172 GREAT MEN OF SCIENCE 



cannon, how hot the casting on the machine became when the 

 borer was blunt. He therefore undertook a series of experi- 

 ments, in order to test the assumptions common at the time 

 concerning the origin of frictional heat. Heavy friction 

 usually results in the production by wear of particles or 

 powder. If the particles had a smaller heat capacity than the 

 original substance, of course to a sufficient degree, the libera- 

 tion of heat in the formation of the particles would be ex- 

 plained. Rumford therefore measured in a mixture calori- 

 meter the capacity for heat of the gunmetal turnings, but 

 found it in no way sensibly different from that of larger pieces 

 of the same metal. It might also be thought that the heat 

 comes from the surrounding air, which has free access. But 

 when borings were undertaken in a closed space, and finally 

 even under water, the development of heat, which was care- 

 fully measured in each case, was in no way diminished. In 

 one experiment, boring was then undertaken under water, 

 with an intentionally blunted borer, for an uninterrupted 

 period of two and a half hours; the water in which the metal 

 was immersed came to boiling point, and continued to boil 

 as long as boring took place. 'It would be difficult to des- 

 cribe the surprise and astonishment of the spectators,' says 

 Rumford, 'when they saw so great a quantity of cold water 

 heated up and finally caused to boil, entirely without fire.' 

 He then calculated the quantity of heat produced in unit 

 time, and found it - not including the obvious loss of heat to 

 the surroundings - at least equal to that given by the com- 

 bustion of nine large wax candles. The borer was kept 

 in motion by two horses, but one only would have been 

 sufficient. This unusual way of obtaining heat by the 

 work of a horse is not however very advantageous, as 

 Rumford remarked; for more heat would be produced by 

 using the horse's food, which cannot be dispensed with, as 

 fuel. 



In conclusion Rumford once more raises the question: 



