376 BOARD OF AGRICULTURE. 



us some faint idea of the heat-energy developed by our great 

 central luminary. As a practical question you may ask : 

 "What is the amount of heat which falls with the sunshine 

 upon our farms?" If we take Joule's estimate of the 

 mechanical equivalent of heat, which is probably correct 

 within one per cent., and apply it to the solution of the prob- 

 lem, we obtain an approximative answer. 



At the earth's equator, in the regions watered by the 

 Amazon in South America, the earth receives from the sun 

 sufficient heat upon each square foot every year to raise 

 fifty-three tons to the height of a mile. On our farms in 

 New England, if the heat of our summer months was con- 

 tinued the year round, its aggregate would not fall much 

 below that of the tropical regions. During our cold winters 

 our farms are covered with snow and ice, and the sun's 

 warmth is expended largely in the liquefaction of this cover- 

 ing. We must not forget the paradoxical fact, that now, 

 upon the threshold of our winter, — when the days are 

 shortest, and the cold most severe, — the sun is nearly three 

 million miles nearer to the earth than in July last, when the 

 heat was at its maximum. The obliquity of the sun's rays 

 gives us winter ; not his distance from us. 



The heat that falls upon our farms is disposed of in vari- 

 ous ways ; but it is largely used in maintaining the earth's tem- 

 perature, as vast quantities are radiated into space. Of the 

 immense amount received, it is probable that not more than 

 one-thousandth part of the whole is stored np in our crops 

 and animals, or consumed in labor. This estimate being 

 approximatively correct, how wonderful that this minute 

 fraction is an abundant revenue of power for the whole 

 human race? 



Do we clearly enough comprehend the fact that in the 

 sunlight which is shed upon our farms we find the source of 

 every form of force or energy that comes under observation ? 

 Let us briefly consider this most interesting subject ; and, 

 to render lucid the discussion, I will present a few interrog- 

 atories. What relation does sunlight sustain to the work 

 performed by our oxen and horses, or by ourselves in our 

 daily labor? Work, labor of any kind, is the manifestation 

 of energy, and it depends upon chemical action, upon the 



