34 ON THE HEAT PRODUCED BY FRICTION. 



from the surface was less than half a grain, and the conden- 

 sation inappreciable. 

 Exp 2 Cv'ia- Exp. 2. For the brass cylinder of the preceding experi- 

 ment I substituted one of lead. The two pieces were previ- 

 ously weighed both in air and wateras before. The temper- 

 ature of the air was 9° [48'2 # ], that of the water employed 7° 

 [44*6]. The thermometer, observed every 15 minutes, ex- 

 hibited the following progression in the temperature of the 

 water 10°, 12°, 14°, 1.6° [50°, 53'6°, 57*2*, 60'8°]. The ex- 

 periment continued 75'. Neither the leaden cylinder nor the 

 rubber showed any perceptible diminution of weight or bulk. 

 The point of contact was distinguishable only by a very 

 slight mark on the rubber, and the polish of the surface of 

 the cylinder: whence it appears, that, without any percepti- 

 producedan ble alteration in its bulk or weight, a cylinder of lead, the 

 equal quantity density of which is to that of copper as 11-352 to 8*788, 



produced an equal quantity of heat. 

 Exp. 3. Cylin- Exp. 3. This ^result, the reverse of what the theory of 

 cr of nn. friction seemed to indicate, induced me to make still farther 

 inquiry into the influence of the density of the body rubbed 

 by employing a metal of less density than that of copper; 

 and accordingly I substituted for the preceding a cylinder 

 of tin, the density of which is to that of lead as 7*291 to 

 11 '352. The circumstances being the same, the tempera- 

 ture of the air and water 11° [51*8°], the acquired tempera- 

 ture gave the following progression: 13% 15°, 17°, 18° [55*4°, 

 Produced only 59°, 62*6°, 64,4°]. Hence it follows, that in the same time 

 ^ t 9 u t t hsa3much a cylinder of tin gives but £ of the heat produced by one of 

 copper, while the latter gives an equal quantity to that pro- 

 duced by lead, though its specific gravity is only about 1 8 T 

 of this metal. The volume and weight were found not to be 

 sensibly changed. 

 Exp. 4 Cylin- Exp. 4. A metal, the density of which is still less than 

 ero zinc. ^ t Q f ^ ^ u t ^ e narc ] ness f* which is much greater, and 

 which possesses little malleability, zinc, was substituted for 

 this metal. Rubbed during the same time, with the same 

 velocity, and under the same pressure, the temperature of 

 the air and that of the water employed being 10° [50°], it 

 exhibited the following progression : 12°, 14°, 16°, 18°, 20* 

 Produced more [53-6°, 57*2°, 60'8*, 64*4°, 68°]. The zinc cylinder then, 

 k** 1, less dense than those of copper and lead, afforded a mucb 



larger quantity of heat. Exp* 



