I 



1821.] Causes of Calorific Capacity, Latent Heat, &,r. 385 



make the recondensation equal to the evaporation, it appeared to 

 me that water ought generally to be of a lower temperature than 

 the atmosphere, or than any other fluid which does not evaporate 

 so fast. To satisfy myself, as 1 did not know of any experiments 

 on the subject, whether this was the case, and how much it may 

 ordinarily be, I made the following experiments.* 



I took* a glass bottle containing between 4 and 5 lbs. avoirdu- 

 pois of mercury, and put it in a cup of spring water, in order to 

 roduce an equal temperature in both. After it had remained 

 ere for some time, half an hour or more, I took four wine 

 glasses, two of one kind and two of another, two thin, and 

 .something of a semi-prolate-spheroidal figure, and two thicker 

 approaching the figure of common beer casks, with about a third 

 of the upper part cut off. These glasses, which I knew were as 

 nearly as it was possible to have them of the same temperature, 

 because they had been together for days in the same place, I 

 put in a row with the two thin glasses on the right hand on a 

 table in the centre of a room without fire, about 13 feet square. 

 The right hand glass, and the next but one, were nearly filled 

 with mercury, and the other two were similarly filled with the 

 water I have mentioned. By this arrangement I had the glasses 

 alternately filled with water and mercury, and one glass of each 

 kind containing the same fluid ; so that I conceived I should 

 thus obviate any discrepancies arising from the sizes, figures, 

 and thicknesses of the glasses, and their position in the room. 

 Between the two middle glasses, on a book, I laid horizontally 

 with its bulb projecting several inches off a delicate thermometer, 

 on the scale of which I could easily read off to the one-sixth, or 

 with care even to the twelfth of a degree of Fahrenheit. After 

 allowing all things to remain in this position some time, 1 

 observed at nine hours, p. m. 



The temperature of the room 68-*-° Fahr. that of the 



Mercury, left hand glass, 68f ; right hand glass, 68^ 

 Water 6?£; 67*- 



This day had been exceedingly warm and dry. Letting all 

 things remain in their present position untd a quarter before six, 

 the next morning, I then found 



The temperature of the room, 66°. 



Mercury left glass, 66 T V ; right glass, 66 T 4 r 

 Water 65 T V; 65^ 



At 8^ hours, a. m. temp, of the room was 65^-°. 



Mercury, left glass, 65 ; right glass, 65 

 Water 64-^ ; 64-J- 



• Since writing this, I find an experiment of this description has been made by Dr. 

 Weils on a more extensive scale : his object, however, was somewhat different to mine. 



New Series, vol. ii. 2 c 



