386 THE POPULAR SCIENCE MONTHLY. 



of repose, its time of wakefulness and time of sleep ; the other never 

 sleeps till death, but keeps up its incessant action ; the beating of the 

 heart, the introduction of air by breathing, involving millions of 

 movements which never fatigue us, and of which we are indeed, for 

 the most part, unconscious. And, now, who would suppose, that these, 

 the highest and noblest results of a far greater mechanician than man, 

 are ultimately connected with the return of the spring ; and that, in 

 fact, the continuance of the life of man is indissolubly linked with the 

 putting forth of the buds of a tree ? 



Yet so it is ; and surely we cannot spend an hour more profitably 

 than in tracing that connection. Such studies are appropriate to all 

 intelligent men. And, when another sj^ring revisits us, we shall not 

 find that this hour has been entirely lost. The reflections it may sug- 

 gest will, perhaps, increase the pleasure witb which we view the return 

 of that great natural phenomenon. 



In thus explaining to you the connection subsisting between the 

 animal and vegetable kingdoms, I shall have, in the first place, to 

 introduce an account of the great scientific discovery of the last cen- 

 tury — the discovery of oxygen gas — an event rivaling in importance 

 the establishment of the doctrine of universal gravitation by Sir Isaac 

 Newton, in the preceding age. 



Until the middle of the last century an opinion universally pre- 

 vailed that the atmospheric air is a perfectly homogeneous and unde- 

 composable body — that there is but one kind of air, that winch we 

 breathe, and though in mines, wells, and other deep and solitary places, 

 substances somewhat analogous occur, they are in reality nothing 

 more than vitiated forms of atmospheric air, which has gathered poi- 

 sonous qualities from mineral exhalations. From the remotest times 

 these opinions had prevailed. Many of the Greek philosophers looked 

 upon the Olympian Jupiter as only an emblem of the atmosphere, and 

 little suspected that the day would come when that great god of an- 

 tiquity would be anatomized, dissected, and his various parts and 

 qualities displayed. How often do things which have struck one gen- 

 eration with awe become commonplace afiairs in another ! 



It so happened that, though, from time to time, after the thirteenth 

 century, different gaseous substances were accidentally encountered, 

 they all possessed the quality of extinguishing the light of a candle, and 

 were therefore incompetent to support combustion, and when breathed 

 were destructive of animal life. The doctrine that these were only 

 vitiated forms of the atmosphere seemed very plausible, and this in- 

 terpretation was received until the middle of the last century, when 

 the capital discovery was made by Dr. Priestley that the air is not a 

 simple substance, and that there is a great family of analogous bodies, 

 each of the members of which possesses peculiar properties. He com- 

 pletely broke down the ancient doctrine of the elementary nature of 

 the atmosphere. 



