STATE HORTICULTURAL SOCIETY. 1 97 



of the evergreens offers greater resistance to the motion of the air, so we 

 find they have the higher temperature. 



Several years since, in an essay prepared for the Horticultural Society 

 of my own state, I fully explained the operation of this great law, and, 

 by the application of well known mechanical laws, showed the amount 

 of heat evolved per second by the arrestation of the motion of currents 

 of air having ditt'erent velocities. While engaged on that essay, an 

 intensely cold day occurred favorable for verifying the theory advanced 

 in it, but which had not then, nor, as far as I know, has yet, met with a 

 verification. Not having on my own premises suitable means of verifi- 

 cation, I took a thermometer and went to the well-known botanical gar- 

 den of our munificent citizen, Henry Shaw. 



There is on the west side of his fructicetum a dense hedge of Scotch 

 pine {Pimis sylvesiris)^ planted in triple and quadruple rows. The 

 hedge runs north and south, and is about twenty feet high and about as 

 wide as high. The sky was overcast with a dense, unbroken cloud and 

 the sun had not shone all day. The ground also had for several days 

 been covered with sleet, ice, and snow, several inches in thickness. There 

 was a brisk wind blowing from the west; and the time of day was 

 between two and three o'clock in the afternoon ; so that, if there was any 

 solar influence, it was exerted in favor of the temperature on the west 

 side of the hedge. I found on the west side uniformly a temperature of 

 one degree below zero. Passing to the easb side of the hedge, at some 

 four or five feet from it, I found tliroughout a temperature of four degrees 

 above zero, thus making a diflcrence between the east and west side 

 of the hedge of five degrees. On the northern extremity, the ground 

 rises somewhat abruptly eastwardly. To test the modifying effect of 

 the hedge, I carried the thermometer up eastwardly and found it gradu- 

 ally sinking. At some sixty feet from the hedge I still found it one stand 

 de^riee above zero. I since regret that I did not make observations close 

 to the sides and in the interior of the hedge. I have no doubt it would 

 have shown still greater differences of temperature, since at the nearest 

 distance (four or five feet), where I made the observations, I could feel 

 the rebound of the wind that poured over the hedge. 



The question now arises, what was the cause of the difference in tem- 

 perature between the eastern and western side of the hedge } Unques- 

 tionably it was owing to the arrestation of the motion of the air, its 

 motion being converted into heat. To put this air in motion, some force 

 had been expended, whether heat, light, electricity, or magnetism, it mat- 

 ters not, for the immediate force arising in all cases of an^estation of mo- 

 tion is heat. But, then, heat can not affect matter without starting electric 

 currents, nor can an electric cun-ent exist without magnetism at right 

 angles to it. Again, magnetism develops electricity, and by electric- 

 ity, light, heat, magnetism, and actinism are reproduced. Given any 

 physical force, we can develop any and all the rest by its natural meta- 

 morphosis. Protean like, a physical force is ever changing its form, but 

 never either losing its identity or integrity. This is the great law that 

 unlocks the mysteries of Nature's economy in all her departments, and 



