PROPERTIES AND POWERS. 19 



ocrtain uniformity exists between tlie mechanical force 

 applied, and the amount of heat liberated. It does not 

 appear that we have any proclf of the conversion of 

 motion into physical power. 



It is necessary, to a satisfactory contemplation of the 

 wonderful properties of matter, and of the forces regu- 

 lating the forms of the entire creation, that we should 

 be content with regarding the elementary bodies which 

 chemistry instructs us form our globe, as tangible, pon- 

 derable atoms, having specific and distinguishing pro- 

 perties. That we should, as far as it is possible for 



" "Mr. Joule brought a communication on the same subject before 

 the British Association at Cambridge, which was afterwards 

 published in the Philosophical Magazine, and from that journal 

 the following notices are extracted : 



" The apparatus exhibited before the Association consisted of 

 n brass paddle-wheel, working horizontally in a can of water. 

 Motion could be communicated to this paddle by means of 

 weights, pulleys, &c. The paddle moved with great resistance 

 in the can of water, so that the weights (each of four pounds) 

 descended at the slow rate of about one foot per second. The 

 height of the pulleys from the ground was twelve yards, and 

 consequently when the weights had descended through that dis- 

 tance they 'had to be wound up again in order to renew the 

 motion of the paddle. After this operation had been repeated 

 sixteen times, the increase of the temperature of the water was 

 ascertained by means of a very sensible and accurate thermometer. 

 " A series of nine experiments was performed in the above 

 manner, and nine experiments were made in order to eliminate 

 the cooling or heating effects of the atmosphere. After reducing 

 the result to the capacity for heat of a pound of water, it ap- 

 peared that for each degree of heat evolved by the friction of 

 water, a mechanical power equal to that which can raise a weight 

 of 890 Ibs. to the height of one foot, had been expended. 



" Any of your readers who are so fortunate as to reside amid 

 the romantic scenery of Wales or ScotFand could, I doubt not, 

 confirm my experiments by trying the temperature of the water 

 at the top and at the bottom of a cascade. If my views be cor- 

 rect, a fall of 81 7 feet will of course generate one degree of heat, 

 and the temperature of the river Niagara will be raised about 

 one fifth of a degree by its fall of 1GO feet." Relation between 

 Heat and Mechanical Power: Philosoph. Mag vol. xxyii. 1845. 



