The thermometer is the instrument that measures temperature. It was not until eighty-seven years after Columbus discovered America that Galileo discovered the principle of the thermometer. This first instrument was crude. It consisted of a glass bulb, containing air, terminating below in a long glass tube, which dipped into a vessel containing colored water. When the temperature fell the contraction of the air in the bulb caused the water to rise in the tube, and when the temperature rose the expansion of the air forced the water to a lower level. Galileo also invented the alcohol thermometer in 1611, but the determination of the zero and some fixed point above it, by which to graduate the scale, took years to evolve. The modern alcohol and mercury thermometers consist of a bulb filled with the liquid, and a tube partly filled, the upper part being a tolerably complete vacuum, allowing the liquid freedom of movement up and down the tube. When a tube is broken one is surprised to see that the diameter of the bore is less than that of the smallest fuzzy hair from the back of the hand. The size of the column of mercury is magnified by the action of light passing through the glass of the tube.
Temperatures are usually taken in the shade. The instrument should be free from all bodies that could conduct heat to it, and it should have free circulation of air about it.
In a complete meteorological station automatically recording instruments, too complicated for the use of the layman, record for each moment of time the temperature of the air and its pressure, the periods of sunshine, the duration and the amount of rainfall, and the direction and velocity of the wind.
CHAPTER VI
THE ADVANTAGE OF TAKING WEATHER
OBSERVATIONS AND APPLYING THEM TO
ONE’S PERSONAL NEEDS
FORECASTS MADE FROM THE ANEROID BAROMETER—COLDS PREVENTED BY MOISTENING AIR IN LIVING ROOMS—A CRIMINAL HANGED AND AN INNOCENT MAN FREED BY WEATHER RECORDS
Observations from Kites. It is strange that the Chinese, who have been flying kites many thousand years, should not have made improvements in the primitive construction of these devices. It remained for Wendham, in 1866, to perceive the advantage of superimposing two or more planes, one above the other, for the purpose of securing a larger area of sustaining surface. After examining [Figure 3] almost any one can build an efficient kite. Heights of two to three thousand feet may be reached by using cable-laid twine No. 24, but in order to gain great altitudes pianoforte wire must be used. Soft pine is the best and most available material. Spruce is stronger, but more difficult to secure. The sticks should be straight-grained. The cloth may be silk or the stronger and finer grades of cotton. It should be torn, not cut. The ends will then be true and square with the fiber of the cloth. Kites are used not only to secure weather observations, but they have been used to draw sleds in the Arctic region, and to draw wagons and boats. By adjusting the points at which the pulling cords are attached to the boat an ingenious sailor is able to proceed nearly at right angles to the direction of the wind.
Fig. 3.—Standard Weather Bureau Kite.
When it is known that a box kite having only sixty square feet of sustaining surface, flying at a considerable height, may lift a person of ordinary size, one is impressed with the idea that vessels of commerce might employ kites of large dimensions to increase the speed of sailing ships. The kites would fly in a stratum whose velocity is not restricted by friction with the surface of the water.