Solar Energy in JRelation to Ice. 139 



marked out, as any map of the world giving Isabnormal 

 lines will at once show. Considerable modifications arise 

 through geographical conditions, such as those connected 

 with the proximity of extensive uplands and plains, and 

 with the relative position in relation to the prevailing winds, 

 or to extensive areas of land or of water. All of these 

 factors are very largely concerned in keeping the centre of 

 oscillation of the temperature at any given spot above or 

 below the theoretical mean for that latitude. There are also 

 many factors which perhaps may be regarded as of minor 

 importance, but which, nevertheless, take a more or less 

 important share in the work of swaying the climatal balance 

 one way or another. These are already well known to even 

 beginners in the study of meteorology; but their connection 

 with other factors which are not so generally recognised, or 

 whose importance in the present connection has been over- 

 looked, is so close that they may well be restated here. 

 Amongst these it has long been know^n that both the specific 

 heat and the latent heat of water and ice play an important 

 part. It requires a much larger quantity of heat to raise a 

 given quantity of water to a certain tem^Derature than it does 

 of any other substance ; and water is also much longer in 

 heating up to a given temperature, or in cooling below it, 

 than any other body. As a consequence of this slow rate of 

 cooling, one could convey a given quantity of warm water to 

 a greater distance before it cooled down to a particular 

 temperature, than one could the same quantity of any other 

 substance warmed to the same extent at the outset. Also, it 

 requires an enormous amount of heat to vapourise water ; 

 and although the facts and figures relating to this are now 

 generally well known, it may serve a useful purpose to repeat 

 them here: — To heat a pound of sea-water 1° F. requires 

 nearly ten times as much heat as would raise 1 lb. of iron 

 1° F. (the specific heat of iron being "lloS). To convert 1 lb. 

 of water into aqueous vapour requires nearly one thousand 

 (965-7) times as much heat as would raise that 1 lb. 1° F. 

 Hence, to convert 1 lb. of sea-water into vapour would require 

 about as much heat as would suffice to raise 5 lbs. of iron 

 2000° F., which is its fusing point. So that, to produce 1 lb. 



