76 LIFE AND DEATH. 



In the electrical industry we measure by kilozvatts^ 

 which are equivalent to 1.36 horse power, or by a watt, 

 a unit a thousand times smaller. 



Let us add that the power of a machine is not an 

 absolute and permanent characteristic of the machine. 

 It depends on the circumstances under which the 

 work is carried out, and that is why, in particular, we 

 cannot appreciate the power of the human machine in 

 comparison with industrial machines. Experience 

 has shown that the mechanical power of living beings 

 depends upon the nature of the work they are doing. 

 In this connection we may mention some very inter- 

 esting experiments communicated to the Institute, in 

 the year VI., by the celebrated physicist, Coulomb. A 

 man of the average weight of 70 kilogrammes was 

 made to climb the stairs of a house 20 metres high. 

 He ascended at the rate of 14 metres a minute, and 

 he performed this daily task for four effective hours. 

 This work was equivalent to 235,000 kilogrammetres. 

 But if, instead of climbing without a burden, the same 

 man had had to carry a load, the result would have 

 been quite different. Coulomb's workman took up 

 six loads of wood a day to a height of 12 metres 

 in ^6 journeys, corresponding to a maximum 

 work of 109,000 instead of 235,000 kilogrammetres. 

 The mechanical power of the human machine 

 thus varied in the two cases in the ratio of 235 

 to 109. 



The Two Aspects of Mechanical Energy: Kinetic 

 and Potential, — Energy, or mechanical work, may 

 present itself in two forms — kinetic energy, corre- 

 sponding to the mechanical phenomenon which has 

 really taken place, and potential energy, or the energy 

 of reserve. 



