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fortune to be present at the examination which raised you to the 

 position you now hold in the University, and because I then ventured 

 to predict that you were one for whom a bright future was in store. 

 I now, with pleasure, see you realize a portion of that hope on the 

 present occasion, and most sincerely do I trust that this is only the 

 harbinger of more extensive and brighter triumphs yet to come. 



Professor Jellett read a communication from Joseph Pat- 

 ton, Esq., Professor of Mathematics and Natural Philosophy 

 in Elphinstone College, Bombay, on Hygrometry, and Dal- 

 ton's Theory of Mixed Gases. 



The object of the author in this paper is to controvert the 

 ordinary theory that the particles of different gases have no 

 mutual action. Commencing with the case of aqueous vapour 

 suspended in the atmosphere, he adduces several considerations 

 to show that the known tension of vapour at the surface of the 

 earth could not be accounted for on the supposition that va- 

 pour is only compressed by vapour. 



Thus, for example, the difference between the average 

 elastic force of vapour at Bombay and Mahabaleshwar is equi- 

 valent to '276 inch of mercury. The height of the latter place 

 above Bombay is about 4500 feet, consequently this difference 

 in the elastic force ought to be produced by the vapour con- 

 tained in a column of air 4500 feet high. But even if we sup- 

 pose that through the entire extent of this column the dew- 

 point is 85°, the same as at the base, a supposition which would 

 evidently greatly exaggerate the amount of vapour, Professor 

 Patton shows that the pressure of such a column of vapour 

 would give, for the difference between the tensions at the two 

 places, but '114 inch of mercury, not half the actual diffe- 

 rence. 



Similar conclusions are deduced from the observations of 

 Humboldt, which extend to an altitude of nearly 20,000 feet. 

 From these observations Professor Patton reasons as follows : 

 Taking the dew-point, as observed by Humboldt, at the se- 



