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