228 DICTIONARY OF AVIATION
thermometer having the bulb and a portion of the stem coverd with lampblack, the whole being placed in a glass vacuum-tube to prevent less of heat by convection. It is often used along with a bright-bulb thermometer similarly encased.
Celsius thermometer, a thermometer introduced by Cel- sius in 1736, in which the zero is at the boiling-point of water, and the loo-degree-mark at the melting-point of ice. This thermometer, by whose use plus and minus degrees in ordinary atmosferic temperatures ore avoided, has never been extensivly used.
centigrade thermometer, a thermometer introduced by Linnaeus, in which the zero is at the freezing-point of water and the loo-degree-mark at the boiling-point of water. This thermometer is in common use in many coun- tries of the continent of Europe, and is there and elsewhere extensivly employd in scientific work.
Fahrenheit thermometer, a thermometer devised by Fah- renheit, in which the zero is at 32 degrees below the melt- ing-point of ice, and the 2i2-degree-mark at the boiling- point of water. This thermometer is in common use in English-speaking countries and in Holland
maximum thermometer, a thermometer which registers the maximum temperature to which it is exposed, as those of Rutherford, Phillips, and Negretti.
minimum thermometer, a thermometer which registers the minimum temperature to which it is exposed, as the alco- hol minimum thermometer devised by Rutherford in 1704. Reaumur's thermometer, a thermometer in which the zero is at the freezing-point of water and the 8o-degree-mark at the boiling-point of water. This thermometer was formerly extensivly used in Germany and Russia.
thermoscope 'Oerz-m^skop n. an instrument for indicating minute variations in temperature without mesuring their amount.
thread-feather '0sed,fed3z n. one of the thred-like or hair- like fethers usually closely associated with the contour- f ethers of birds; a filoplume.
throttle 'Gsetl n. a valv, as in the eduction-pipe of a steam- engin, for controlling the flow of steam; a threttle-valv.
thrust OsAst n. a posh or shove; also, the horizontal compo- nent of a positiv pressure of the air, as upon an aeroplane or other aerofoil; positiv drift.
thunder 'GAndsz n. the loud noise which follows a flash of lightning, due to the same discharge of electricity in the air to which the lightning is due, but occurring a little later
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