104 



a little higher, mu, with vowels in order. So much for this 

 wonder, if it be the right one ; and it was shown to me as 

 such by one who knew it to be so." 



The following Note " On the Force of aqueous Vapour 

 within the Range of atmospheric Temperature," was read 

 by James Apjohn, M.D., M.R.I. A., Professor of Chemistry 

 in the Royal College of Surgeons. 



Having had it in contemplation some time since to inves- 

 tigate by means of an indirect, but I believe a very accurate 

 process, the caloric of elasticity of the vapours of several 

 liquids, I found myself stopped on the threshold of the in- 

 quiry by a want of knowledge of the tension of such vapours 

 at different temperatures ; for, with the exception of the 

 vapours of water, alcohol, ether, and oil of turpentine, the 

 tension of no others had been made the subject of experi- 

 ment ; and even in the case of the fluids just named, the 

 results recorded in the books appeared to me very far from 

 being of such a nature as to preclude the necessity of further 

 research. 



The method which I intended to employ, in order to ar- 

 rive at the latent heats of vapours, not requiring a knowledge 

 of their tensions beyond the range of atmospheric tempera- 

 ture, it occurred to me, that the necessary data for the solu- 

 tion of the preliminary problem might be obtained with faci- 

 lity, and, at the same time, with much precision, in the 

 following manner : 



Let a known volume of dry air be charged with moisture 

 at any given temperature, and let the expansion produced 

 by the moisture be accurately noted. The pressure being 

 also measured by an accurate barometer, we have the means 

 of calculating the force of the vapour which has produced 

 the expansion. For if v be the volume of the dry air, and 

 v' that of same air when charged with moisture, / the force 



