302 ox THE COXSERTATIOJf OF FOKCE. 



pressed in the practical form that no perpetual motion is 

 possible, that force cannot be produced from nothing ; 

 something must be consumed. 



You will only be ultimately able to estimate the im- 

 portance and the scope of our law when you have before 

 your eyes a series of its applications to individual processes 

 on nature. 



What I have to-day mentioned as to the origin of the 

 moving forces which are at our disposal, directs us to 

 something beyond the narrow confines of our laboratories 

 and our manufactories, to the great operations at work in 

 the life of the earth and of the universe. The force of 

 falling water can only flow down from the hills when rain 

 and snow bring it to them. To furnish these, we must 

 have aqueous vapour in the atmosphere, which can only 

 be effected by the aid of heat, and this heat comes from 

 the sun. The steam-engine needs the fuel which the 

 vegetable life yields, whether it be the still active life of 

 the surrounding vegetation, or the extinct life which has 

 produced the immense coal deposits in the depths of the 

 earth. The forces of man and animals must be restored 

 by nourishment ; all nourishment comes ultimately from 

 the vegetable kingdom, and leads us back to the same 

 source. 



You see then that when we inquire into the origin of 

 the moving forces which we take into our service, we are 

 thrown back upon the meteorological processes in the 

 earth's atmosphere, on the life of plants in general, and 

 on the sun. 



