METEOROLOGICAL INSTRUMENTS. 



141 



Jones's Hygrometer. (Fig. 

 620.) This instrument is the 

 same in principle as Daniell's 

 hygrometer, but simpler in its 

 construction, more compact, and 

 less expensive. The mercurial 

 thermometer, with its tube at 

 A B, is bent so as to bring its 

 cylindrical ball, C, parallel with, 

 and a little distance from its 

 stem. The bulb is one inch 

 long, and is terminated by a flat- 

 tened surface, D, of black glass, 

 which projects a little beyond 

 the sides of the bulb. The bulb 

 below the flattened surface is 

 covered with black silk. The 

 instrument is supported on the 

 wire, E F, which is attached to 

 the scale by a pivot, that allows 

 the black surface to be inclined 

 to the light. When used, the 

 temperature of the air is first 

 noted ; then ether is poured on 

 the silk cover of the bulb ; and 

 the condensation of the dew is 

 seen on the black extremity of 

 the bulb. Price, $5.00. 



Fig. 620. 



B V* 



Fig. 621. 



Leslie s Thermometric Hygrometer. 

 (Fig. 621.) A thermometric hy- 

 grometer is an instrument formed 

 from a differential thermometer, by 

 covering one of its balls with tissue 

 paper or black silk. Being kept 

 moist with water, the evaporation 

 produces cold, and that in a degree 

 exactly accordant with the state of 

 dryness in the atmosphere. A B, is 

 the differential thermometer ; the 

 ball, B, being naked, that at A, cover- 

 ed ; c, is a vessel of water, which 

 has a few filaments of cotton that reach from the liquor in 



