300 Daniell on a new Ih/grometer. 



water and other liquids, at different temperatures," (one of an in- 

 teresting series, read before the.Literary and Philosophical Society 

 of Manchester, and published in thefifth volume of their Memoirs, 

 which it would be difficult to match for originality, and sound 

 philosophical induction,) thus describes his method of finding 

 the force of the aqueous atmosphere : — " I usually take a tall 

 cylindrical glass jar, dry on the outside, and fill it with cold 

 spring- water fresh from the well ; if dew be immediately formed 

 on the outside, I pour the water out ; let it stand awhile to 

 increase in heat, dry the outside of the glass well with a linen 

 cloth, and then pour the water in again : this operation is to be 

 continued till dew ceases to be formed, and then the tempera- 

 ture of the water must be observed. Spring-water is generally 

 about 50°, and will mostly answer the purpose the three hottest 

 months of the year : in other seasons an artificial cold mixture 

 is required." 



However flattered I might have been by any coincidence of 

 opinion with so able a philosopher, the discovery of want of 

 originality damped for a time the ardour of pursuit ; but I have 

 ever since been impressed with the utility of any contrivance, 

 which should enable an observer to mark with precision and 

 expedition the constituent temperature of atmospheric vapour. 

 Upon reading the account of the ingenious contrivance of Dr. 

 Wollaston, which he has termed the Gryophorous, the subject 

 again occurred to me, and I received from that instrument the 

 hint which, after many trials, led to the completion of my 

 hygrometer. 



Plate 5, fig. 1, represents the instrument in its full dimen- 

 sions. A. and b. are two thin glass-balls of 1 ' inch diameter, 

 connected together by a tube, having a bore of about ^th of an 

 inch. The tube is bent at right angles over the two balls, and 

 the arm b. c. contains a small thermometer, d. e., whose bulb, 

 which should be of a lengthened form, descends into the ball b. 

 This ball, having been about two-thirds filled with ether, is 

 heated over a lamp till the fluid boils, and the vapour issues 

 from the capillary tube yi, which terminates the ball a. The 

 vapour having expelled the air from both balls, the capillary 



