¬ 
to finer divisions 
than those of 
higher altitude. 

Certain types 
of barometers 
are constructed 
to allow a very 
fine subdivision 
of their altitude 
scales. In order 
to make this 
possible their 
mechanisms are 
altered so that 
the altitude scale 
can be divided 
into equal parts 
and the pres¬ 
sure scale into 
unequal parts, 
just as in nature. 

A vernier rotates around their circumference and by 
its use it is possible to read to single feet of elevation. 

The vernier was invented by a* Brussels engineer, 
Peter Vernier, in 1631—quite a few years before the 
barometer was invented. It really consists of a 
movable scale attached to a fixed scale, to measure 


Altitude barometer as used by surveyors. Reads to 
single feet of altitude. 


20 






















spaces smaller than those into which the fixed scale 
is actually divided. 

The vernier will be easily understood if the figure 
illustrated be explained. The scale upon which the 
figures 2000 appear represents part of a scale of al¬ 
titude, divided into tenths and subdivided into 



hundredths, so that each of the smaller divisions 
represent 10 feet. The smaller scale above, marked 
‘'ascent,” represents the vernier and is movable 
around the other scale. The ten lines on the vernier 
scale exactly cover twenty-one divisions on the alti¬ 
tude scale, consequently each division of the vernier 
covers 2 l-10th divisions of the altitude scale. 

If the "0” were to be moved around until it co¬ 
incided exactly with the 2000 division, the first line 
on the vernier scale would point to the 2 l-10th di¬ 
vision, the second to 4 2-10, the third to 6 3-10, the 
fourth to 8 4-10, the eighth to 16 8-10, the ninth to 
18 9-10, and the tenth to 20 10-10 or 21. 

It is clear that but one division on the vernier can 
coincide with a division on the fixed scale, at one time. 
The lines that exactly coincide mark the subdivision 
of the division. 

The illustration shows the u 0” at a point 1770 
(imagining the scale be extended to the right so 
that the 1000 is perceptible) while the seventh line 
of the vernier scale is in alignment with the line on 
the fixed scale, making the true reading 1777. 

21 









THE EFFECT OF WEATHER CHANGES ON 
THE ALTITUDE SCALE 


As the weight of the air is not constant in any one 
place, it frequently happens that a change in the 
weather (either an increase or decrease in air pressure) 
takes place during a long ascent of a mountain, which 
causes the hand of the barometer to travel either 
down or up the altitude scale. 

This change in air pressure can of course, be easily 
mistaken for an increase or decrease in the height 
travelled by the observer. 

As an instance, let us suppose we remained at a 
certain point for twelve hours and that when we ar¬ 
rived the barometer showed 1200 feet on its alti¬ 
tude scale and when we departed 1300 feet. It is 
certain we had not risen 100 feet, for we remained at 
the same point. 

The change in reading of the scale is due to a 
change in atmospheric pressure, probably indicating 
the approach of a change in the weather. 

Variations of this character are usually very small 
and extend over a good many hours, so for ordinary 
purposes they can be disregarded, but, when travel¬ 
ling it is advisable to note the point at which the 
barometer stands at night, so if by morning any 
change has taken place it can be taken care of. 

Engineers, surveyors, and others who need to 
take very exact readings, usually employ either an 
observer at the point they leave, to read another ba¬ 
rometer hourly and note its changes, or else they use 
a “ Stormograph ” (recording barometer) so all the 
changes are automatically noted on a chart both as 
to the time such changes occur and their amount. 

Note of the time they arrive at certain points and 
the reading of the barometer with them is made, so 
when they return to their starting point or base, by 

22 


consulting the “Stormograph” they can determine the 
exact amount to deduct from or add to their reading 



Here is a simple example. Suppose a party 
started out at 8 a. m. on Monday with their barom¬ 
eters reading at 29.50 inches, the equivalent of 
1350 feet on the altitude scale. By 10 p. m. the 
summit of a mountain had been reached and their 
barometer read 24.20 inches, the equivalent of 6750 
feet on the scale. They would naturally compute 
their altitude in feet as 6750 minus 1350, equals 5400 
feet. After resting the night they retraced their 
footsteps, arriving at their starting point any time 
on the following evening (Tuesday) having been 
away for approximately thirty-six hours. 

By referring to their “Stormograph” record they 
find that at 10 p. m. Monday the barometer stood 
at 29.70 inches. (When they left it was reading 
29.50 inches.) 

Now we see that at their base at 10 p. m. Monday 
the barometer read 29.70 inches, equal to 1150 feet 
on the altitude scale, and at the summit 24.20 inches, 
the equivalent of 6750 feet on the altitude scale, so 
the reading is 6750 minus 1150, or 5600 feet altitude. 

23 



























WEATHER SERIES FOR THE AMATEUR 

By P. R. Jameson, F.R. Met. Soc., F.R.G.S. 

Practical Hints for Amateur Weather Forecasters.” Second and enlarged 
edition. Twenty-four pages, illustrated. Information on care of ba¬ 
rometers, how set for sea level, effect of temperature on weather, etc., 
Beaufort’s wind scale, and approximate forecast for the whole of the 
barometer scale, for rising or falling indications. 

Humidity, Its Effect on our Health and Comfort.” Twenty-four pages, 
illustrated, on matters concerning the necessity of correcting inside 
moisture conditions, which are dangerous to health and deprive us of 
comfort. Hygrometer and dew point tables included in this book. 

The Mountains of Cloudland and Rainfall.” Twenty-four pages, illus¬ 
trated with different types of clouds and rain gauges. The matter of rain¬ 
fall is dealt with concisely. Information given on variety and speed of 
clouds, with elevations. Different specimens are described, so it is easy 
for any one to recognize them quickly. 

The Thermometer and Its Family Tree.” Twenty-four pages, illustrated 
with thermometers from the time of their invention to the present day. 
Birth and development of this instrument is popularly dealt with and the 
different scales in use on all types are clearly described. The manufacture 
of thermometers is described in plain language. 

The Barometer as the Foot Rule of the Air.” Twenty-four pages, illus¬ 
trated. An elementary booklet describing the invention of the barometer 
and the processes it has gone through to bring it to its present status. 
Information as to correct method of using barometers to measure heights, 
corrections necessary for absolute readings, etc. 

The Compass, The Guidepost of the World.” Twenty-four pages, illus¬ 
trated. History of the Compass, its invention and use, is clearly given. 
A map giving declination of the compass for all parts of the United States 
is also included. 

Any of above, 15 cents postpaid, stamps or silver 

Weather and Weather Instruments.” Second and Revised Edition. 164 
pages, illustrated. Written in the unscientific language of the layman, 
conveying a clear idea of this subject to anyone of ordinary mental 
capacity. Chapters on clouds, fogs, weather map, frost, dew, snow, rain, 
barometers, humidity, thunder, etc., etc. 

Cloth cover $1.00 ; paper cover 50c postpaid, stamps or silver