204 
veral heights, 0, 3281, 6562, 9843, 13,124, and 16,405 feet, 
and assuming, as the most unfavourable supposition, that 
throughout the entire column, between two points of observa- 
tion, the dew-point is the same as at the base, he finds the total 
amount of vapour in a column 19,686 feet high. To this he 
adds one-fourth, as the amount of vapour existing above the 
highest point, and thus obtains the total amount of vapour ex- 
isting in the entire atmospheric column. 
The pressure of such an amount of vapour would only pro- 
duce, at the base of the column, a tension corresponding to a 
dew-point of 47°, the actual dew-point being 81°. Professor 
Patton infers, therefore, that the actual tension of the vapour 
at the surface of the earth cannot depend solely upon} the 
amount of vapour by which it is pressed. ‘The same conclu- 
sion is deduced from the observations of M. Guy Lussac. 
Professor Patton confirms this conclusion by arguments 
drawn from the meteorological phenomena of the tropics. He 
asserts that the hygrometer gives no indication of the mois- 
ture which produces the tremendous tropical rains, amounting 
sometimes to ten inches within twelve hours. 
In further confirmation of his views, as to the mutual ac- 
tion of gases, the author adduces the following argument :— 
If vapour exerts no pressure upon dry air; and if we can by 
any means cut off the lowest stratum of vapour, we should 
thus diminish the total pressure by the weight of the vapour 
existing in the atmospheric column. Acting on this prin- 
ciple, Professor Patton takes a bent glass tube, both ends of 
which are open and turned upwards. Into this tube he pours 
a small quantity of mercury, having previously filled one arm 
nearly to the bottom with powdered chloride of calcium. The 
effect of this substance being to render the air which is in 
contact with it perfectly dry, Professor Patton argues that, ac- 
cording to the ordinary theory, the atmospheric vapour can 
exert no pressure upon the mercury in that side. Hence, the 
mercury in the two arms of the tube ought to show a diffe- 
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