314 THE ANIMAL AS A PRIME MOVER. 



temporary suspense of the life of the creature. That this may be 

 done by the employment of pure hydrocarbons indicates that only 

 energy and not material is required, lor no nitrogenous aliment is 

 absorbed or assimilated. 



The measure of these various quantities of energy, useful and wasted, 

 necessary or incidental to the purpose of the existence of a machine 

 or its application to useful work, is, in the case of the external useful work 

 of a laboring man or animal, easily and accurately made; but all the 

 other items are very difficult, and usually, at present, at least, impos- 

 sible of more than approximate measurement, even if any clue can be 

 obtained at all to their methods of action or their absolute and relative 

 quantities. We have not yet discovered the nature of the primary 

 methods of transformation of the energies imported, as latent, into the 

 system, or even what energies are active in the production of the work 

 of the brain and nervous systems and in the automatic operation of 

 the machine. We know enough, however, to prove that the animal 

 machine is a motor of very high efficiency as compared with the prime 

 movers devised by man (his thermodynamic engines, at least), and to 

 indicate, if not to prove, that the machine is a thermo- electric, chemico- 

 dynamic, electro-dynamic, or chemico-electric apparatus, or else a prime 

 mover in which some unknown form of energy, acting by as yet undis- 

 covered methods, is transformed more economically than in any case 

 familiar to the man of science or the engineer of our time. 



The power of animal machines varies greatly with the race and work. 

 Investigations of the quantity of work per pound of the animal ma- 

 chine have been made by the students of aviation, which throw some 

 light upon the problem in hand. 1 Thus Dr. Smith measured the lifting 

 power of a pigeon, as registered by a dynamometer, and computed its 

 expenditure at 160 footpounds per pound of bird, or about 200 pounds 

 weight of bird per horsepower. Alexander computes 270 foot-pounds 

 per pound, 120 pounds weight per horse-power. Penaud finds the fol- 

 lowing, which are thought to be more exact figures : 



Pounds per 

 horsepower. 



Peacock 66 



Pigeon 57 



Sparrow 48 



Seapie , 26 



Were the weight of the pectoral muscles, which actually perform all 

 this work, made the basis of these calculations, these figures would 

 range from 13 to about 5 pounds only per horsepower, thus giving the 

 limiting weight of motor machine. The actual work of rising in the last 

 eases is greater by the amount of slip in the wings, and the bird com- 

 puted to give 60 pounds per horsepower is more nearly 20 pounds, and 

 the last given figure becomes more nearly 5 to 2 pounds than 13 to 5. 

 In full fiight, the demand for power is much reduced, and becomes 



1 Progress in Flying Machines. O. Chanute. Page 39. 



