220 ON THE CONSERVATION OF FORCE 



could not be produced by the aid of the then known mechani- 

 cal forces could be demonstrated in the last century by the 

 aid of the mathematical mechanics which had at that time 

 been developed. But to show also that it is not possible even 

 if heat, chemical forces, electricity, and magnetism were 

 made to co-operate, could not be done without a knowledge 

 of our law in all its generality. The possibility of a per- 

 petual motion was first finally negatived by the law of the 

 conservation of force, and this law might also be expressed 

 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 importance 

 and the scope of our law when you have before your eyes a 

 series of its applications to individual processes in nature. 



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

 moving forces which are at our disposal, directs us to some- 

 thing 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 

 cfxtinct life which has produced the immense coal deposits 

 in the depths of the earth. The forces of man and ani- 

 mals 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. 



