68 REPORT ON THE STATE CABINET. 



Under the third head, inland distance, I shall also speak of the influence 

 of sea currents upon those places that are situated near the sea coast. 



I, Latitude, or Distance from the Equator. 



Every body knows that the weather is warmer in summer than in 

 winter ; and everybody is also prolaaljly aware that this depends upon 

 the fact that the days are longer than in the winter, no less than upon the 

 fact that the sun "runs higher" as the expression is. But it may not 

 have occurred to all persons that it is perfectly practicable to compute 

 the amomit of heat, and to the average temperature for each part of the 

 earth's sm'face, as it would be if there were no variations caused by 

 the other influences just named. 



I have alluded to the fact that the heat of the sun, or rather its heat- 

 ing power, depends upon its altitude. It varies exactlj^ with what is 

 known to mathematicians as the sine of the sun's altitude. The length 

 of the day is also an element ; for the longer the sun continues to shine 

 on any object the hotter it will become, other things being equal. Rays 

 of heat, also, like rays of light, sufler some refraction as they pass 

 through the air; Isut on the other hand, it has been proved by the 

 experiments of Herschell and Pouillet, that a part of the sun's rays 

 are absorbed by the atmosphere, or rather by the moisture that is con- 

 tained in it, so that only about seventy-five per cent, or three-fourths of 

 all the heat that the sun emits reaches the earth. This absorption 

 of the sun's heat will of course be greater the less the sun's altitude, and 

 consequently will vary with the average of its altitude ; not only for 

 places in different latitudes, hvA also for the same place at different 

 seasons of the j^ear, and for different hours in the day.* 



But in order to express the results thus obtained, in degrees of temper- 

 ature, as indicated by an}^ known standard, it becomes necessary to 



* Of the reality of the fiict referred to, there can, of course, he no douht ; hut I shall take the 

 liberty to doubt the theory or explanation given of it. When heat is absorbed, unless it becomes 

 latent by the mass absorbing it passing from a solid to a fluid, or from a fluid to a gaseous state, 

 the absorbing mass shows the eifect of the heat by an increase in its own temperature. If, there- 

 fore, any portion of the sun's heat were really absorbed by the air, or rather the moisture in it, 

 the temperature of the atmosphere would be raised thereby, and of course the influence of that 

 heat would be felt no less than if it had passed through the air and been returned to it by reflection 

 or conduction from the earth. But if there is anything in the air whereby it can absorb heat, it 

 can, b}' the same means reflect it; so that it shall not reach the earth at all, but be thrown off 

 into space, and thus be totally and entirely lost in its influence upon the temperature of anything 

 within the reach of our observation. And on this theory the amount of heat lost by reflection 

 will depend upon the angle at which it strikes the atmosphere, so that the correction above 

 suggested will answer as well on one theory as the other. 



