air thermometer

An instrument which is designed to measure the degrees of heat by means of the expansion of air. When used to measure small differences of temperature, it is a capillary tube with a bulb at the upper end, and with its lower end plunged into a coloured liquid in a bottle. The air in the bulb at the top is heated, so as to cause a portion of it to be expelled, leaving the coloured liquid free to rise a certain distance in the tube. An alteration of temperature will then make the remainder of the air in the tube to expand or contract with the effect of making the liquid correspondingly fall or rise in the tube. Within certain limits it is a delicate thermometer, and was the first form of that instrument as invented in 1590, by San to rio, a physician of Padua. It can measure only the lower temperatures. When employed to note higher degrees of heat, a bent capillary tube is substituted for the straight one. It agrees with the mercurial thermometer up to 260°, but above that point mercury expands relatively more than air. The differential thermometer of Sir John Leslie is a modification of the air-thermometer. [DIFFERENTIAL THERMOMETER ] Kinnersley's Electric Air-thermometer: An instrument consisting of a gla tube closed at both ends by air-tight bra caps, through which two wires slide in the direction of the axis of the tube. These wires are terminated by bra balls, which are made to approach within the striking distance. To an aperture in the bottom of the lower cap is fitted a bent tube of gla , which turns upwards, and is open at both ends; the bend is filled with mercury, or with a coloured fluid, which may indicate by its rising or falling within the tube any dilatation or contraction that may take place in the air within the ve el. Every time a spark pa es between the bra balls the fluid suddenly rises, but descends again to its old level immediately after the explosion. air-threads, or air-go amers, s . The name given to the long slender filaments often seen in autumn floating in the air. They have been darted out by spiders, especially the Aranea obtextrix , which, mounting to the summit of a bush or tree, darts such threads out till it succeeds in launching one strong enough to support it, and float it up into the air, which it desires to ascend in quest of prey.