376 FARADAY 



atmosphere to which we have given it in the form of car- 

 bonic acid, and they are growing and prospering. Give 

 them a pure air like ours, and they could not live in it ; give 

 them carbon with other matters, and they live and rejoice. 

 This piece of wood gets all its carbon, as the trees and plants 

 get theirs, from the atmosphere, which, as we have seen, 

 carries away what is bad for us and at the same time good 

 for them what is disease to the one being health to the 

 other. So are we made dependent not merely upon our fel- 

 low-creatures, but upon our fellow-existers, all Nature be- 

 ing tied together by the laws that make one part conduce 

 to the good of another. 



There is another little point which I must mention before 

 we draw to a close a point which concerns the whole of 

 these operations, and most curious and beautiful it is to see 

 it clustering upon and associated with the bodies that con- 

 cern us oxygen, hydrogen, a,nd carbon, in different states 

 of their existence. I showed you just now some powdered 

 lead, which I set burning ; ( u ) and you saw that the mo- 

 ment the fuel was brought to the air it acted, even before 

 it got out of the bottle the moment the air crept in it 

 acted. Now there is a case of chemical affinity by which 

 all our operations proceed. When we breathe, the same 

 operation is going on within us. When we burn a candle, 

 the attraction of the different parts one to the other is go- 

 ing on. Here it is going on in this case of the lead, and 

 it is a beautiful instance of chemical affinity. If the prod- 

 ucts of combustion rose off from the surface, the lead would 

 take fire, and go on burning to the end; but you remember 

 that we have this difference between charcoal and lead 

 that, while the lead can start into action at once if there be 

 access of air to it, the carbon will remain days, weeks, 

 months, or years. The manuscripts of Herculaneum were 

 written with carbonaceous ink, and there they have been for 

 1800 years or more, not having been at all changed by the 

 atmosphere, though coming in contact with it under various 



18 Lead pyrophorus is made by heating dry tartrate of lead in a glass tube 

 (closed at one end, and drawn out to a fine point at the other) until no more 

 vapors are evolved. The open end of the tube is then to be sealed before 

 the blowpipe. When the tube is broken and the contents shaken out into the 

 air, they burn with a red flash. 



