Jacques Wardlaw Redway

“ Quantitative measurements in temperature, based upon the calorie, have a definite place in physics; and those based on the British thermal unit have a broad application in various economies. Human sensitiveness to heat does not pertain to quantity but to intensity. A large block of ice at 30° may contain more heat, quantitatively considered, than a red-hot horseshoe. If carried into a room whose air was far below freezing, the ice might warm the room to a greater degree than would the horse-shoe. ”

“ Some maximum thermometers set easily; others require to be whirled vigorously. Observers differ in their likes and dislikes. If the column of mercury moves very easily there is always danger of error. If the tube is held in a horizontal position there is the possibility of a slight retreat of the column. And if the bulb is elevated there is always the possibility that it may slide toward the far end of the tube. The maximum thermometer readings are not trustworthy for any except maximum temperatures. When set, it should agree with the reset minimum thermometer. ”

“ The expansion and contraction of the glass with changes of temperature is somewhat greater than with spherical bulbs, but thermometer scales are compensated for this correction.
The bulb of the thermometer is usually filled with mercury at the time it is fused to the stem. While hot, the open end of the stem is inserted in a vessel containing pure mercury. As the air in the bulb cools, its contraction causes a small quantity of mercury to be forced through the bore of the stem into the bulb. ”

“ The daily maxima and minima not infrequently vary several degrees. This is due chiefly to the fact that the less amount of smoke and dust in suburban localities favors absorption of heat in the day time and permits radiation at night.
In early fall and also in late spring, frost may be observed in sheltered places on the ground when the thermometer registers several degrees above freezing. An observer may therefore conclude that his minimum thermometer is not registering correctly. It is not likely than an error has occurred ”

“ An observer who studies the vagaries of his instruments—and they are many—will learn how to master them.
High-air Thermographs.—High-air temperature observations are usually obtained by thermographs secured to kites or balloons. In manned balloons a very sensitive thermograph is contained in a tube through which a current of air is forced. This instrument, the Assmann aspirator, is far more convenient than an ordinary thermograph. Experience has shown that unless the air is in rapid motion, registration is too slow to be trustworthy. ”

“ The front should face the north. The shelter rests on braced legs which should be anchored firmly to the ground. The top of the shelter is likely to become hot enough to radiate heat to the thermometers. This may be prevented in part by a double roof with an air space, or by covering the roof loosely with asbestos cloth or with lino- leum. There can be no objection to placing the shelter in the shade of a tree that shields it from the afternoon sun, provided it is not less than 8 feet from trunk and branches. ”

“ The inaccuracy is always more than 1 degree, and it is likely to vary in different parts of the scale. In many instances these thermometers are sold to jobbers and retailers who stamp fictitious names on them. Experience and practise will usually enable one to discover the maker. The scope of thermometer scales varies greatly. Practically every industry employs temperature measurements which require specially constructed thermometers.
Weather Bureau Thermometers.—Several kinds of thermometers are necessary for the requirements of a weather service ”

“ The prevalence of a stiff wind, especially the northwest wind of cold waves, equalizes temperatures to a remarkable extent; the minima of stations covering considerable areas rarely vary more than 1 or 2 degrees. ”

“ Their object is to hold the index lightly to the place in the bore to which the mercury pushes it. Pushing the indices is the only work the mercury in the U tube performs. Rising temperature pushes the index in the right-hand tube upward; falling temperature pushes the index in the left-hand tube upward. The indices are set by the use of a small magnet which accompanies the thermometer. The poles of the magnet are hollow-ground, so as to fit closely to the tube. ”