THEORY DEDUCED FROM PHYSICAL LAWS. 25 



covered the latent heat of steam and the specific caloric of 

 atmospheric air, could hardly be aware that from their dis- 

 coveries would soon arise a theory of meteorology, explain- 

 ing so many atmospheric phenomena. 



The substance of the foregoing pages was written in the 

 autumn of 1833. It will serve to show how I proceeded 

 with my investigations at this early period. 



55. At the time of writing this theory the only point at 

 all doubtful was the specific caloric of air ; I am happy to 

 have it now (January, 1836,) in my power to remove every 

 vestige of doubt on this point, by two new and entirely in- 

 dependent methods. 



First. Professor Apjohn, of the Royal College of Sur- 

 geons, Dublin, has given a formula l for calculating the 

 dew point, assuming as one of the data the specific caloric 

 of air as given by Delaroche and Berard. I have calcu- 

 lated a great number of my own observations, including a 

 range of artificial temperatures of the wet bulb, from 94 

 to 20 Fahr., and I find they give the dew point within the 

 limits of the errors of observation; below that point they 

 begin to deviate rapidly from the true dew point; but this 

 deviation may fairly be attributed to the tables of the elas- 

 ticity of vapor, as given by Dalton and Biot. 



By inverting the formula of Professor Apjohn, as I under- 

 stand it, and calculating the specific caloric of air from rny 

 observations of temperature of air, wet bulb, and dew point, 

 it comes out almost exactly what it is assumed in the essay. 

 I say, as I understand it ; for, as I understand it, I make 

 the specific caloric of hydrogen about fourteen times greater 

 than the professor does, which must arise either from my 

 misunderstanding his formula, or from an inaccurate calcu- 

 lation on his part. We agree in the specific caloric of 

 atmospheric air. 2 



1 Lon. and Edin. Phil. Mag. and Jour, of Science, for Nov. 1835. 



2 It appears since, that Professor Apjohn had neglected to allow for the 

 specific gravity of hydrogen. 



4 



