390 Dr. Ure's new experimental researches 
will be proportional to the quantity of heat, the repulsive 
power condensed or contained in a given space. Thus if the 
space left for its interposition or lodgment be in one vapour a 
half or a third of the amount of the space in another, we 
ought to find equal tension produced in the former case, by 
a half or a third of the latent heat required for the latter. 
As the principle, I have reason to suppose, is somewhat 
new, let us illustrate it by an application to the three vapours 
in the above list which are most homogeneous, or at any 
rate best understood ; those of alcohol, ether, and water. 
Aqueous vapour of an elastic force balancing the atmos- 
pheric pressure has a specific gravity, compared to air, by the 
accurate experiments of Gay Lussac, of 10 to 16. 
For facility of comparison let us call the steam of water 
unity, or 1.00 ; then the specific gravity of the vapour of pure 
ether is 4.00, while the specific gravity of the vapour of 
absolute alcohol is 2.60. 
But the vapour of ether, whose boiling point is not ioo°, 
but 1 1 2 0 , like the above ether, contains some alcohol ; hence, 
we must accordingly diminish a little the specific gravity of 
its vapour. 
It will then become instead of 4.00 - - 3.55 
Alcohol of 0.823 sp. gr. contains much water; 
specific gravity of its vapour - - 2.30 
That of water as before, unity - - 1.00 
The interstitial spaces in these three vapours will there- 
fore be inversely as these numbers, or 
-7- for ether ; r~ for alcohol; ■— for water. 
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