METEOROLOGICAL INSTRUMENTS
Monograph Number Two in The Mentor Reading Course
HE history of meteorological instruments dates back at least as far as the fourth century before the Christian era, when the depth of rainfall was measured in India by some form of gauge. We again hear of rain-gauges being used in Palestine in the first century of the present era. Thermometers with fixed scales were used in Italy in the seventeenth century, and the great Galileo, born in Pisa in 1564, took part in perfecting these instruments. Wind-vanes were known to the ancients. The earliest one of which we have any record surmounted the famous Tower of the Winds at Athens. In the Middle Ages the weathercock became the usual adornment of church steeples. The barometer was invented by Torricelli in 1643.
Most meteorological instruments, however, are of quite recent origin, and this is true especially of these types of apparatus that make automatic records, thus replacing, to a large extent, the human observer.
Our picture on the other side of this sheet shows the instruments used by the "co-operative" observers of the Weather Bureau. These observers, of whom there are about 4,500, well distributed over the country, serve the government without pay, and their painstaking observations have alone made possible a detailed survey of our climate. In the picture we see, on the right, an ordinary rain-gauge, and, on the left, a thermometer-screen containing two thermometers; viz., a maximum thermometer, for recording the highest temperature of the day, and a minimum thermometer, for recording the lowest. The screen, which is of wood, painted white, serves to shield the instruments from the rays of the sun, while permitting free ventilation. Under these conditions the thermometers show the temperature of the air; whereas when exposed to direct sunlight a thermometer shows the temperature acquired by the instrument itself, and this may differ materially from the air temperature.
In contrast to this simple equipment, we find at a regular meteorological station, or observatory, an impressive collection of apparatus for observing and recording nearly all the elements of weather. The pressure of the air is measured by the mercurial barometer, and registered continuously by the barograph; the temperature of the air is automatically recorded by the thermograph. Other self-registering instruments maintain continuous records of the force and direction of the wind, the amount and duration of rainfall, the duration of sunshine, the humidity of the air, etc. There are also instruments for measuring evaporation, the height and movement of clouds, the intensity of solar radiation, the elements of atmospheric electricity, and various other phenomena of the atmosphere.
PREPARED BY THE EDITORIAL STAFF OF THE MENTOR ASSOCIATION
ILLUSTRATION FOR THE MENTOR, VOL. 4, No. 10, SERIAL No. 110
COPYRIGHT, 1916, BY THE MENTOR ASSOCIATION, INC.