Contents ix 



PAGE 



Demonstration that the Ice produced by freezing Sea- 

 water and similar solutions is pure ice 33 



Analogy between Snow and Sea-ice. The freezing-point 

 of a saline solution is analogous to a Dew-point : Cryohydrates 35 

 De Coppet's experiments on the freezing-points of saturated 



solutions 37 



Experiments in the Engadine in Winter on Cryohydric 



points 40 



Cryohydrates of Salts forming Isomorphous mixtures . 43 

 Land-ice and the mechanics of Glaciers .... 45 

 Importance of the study of the Grain of the Glacier. . 47 

 Sea-ice contains much Brine and flows easily ; Land-ice 

 contains little Brine and flows with difficulty .... 49 



The whiteness of the surface of a Glacier is a secondary 

 feature, due to the disintegration of the Grains by the Solar 



Radiation 50 



Study of boiling mixtures of steam and salts ; analogous 



to freezing mixtures of ice and salts 51 



The boiling-point of a substance is the temperature at 

 which it, as a vapour, condenses on itself as a liquid, and as 

 a liquid, evaporates into itself as a vapour . . . -55 

 Comparison of Barometer and Hypsometer ... 56 

 To determine the boiling-point of a liquid, it should be 



boiled by its own steam 61 



Data relating to boiling mixtures of NaCl, Table VII . 63 

 The thermal law, called Blagden's, is applicable to the 

 boiling-points as well as to the freezing-points of solutions . 66 



The temperature at which steam condenses on a perfectly 

 dry, solid substance is unknown, but when it is moistened in 

 the slightest degree even with dew, the temperature of con- 

 densation is that of water boiling under existing conditions . 67 



Proof that steam produced by a boiling solution must 

 quit it at the temperature of the boiling solution. Meteoro- 

 logical observations and instruments . . . . .68 



The rate of cooling, or its reciprocal, the term of cooling, 

 of a thermometer, is as important a constant as the position 



of the ice-point 69 



The work on this subject by Newton, Lambert and Leslie 

 is classical. 



Term of cooling is an index of thermal nimbleness . . Jo 



The logarithmic law . 75 



Causes of deviation from it ?6 



Effect of silvering the bulb 79 



Difference between a calm in-doors and a calm out-of-doors 80 



b 



