Gilbert Weather Bureau - Part
44 GILBERT BOY ENGINEERING
NOTE: This book was published around 1920 as a
manual to accompany the Gilbert Weather Bureau sets.
The sets and manual were part of the "Boy Engineering"
series, While some of the experiments and activities here
may be safely done as written, some of them may be considered
hazardous in today's world, such as handling a mercury
barometer. In addition, some of the information
contained in this book is either outdated
or inaccurate. Therefore, this book is probably
best appreciated for its historical value rather than as a
source for current information and good experiments. If
you try anything here, please understand that you do
so at your own risk. See our Terms of
Pages 44 - 61
NOTE: Many figures have been
relocated from their position in the printed text to make them
more readable on a web page. This may or may not be
indicated in the text.
When overhead clouds are thick and grayish and the lower surface of
them is lumpy, this is an indication of rain.
Whirlwinds of dust are also indications of rain.
The rings that we see formed about the moon are cause by the
delicate white clouds through which the moon is shining.
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The morning rainbow indicates that a shower is in the west, but if
the rainbow is in the east it indicates that the shower has passed
There are certain actions of birds that indicate many things
pertaining to the weather that are interesting. It is probable
that their ability to fly into the air gives them a view of the
horizon, that by instinct they have been able to determine the
atmospheric changes. For instance, it is well known that if
birds of long flight remain at their base, it generally foretells a
stone. The sudden silence of birds has been referred to a
great many times preceding a storm.
Barnyard fowls do many peculiar things that foretell certain weather
conditions. The crow flies low and in great circles, cawing
loudly, before approaching rain.
Sometimes the housefly is a pretty good barometer. Generally
before a storm they seem to light on everything, particularly
persons, and we call them "sticky." Generally at these times
they congregate in swarms. Most everyone is familiar with the
gnat. They are one of the few insects that give us indications
and good signs, and when you see them forming in groups and moving
along in front of you, you may expect fair weather.
There are many other interesting facts and fairy tales about
indications by animals and insects, but there's nothing scientific
about them. It has been demonstrated that there is nothing
conclusive to be drawn from such signs, so we will not attempt to
waste pages of this book reiterating these fables.
Certain actions of insects and animals give indications and enable
the weather prophet to prophesy. The spider is a good example
of an insect prophet, and if you will observe him carefully, you
will find that when stormy weather is going to come on he shortens
his webs, and if he anticipates a long, hard storm, he not only
shortens the strings that hold up the web, but strengthens them as
well, and vice-versa, when he anticipates fine weather, he lengthens
his strands of web. When you see the spider cease his
activities and he hangs pretty close to his home, which is the
center of the web, you will know that rain is approaching. On
GILBERT BOY ENGINEERING
hand, if he continues to spread about during a storm, you can be
pretty certain that it is not going to be of very long
The frog is a good example of an animal prophet. There is a
green frog which has been studied in Germany, which will come out of
the water when rainy weather or cold is approaching. Some
observers have placed these frogs in a glass jar with a landing
provided so that he can come out of the water when he wants to, and
he is always observed high and dry above the water several hours in
advance of a storm.
Forecasting Weather by Means of
The first part of this book may not appeal to you, if you are of a
scientific trend of mind, but it is quite essential that you possess
a knowledge of the fundamentals treated in the earlier pages in
order to thoroughly understand the weather instruments we will now
describe. These instruments are the scientific means of
forecasting what the weather is going to be. They definitely
indicate certain things, and from these indications you are going to
be able to draw conclusions and become a scientist or
meteorologist. The success that you attain will depend upon
the accuracy of the instruments and the care you use in reading
them. You will be able to rig up a Weather Bureau of your own,
and the use of these instruments will interest anyone in a study of
To make a forecast, it is essential from what we have already
written to know the direction of the wind, and to determine the
direction we must have a weather vane. It is real important
that the vane should be sensitive to the slightest movement of the
wind and give actual wind directions. At the same time it must
possess the property of steadiness, so that when it is set up it
will be rigid.
Fig. 34 shows the standard weather vane used at all United States
Weather Bureau Stations and Fig. 35 shows the Gilbert Weather
Fig. 35. The Gilbert weather vane consists of a metal arrow
pointer and a metal rod 8 inches long and five thirty-seconds
WEATHER BUREAU 47
of an inch in diameter. The rod is fastened by means of a few
staples to the side of a pole, or whatever is to be used as a
support for the vane. About three inches from the top is a
collar with set screw, which is tightened, and the vane itself is
then placed on the rod, the rod passing through the small angles A
and B, between the sides of the vane. It will be found that
the vane will swing freely on this support, and by constructing two
crosspieces, with letters N, S, E, and W at each end of the pieces,
of course having N pointing directly north, the vane will swing
around and show the direction of the wind.
The standard United States Weather Bureau type hardly needs
explanation, as the illustration clearly shows all the parts.
It is the old, reliable, standard iron, combined wind vane and
anemometer support complete, twenty feet high; iron contact box near
base, improved roller bearings for six foot vane; latter, with
electrical contacts shown enlarged at the right. The vane is
fastened securely to the roof of the building and held in a
perfectly vertical position.
ANEMOMETER. Fig. 36
It is essential to know the velocity of the wind. This is
determined by means of an instrument called the anemometer.
Fig. 36. The Standard U.S. Weather Bureau Station Anemometer.
This is the well-known standard Robinson Anemometer, now in
universal use throughout the world for the registration of wind
velocity, but of the latest improved construction. It records
electrically the miles or kilometers, etc., of wind movements on a
register. The standard pattern as furnished to Weather Bureau
stations is made of brass, highly polished and finished, aluminum
(or copper reinforced) cups, steel spindle with hard steel bearings,
a ten-mile or kilometer indicator, electrical contacts etc.
The four hollow hemisphericical cups are mounted 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 a
screw. This 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. The mechanisms are mounted in a suitable metal case
with glass front,
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[Originally contained Fig. 39]
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as shown in the illustration, well protected from the weather, the
whole being designed for outdoor use.
The center of the cups moves with a velocity about one-third that of
the wind which puts them in motion. The cups are four inches
in diameter. The distance from the center of cup to center of
rotation or axis is 6.72 inches. Assuming that the wind-travel
is exactly three times that of the center of the cup, the dials are
marked to register miles of wind travel, five hundred revolutions 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 higher
than low velocities. It also varies with the dimensions of the
instrument, being different for every different length of arm and
diameter of cup.
On account of the great interference offered by buildings and other
obstructions to the free movement of the wind, its velocity is much
less in the vicinity of these obstructions than beyond; therefore,
in selecting the location for an anemometer, preference should be
given to the more elevated points in the vicinity of the station,
and some rigid support should be used to raise the instrument as far
as practicable above the immediate influence of the office building
itself. The support must be set up so that the anemometer on
top or on the cross-arm is as nearly vertical as possible.
The illustration shows clearly the appearance of an improved Weather
Bureau pattern combined support for wind instruments, similar to the
one installed at our plant.
WEATHER BUREAU 51
Fig. 37. The Gilbert Anemometer.
The Gilbert Anemometer consist of a case containing a spindle
passing through a worm gear, which turns a toothed gear. This
gear in its rotary motion makes a contact with a brass brush, which
is connected electrically with a flashlight. The cross arms,
with cups attached, is placed on the spindle, and as the wind blows,
it revolves the cups, causing the contact. The velocity of the
wind is determined by counting the flashes for fifteen seconds, thus
giving you the number of miles per hour. For instance, if a
light flashes eight times in fifteen seconds, this signifies that
the wind is blowing 8 miles an hour.
Fig. 38. How to Connect the Gilbert Anemometer.
By referring to the diagram, you will see that one wire which should
be the annunciator wire, or even a small electric light wire, is
connected from the wire at the anemometer case directly to one side
of the lamp socket. Another piece of the same size wire
connects the other side of the lamp socket to one terminal of your
switch. The second terminal of the switch should be connected
to an outer post of one dry battery. The inner post of this
same dry battery should be connected to the outer post of the second
dry battery. Complete the circuit by connecting the inner post
of the second dry battery to any one of the screws at the bottom of
the anemometer case. The lamp used should be a small
flashlight battery lamp for use on two and a half to three
volts. Be sure in making the connections that the ends
of your wire are scraped free from insulation and dirt. This
can be done by cutting off the insulation with the knife and then
rubbing the copper wire bright by a piece of sandpaper or emery
cloth, or even a file. The switch should be left open when you
are not taking readings, in order to prolong the life of your
batteries. By unloosening the little screw in the hub of the
anemometer vanes, you can remove them and also take off the brass
cap on the anemometer case. This should be taken apart once or
twice a month, and some machine used around the bearings to keep
them from wearing out too quickly.
STANDARD ELECTRICAL SUNSHINE RECORDER AND THE GILBERT SUNSHINE
Fig. 39. The standard sunshine recorder is designed for
recording the duration of sunshine electrically, continuously, and
automatically, on a register. The instrument is essentially a
differential air thermometer in the form of a straight glass tube
with cylindrical bulbs at each end, enclosed in a protecting glass
sheath, with suitable platinum wire electrodes fused in at the
center, the whole mounted in a metal socket on an adjustable
The base is secured to the support on the roof so that the glass
tube points north and south, with the blackened bulb toward the
south and lower most, then the tube is inclined at such an angle
that the instrument will begin and cease to record sunshine with the
proper degree of cloudiness. This inclination should be
approximately 45° from the vertical. The machine should be
adjusted at an hour when the sun is wholly obscured.
In temperate and cold climates, slightly different adjustments will
be found necessary at the different seasons of the year.
Fig. 40. The Gilbert Sunshine Recorder consists of a metal
case, cylindrical in form, with a piece of metal turned up on the
ends, dividing the cylinder in half. On each side of the case
are small holes through which the sun casts its rays and records its
movement and duration on a small piece of blueprint paper inside the
cylinder, one piece of the paper being in each compartment.
When the blueprint paper is dipped in
WEATHER BUREAU 53
[Originally contained Figs. 43 & 44]
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water, it becomes entirely bleached, with the exception of the path
made by the sun, which shows up in a blue line.
The sunshine recorder should be set up so that the ends point
directly north and south. The holes pierced in the sides of
the case are nearer one end than the other. The end that the
holes are nearest should be toward the south. It should be
held firmly in place.
The barometer is used for measuring the pressure of the
atmosphere. The principle of this instrument was first
discovered by Torricelli, a pupil of Galileo, the great Italian
philosopher and scientist, in 1643. Many and various types of
instruments have been made, but the two most generally used,
especially where accurate indications are desired, are the mercurial
and aneroid barometers. Either of these instruments are quite
sensitive to changes in the weight or pressure of the earth's
atmosphere, and from their variations we are able to draw
conclusions relative to changes in the weather. Figs No. 41
and 42 illustrate the standard mercurial and aneroid barometers used
most extensively today. A description of these barometer will
serve to make the photographs clearer to the readers of this
MERCURIAL BAROMETER (Fig. 41)
The mercurial barometer in use today is practically the same as that
invented by Torricelli. Of course, many changes have been made
in the case containing the tube of mercury, adding to its
attractiveness, but the principle remains the same.
The standard mercurial barometer consists of a straight glass tube
about thirty-two or thirty-three inches in length, hermetically
sealed at one end. The tube is of half-inch bore and is filled
with chemically pure mercury, which has been boiled in the tube to
insure the total exclusion of all air and moisture. After the
tube has been filled, the opening and is immersed in a cistern of
mercury. Upon immersion the mercury drops in the tube to a
height of 29.92 inches at sea level, or until counterbalanced by the
weight of the surrounding atmosphere pressing up on the surface of
the mercury in the cistern. The space in the top of the tube
is a perfect vacuum and is called the Torricellian vacuum.
The glass mercury tube is enclosed in a brass case. About two
WEATHER BUREAU 55
inchs from the top of the case is an opening extending down the
front and back for a distance of about eight inches. On each
side of this opening is a graduated scale, one side being in inches
and the other graduated in centimeters. The opening is fitted
with a sliding vernier scale graduated in millimeters, thus
permitting the reading of changes in the height of the mercury
column most accurately, as the sliding vernier may be adjusted to
the level of the mercury by means of a thumbs screw fitted on the
side of the case. The cistern containing the mercury is of
glass, with a soft leather or chamois bottom and an adjusting screw,
used to raise or lower the level of the mercury, so that it just
comes in contact with a small ivory point, inserted in the top of
the cistern, and which is used to mark the zero of the scale.
Observations of the changes in the atmospheric pressure should be
taken at regular intervals, and it is necessary to adjust the height
of the mercury in the cistern before each observation. This is
done by bringing the ivory point in contact with the level of the
mercury and then bringing the vernier scale absolutely level with
the top of the column of mercury in the tube, and then take the
The mercurial barometer is a very delicate instrument and when once
placed in the desired position should not be moved. Care
should be taken that the room in which the barometer is
placed is of nearly uniform temperature, for if the temperature
at the top of the barometer is different than the temperature at the
bottom, of course there will be an effect produced on the changes in
the mercury column. All other barometers are set by the
ANEROID BAROMETER (Fig. 42).
The aneroid barometer is so constructed that it contains no liquid
whatsoever, and thus derives its name from the Greek compound word
"aneroid," meaning "without fluid."
The essential parts of the instrument are a metallic case from which
the air has been exhausted, and which contains a spring. The
case of elastic metal is fastened to a base plate at the bottom and
to the spring at the top. The pressure of the atmosphere
causes the case to expand and contract, thus effecting the spring,
which is connected to a needle or dial, causing the dial to move
around on the scale on the face of the instrument and record the
changes. The scale is marked off in inches from 28 to 31, and
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a brass hand or pointer, used to designate the changes in the
atmospheric pressure, there is a small index hand to set over the
needle so that the amount of change in a certain period is easily
known on consulting the instrument.
The dial of the the barometer is marked with the words "Fair,"
"Change," and "Rain," etc., but these words have no significance and
should be disregarded. For instance, 29 1/2 is marked "Change
"; 30, "Fair "; 31, "Very dry"; 28 1/2, "Rain." . If the
barometer, which has been standing at 30.9, suddenly drops down to
29.9, this is positive indication that a storm is approaching, with
strong winds, yet, according to the dial on the aneroid, the reading
would be "Fair." If the barometer were standing at 28
and rose to 29, this would actually indicate approach of cold, dry
weather, and yet on the dial it reads "Rain." This simply goes
to show that the readings on the dial are of no significance
whatsoever, and are not to be relied upon.
The aneroid is not as accurate as an instrument as the mercurial, so
should be checked up occasionally with the mercurial
WEATHER BUREAU 57
The aneroid type of barometer is also used in altitude work, but
must be compensated before using.
This type of barometer possesses several advantages over the
mercurial in that it is portable and therefore used for altitude
work; at sea it is used because there is no fluid to become
unsettled by the motion of the vessel; it is also used in
observatory work because the action is quicker than the mercurial
barometer action and sudden changes likely to occur are
FROM THE BAROMETER
A single observation reading of the barometer is of no
significance. Reading must be taken at different intervals or
the results will be misleading. The important thing about the
barometer is to watch the rise and fall, particularly, whether it is
gradual or rapid. From no single reading can you make an observation
or forecast. A rapid rise indicates that a strong wind is apt
to blow. A rapid fall indicates that the weather will be
unsettled, and that strong winds are apt to blow. Both
indicate a change in the weather, depending upon many things,
particularly however, the direction from which the wind blows.
If an observer stands with the wind blowing on his back, the area of
low low barometric pressure will be at his left, and that of high
barometric pressure at his right. With low pressure in the
west and high pressure in the east, the wind will be from the south;
but with low pressure in the east and high pressure in the west, the
wind will be from the north. The barometer rises for northerly
winds, from northwest by the north to the eastward, for
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WEATHER BUREAU 59
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[Originally contained Figs. 47]
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dry, or less wet weather, for less wind, or for more than one of
these changes - except on a few occasions, when rain, hail, or snow
comes from the northward with strong wind. The barometer falls
for southerly wind, from southeast, by the south, to the westward,
for wet weather, for stronger wind, or for more than one of these
changes, except on a few occasions, when moderate wind with rain or
snow comes from the northward.
A gradual but steady rise indicates settled fair weather.
A gradual but steady fall indicates unsettled or wet weather.
A very slow rise from a low point is usually associated with high
winds and dry weather.
A rapid rise indicates clear weather with high winds.
A very slow fall from a high point is usually connected with wet and
unpleasant weather without much wind.