132 THE HUMAN MOTOR 



The speed therefore diminishes very little with the stature. 



Now examine the " pressure " exerted by forces (such as 

 the pressure of steam) : they are proportional to the surfaces 

 which are subjected to them, that is to say, to r 2 ; therefore : 



/ = F = r* =f 



s ~ S ~ r 2 



Thus the pressures per unit of area are in the ratio of similitude 

 r. Comparing the muscular forces, without regard to the sections 

 of the muscles, 



f /144\ 3 



J- = r z or I I =0-618, 



and as the weights of the subjects are such that = r 3 , it follows 

 that 



4 = r/r = ' 618 - 

 F M 



the muscular forces are therefore proportional to the weights of 

 the individuals, or to the cube of the ratio of their heights. 



As a matter of fact, the idea of similitude is here a little at 

 fault. This is due very probably to the non-identity of organic 

 materials from one age to another. Newton's law must therefore 

 be applied with extreme cauticn, and, as the writer has always 

 contended, experimental verification should invariably be 

 applied. It was by experiment that Martine in 1720 found the 



relation ^ = r 4 between the muscular forces : the relation of 



forces being equal to the 4th power of the ratio of the 

 heights ( l ) ; this is a relation which conforms better to the results 

 of experiment than that which has been deduced from Newton's 

 formula. 



93. (ii) Alimentation, the Combustible Any motor, to 

 function and produce work, must be fed. It is fed by a stream 

 of energy, and if it is to be always under pressure (as in the case 

 of a steam engine) always ready for work, the stream of energy 

 must be permanent. 



In heat engines the energy expended is of a calorific nature ; 

 it is developed by the combustion of a hydro-carbon (coal, oil, 

 petrol, benzol, alcohol, etc). All combustion is necessarily a 

 producer of exothermic heat ; on an average 1 gramme of oil 

 burning in free air produces 7-50 great calories. 



The combustible is @nly one of the factors of combustion ; the 

 other factor is oxygen, a combustion supporting gas forming 



( x ) Martine De Similibus Animaltbus, Propos, 24 and 25. 



