t ON THE SOURCES AND EFFECTS OF HEAT. 633 



serve to be briefly related. He took a cannon, not yet bored, having a pro- 

 jection of two feet beyond its muzzle, a part M-^hich is usMally cast with the 

 piece, in order to insure the solidity of the metal throughout, by the pressure 

 which its weight occasions. This piece was reduced to the form of a cylin- 

 der, joined to the cannon by a smaller neck, and a large hole was bored in it: 

 the whole cannon was then made to revolve on its axis by means of the force 

 of horses, while a blunt steel borer was pressed against the bottom of the hol- 

 low cylinder, by a force equal to about 10 000 pounds avoirdupois; the sur- 

 face of contact of the borer with the bottom of the cylinder being about 2 

 square inches. This apparatus was wrapped up in flannel, when its temperature 

 was about 60°. In half an hour, when the cylinder had made i)()0 turns, the 

 horses being stopped, a mercurial thermometer was introduced into a perfora- 

 tion in the bottom of the cylinder, extending from the side to the axis, and 

 it stood at 130°, which Count Rumford considers as expressing very nearly 

 the mean temperature of the cylinder. The dust or scales, abraded by the 

 borer, weighed only 837 grains, or about -§4^ of the whole weight of ihe cy- 

 linder. In another experiment, the cylinder was surrounded by a tight deal box, 

 fitted with collars of leather, so as to allow it to revolve freely, and the in- 

 terval between the cylinder and the box was filled with 19 pounds of cold 

 water, which was excluded from the bore of the cylinder by oiled leathers 

 fixed on the borer; and after two hours and a half, the water was made to 

 boil. Hence Count Rumford calculates that the heat produced in this man- 

 ner, by the operation of friction, was equal to that of 9 wax candles, each 

 three quarters of an inch in diameter, continuing to burn for the same 

 time. 



A still more rapid increase of temperature may be obtained, where the rela^ 

 tive velocity of the bodies is more cotisiderable, or where they strike each 

 other with violence. Thus a soft nail may be so heated, by three or four 

 blows of a hammer, that we may light a match with it ; and by continuing 

 the operation, it may be made red hot: two pieces of wood may also be set 

 on fire by means of a lathe. When a waggon takes fire, for want of having 

 its wheels properly greased, the friction is probably increased by the tenacity 

 of the hardened tar, which perhaps becomes the more combustible as it 

 dries. 



