The Wond&r of the World 7 



more nearly resemble in its function an electro- 

 magnetic engine than it resembles a steam-engine, 

 but also that it is a much more efficient engine; 

 that is to say, an animal, for the same amount of 

 potential energy of food or fuel supplied to it call 

 it fuel, to compare it with other engines gives you 

 a larger amount converted into work than any 

 engine which we can construct physically." Lang- 

 ley pointed out that a fire-fly is a much more eco- 

 nomical light-producer than any human lumi- 

 niferous device. As a physicist looking at life and 

 puzzling over its dynamic mystery, Professor Joly 

 advanced the following interesting and important 

 proposition: "While the transfer of energy into 

 any inanimate material system is attended by ef- 

 fects retardative to the transfer and conducive to 

 dissipation, the transfer of energy into any ani- 

 mate material system is attended by effects con- 

 ducive to the transfer and retardative of dissipa- 

 tion." From a dynamic point of view it is 

 wonderful to watch, let us say, a few water-mites 

 imprisoned in a vessel where the supply of food is 

 of the smallest. Day after day, week after week, we 

 see them darting about with extreme rapidity, we 

 hardly ever catch them napping. They cannot 

 evade the law of the conservation of energy, but 

 it certainly seems as if they did. 



Or take another entirely different case the de- 

 structive power of microbes. It seems certain 



