3*0 APPENDIX. 



inquiry into the source of the Heat that is excited 

 by friction, many interesting experiments are re- 

 lated. From these experiments it appears, that 

 sufficient Heat was produced by the friction of two 

 metallic surfaces (when the access of atmosphe- 

 rical air was entirely prevented) to make water 

 actually boil. It appeared that a very considerable 

 .quantity of Heat was excited by the friction, and 

 given off in a constant stream in all directions^ 

 without interruption or intermission, and without 

 any signs of diminution or exhaustion. 



This ingenious philosopher, when reasoning on 

 these experiments, gives satisfactory reasons to 

 prove that the Heat could not be furnished either 

 by the air, or by the water which surrounded the 

 machinery. And, considering that the source of 

 the Heat generated in these experiments, appeared 

 evidently to be inexhaustible, he naturally con- 

 cluded, that Heal could not be matter: for, says 

 he, " It is hardly necessary to add, that any thing 

 * which any insulated body, or system of bodies, 

 ft can continue to furnish without limitation, can- 

 "-not possibly le a material substance." 



Another method of producing Heat is by the 

 taking place of chemical attractions. Every che- 

 mical attraction, as far as we know, in taking 

 place, produces either Heat or Cold : whether it be 

 simple combination, elective attraction, or com- 

 pound elective attraction. Some of the chemical 

 attractions are attended, besides the production 

 of Heat, with another striking phenomenon, 



namely, 



