94 TWENTIETH ANNUAL REPORT ON THE STATE CABINET. 



cleg. ; and if in my computation I had corrected for "absorption" 

 or reflection from the atmosphere, the diflference would have been 

 several degrees more. 



So in winter. The coldest day in the general average by obser- 

 vation is February 3d, 19.09 deg ; but the week in which it 

 occurs, the coldest iveek in the year, averages only 23.19 deg. ; 

 whereas hy computation it is 19.08 deg., and if corrected for 

 " absorption," would have been several degrees colder ; but with- 

 out the correction the difference is 4.11 deg., which, added to the 

 summer diflTerence, makes 7.57 deg. 



This diflerence I attribute partly to general influences and 

 partly to local influences that are local and special. Besides all 

 the causes that I have spoken of as influencing climate, there is 

 one more, the eftects of which are not to be overlooked altogether. 

 During the summer a large part of the sun's heat is absorbed by 

 the vegetable growth that is going on. In this Essay thus far I 

 hav^e taken no notice of the theories of heat, but have used terms 

 derived from the old theory of an imponderable, transmissible, 

 measurable substance. I think, however, that that theory has 

 been eflTectually dispersed, and that it has been shown that the 

 word heat is an abstract term, denoting only the condition or pro- 

 perty of bodies. But whatever be the theory we adopt, the result 

 is the same as if heat were a substance which, in the process of 

 vegetable growth, is converted into vital or vegetable force, and 

 thus ceases to appear or to aftect anything for the time-being as 

 sensible heat. Hence for this cause alone, the temperature in the 

 presence of an extensive vegetable growth would not be so hot as 

 if there were no such growth, and the country were a sandy or 

 rocky desert. 



In the winter, however, when the ground is covered with snow, 

 the heat is reflected back at once to a large extent, and does not 

 penetrate the mass ; nor yet, in its immediate influence, does it 

 appear to produce much eflfect upon the temperature of the 

 atmosphere into, or rather through, which it passes. Hence the 

 temperature as indicated by a thermometer will be colder than 

 if there were no snow ; and besides this, the snow is always wast- 

 ling away by evaporation, even in the coldest weather. This pro- 

 |Cess is much accelerated by the direct rays of the sun, and the 

 Imore so, the hotter those rays may happen to be ; consequently a 

 iiarge part of the heat is absorbed, in the process of evaporation, 

 as " heat of liquefaction" for the melting snow. 



