246 PRINCIPLES OF THE MECHANICAL THEOEY OF HEAT. 



friction matcb derives its great utility from the lieat supplied by a slight rubbing 

 of the kindling matter. 



The first scientific experiments on the development of heat by friction were 

 those which Count Rumford instituted in the cannon foundry of Munich, (G-il- 

 herfs annal. xii, p. 554.) In order that the muzzle of -the cannon, which in 

 founding is uppermost, may not become porous, a massive cylindrical piece of 

 metal is cast thereon, usually called "the rejected head," {der verlorene Kopf.) 

 In one experiment Count Rumford inclosed the rejected head of*a six-pounder 

 in an oblong wooden box, open at the top and filled with water. Through one 

 end of this box was passed, water-tight, the narrow neck which united the head 

 to the cannon ; and through the other, also water-tight, the stem of a steel borer. 

 The cylindrical head was 9.8 inches long and 7.75 inches in diameter. The box 

 was charged with 18| pounds of water ; the arrangement being horizontal, the 

 cannon and the attached head were made to revolve by horse-power at the rate 

 of 32 revolutions per minute, the borer, at the same time, being pressed against 

 the end of the head. The temperature of the water was raised after one hour 

 41° C; after one and a half horn-, 61° C. ; after two hours, 81° C. To 

 the wonder of the spectators the water, at the expiration of two and a half 

 hours, was actually boiling. The cylinder and the spindle of the borer were 

 also heated to the same temperature. During the two and a half hours 4,145 

 grains (about 17 half-ounces) of metal shavings had been turned out. 



The experiment not being easily repeated in the form above given, a very 

 elegant and commodious apparatus for exhibiting the same result has been 

 devised by Professor Tyndall. On the axis of rotation of a small wheel (driven 

 by a large one) is screwed a glass tube a, (Fig. 2,) open above and closed below, 

 and having a length of about 12 centimetres, with a diameter of rather more than 

 two centimetres. This tube is not quite filled with water, and is held firmly 



Fig. 2. 



between tv/o boards of hard wood, provided with semi-circular grooves, the boards 

 being connected by a hinge on one side, and on the other pressed against the tube 

 with the hand. If the fly-wheel be now thrown into rapid rotation, so strong a 

 friction is exerted upon the circumference of the tube that the temperature of the 

 water is quickly raised, as may be easily shown by a thermometer, and finally 

 attains the boiling point. If the tube be made air-tight, with a cork not too 

 firmly fixed, the latter will be thrown out through the elasticity of the enclosed 



