434 POPULAR LECTURES AND ADDKKSSES. 



dynamics to the position it now holds of a 

 principle pervading all nature and guiding the 

 investigator in every field of science. 



A little article communicated to the Royal 

 Society of Edinburgh a short time before the 

 commencement of the epoch of energy under the 

 title " On the Sources Available to Man for the 

 Production of Mechanical Effect " 1 contained the 

 following : 



" Men can obtain mechanical effect for their 

 " own purposes by working mechanically them- 

 " selves, and directing other animals to work for 

 " them, or by using natural heat, the gravitation 

 " of descending solid masses, the natural motions 

 " of water and air, and the heat, or galvanic 

 " currents, or other mechanical effects produced 

 " by chemical combination, but in no other way 

 " at present known. Hence the stores from 

 " which mechanical effect may be drawn by 

 " man belong to one or other of the following 

 " classes : 



1 Read at the Royal Society of Edinburgh on February 2, 1852 : 

 1'ubli.shed in I'nh ceding of thai date ; and lepublishcd in Vol. I. of 

 Mathematical and Physical Papers. 



