V 



63 ANIMAL MECHANISM. 



enormous blocks, called dolmens, which our forefathers 

 erected in prehistoric times, it was admitted that these 

 Titanic works pre- supposed a very advanced knowledge of 

 mechanism. Even now it would require an immense time, 

 or an army of workmen, to execute similar works by employ- 

 ing only the force of man and that of animals. 



We must not imagine that the old Gauls or ancient 

 Egyptians were able to escape from the inevitable necessity of 

 employing many men or an enormous lapse of time in these 

 labours at the period when the only source of mechanical 

 work was that derived from living beings. 



But we live under new and better conditions, thanks to 

 the invention of machinery which develops mechanical work. 

 In addition to the utilization of natural motive powers, such 

 as water courses and wind, man is now able to employ steam 

 engines, by means of which a small quantity of fuel does the 

 work of a great many animals. It is by these means that 

 Egypt has succeeded in a few years in cutting through the 

 Isthmus of Suez, an enterprise which, four thousand years ago, 

 would have absorbed the efforts of many generations. 



Necessity of alternate motion in living motive powers, — When 

 the piston of a machine has reached the end of its stroke, the 

 steam which impelled it must escape, and the piston must 

 return in the opposite direction to accomplish fresh work. 

 In the same manner, the muscle, after having contracted, 

 must be relaxed in order to act afresh. But mechanicians 

 have found that in the alternate movements there is a loss of 

 work. When a heavy object impelled forward with rapidity 

 has to be brought back in the opposite direction, it is neces- 

 sary first to destroy the work which it contains, so to speak, 

 under the form of active force. Precisely in the same manner, 

 when a limb suddenly extended is required to be rapidly bent, 

 the momentum acquired must first be destroyed ; to do which 

 requires an expenditure of work. 



To guard against this loss of motive power, mechanicians 

 have recourse, as much as possible, to the employment of 

 circular movements instead of motion to and fro. Thus, man 

 who is so often inspired in his inventions by the arrange- 

 ments of which nature ofiers him examples, deviates in this 



