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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 
Mumboldt, 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- 
