740 



to give/ = the elasticity in inches of mercury for temp. Fahr,, he 

 gives a table of / for every degree from —40° to +360^, by the help 

 of which he compares with his formula, the experiments of Robison, 

 Southern, Dalton, Taylor, Arsberger, Ure, and those of the American 

 Committee, and shows that they differ more widely from each other 

 than from the formula. 



Considering the care bestowed to ensure the elasticities being cor- 

 rectly measured, the author is disposed to attribute a great part, but 

 not the whole, of the discordance on the several results to errors in 

 the measures of temperature arising from smallness of scale or incor- 

 rectness of division. 



February 24, 1848. 

 GEORGE RENNIE, Esq., Treasurer, in the Chair, 



" On the Moist-Bulb Problem." By Captain Shortrede. Com- 

 municated by Lieut.-Colonel W. H. Sykes, F.R.S. 



The author adopts the notation of Professor Apjohn, and by a 

 similar method deduces the fundamental equation, which is then 

 translated into numbers, taking 1175° F. as the sum of the latent 

 and sensible heats, 0*267 as the specific heat of dry air, the weight 

 of aqueous vapour as five-eighths of that of air, and its specific heat 

 = 0'867, that of water being unity. 



The coefificient for barometric pressure is resolved into a simple 

 change on the temperature of the air, and consequently also on the 

 depression of the moist bulb ; and the equation is put into a shape 

 convenient for use, and shown to be free from objection. The 

 author uses the table of the force of vapour, given in the accom- 

 panying preceding paper, and then gives a table of maximum 

 depressions for every degree of the moist bulb from —40° to 212°, 

 and another table interpolated from it for every degree of temperature 

 of the air from 0° to 212°. 



Gay-Lussac's depressions are then compared with those of the new 

 formula ; and the errors are shown to be almost insensible near the 

 freezing-point, but increasing gradually, till at 25 Cent, it is about 

 10 per cent. The author attributes these errors to the gradual de- 

 terioration of the chloride of lime during the experiments. 



The author then compares Prinsep's maximum depressions collected 

 and given in vol. v. of the Journal of the Asiatic Society of Bengal. 

 The observed depressions are generally below those given by the new 

 formula, like those of Gay-Lussac. The errors on those where the 

 air was heated by a steam-pipe, are not greater than on those at na- 

 tural temperatures ; and that with air passing through a porcelain 

 tube at an orange heat, falls within the limits assigned by Prinsep in 

 estimating the temperature of the air. 



Apjohn's maximum depressions are then compared with the new 

 formula. And here the errors are of an opposite character to those 

 preceding, which the author attributes to the lowering of tempera- 



