HERMANN VON HELMHOLTZ 



firmed in a striking manner in a great number of 

 instances.' Hence it follows that the total quantity 

 of energy or capacity for work in the universe is 

 constant, and remains eternal and unchanged through- 

 out all the vicissitudes of matter. Energy can change 

 its form and locality without its quantity being 

 changed. The universe possesses a store of energy 

 which is not altered by any change of phenomena, 

 and the quantity can neither be increased nor 

 diminished. Fifteen years afterwards, in 1862, 

 Helmholtz, in a lecture, thus states the principle : 

 c If a certain quantity of mechanical work is lost, we 

 obtain an equivalent quantity of heat or of chemical 

 force, and, conversely, when heat is lost we gain an 

 equivalent quantity of chemical or mechanical force ; 

 and, again, when chemical force disappears, an 

 equivalent of heat or work ; so that, in all these 

 interchanges between various inorganic natural forces, 

 working force may indeed disappear in one form, 

 but then it reappears in exactly equivalent quantity 

 in some other form ; it is thus neither increased nor 

 diminished, but always remains in exactly the same 

 quantity. . . . The same law holds good also for 

 processes in organic nature, so far as the facts have 

 been tested.' J [For the word * force ' it would be 

 better to use the term c energy.'] 



Such a conception of the material world met 

 with much opposition. The older physicists of 



1 Helmholtz's Popular Scientific Lectures, 1873, p. 360. 

 4 2 



