108 THE ANTARCTIC MANUAL. 
moisture on it the steam is condensing on water, and we know 
exactly what that temperature is: it is and it must be the tem- 
perature of pure boiling water under the existing conditions, and it 
proves nothing as to the temperature at which the steam actually 
quitted the solution. 
The proof that the steam must quit the solution at the tem- 
perature of the boiling solution is furnished by the following 
considerations. We observe that when we blow pure steam into a 
saline solution, it raises its temperature above that of pure boiling 
water, and until a certain maximum temperature is reached, which 
depends on the relation between the salt and the water present. 
As steam continues to pass and to condense in part, owing to the 
lower temperature of the air outside, the temperature of the boiling 
solution falls gradually as the amount of water present increases 
by the condensation of steam. We see then that pure steam of 
independent origin is condensed by a saline solution having a tem- 
perature higher than that of boiling water at the moment, and lower 
than that of its own boiling-point; but it is admitted that the boiling 
saline solution produces pure steam which must be in contact with 
the solution which produces it. If the steam so produced is at the 
temperature at which it would be produced by pure water boiling 
under the same conditions, then it must by contact cool some of the 
solution below its boiling-point. But it has been shown that pure 
steam in contact with a saline solution, the temperature of which 
is ever so little below that of its boiling-point, is condensed by it, 
and has its temperature raised by such condensation. But steam 
of a lower temperature than that of the boiling solution cannot be 
both condensed and generated under the same conditions. We see 
that it is condensed ; therefore it cannot be liberated unless its tem- 
perature is at least as high as that of the boiling solution. There 
is no reason to suppose that it can be any higher; therefore, the 
temperature of the steam leaving a boiling saline solution is the same 
as that of the boiling solution ttself. 
THE DETERMINATION OF THE DENSITY OF SEA WATER BY MEANS OF 
THE ABSOLUTE-WEIGHT HYDROMETER. 
Though the waters of different localities of the ocean differ in 
the amount and nature of the saline matter dissolved in them; it 
has been found that the nature of the dissolved contents can, for 
almost all purposes, be held to be constant; and that, therefore, a 
water is generally characterised by the amount of its dissolved con- 
