SCIENTIFIC HYPOTHESES 203 



energies liberated from the sun, and a great many other apparently 

 diverse phenomena. The " Law " is but the description of the 

 fact that when coal is burnt and has apparently disappeared, 

 it is not really destroyed, but the energy of heat which has been 

 liberated by its oxidation or burning is merely changed into 

 some other form of energy, that of electricity or of motion, or of 

 both. And similarly, the sun's warmth and light which falls 

 upon the growing animal and plant is not lost, but is merely 

 changed into that molecular unrest which constitutes life. 



These two " Laws " will stand as long as the present order 

 of the Universe endures, for they simply describe in generalised 

 language the whole complex and ever-shifting phenomena to 

 which they relate. And while they thus describe in accurate 

 language the phenomena of Nature, they are not inconsistent 

 with — that is, they are not contradicted by — a single fact. And 

 yet, for fifty years or more, this " Law of the Conservation of 

 Energy" has been tested by multitudinous, detailed, and varied 

 experiments conducted in every civilised country throughout 

 that period. And as for the " Law of Gi-ravitation," who is there 

 who doubts that its duration is coincident with that of the 

 Universe itself ? 



And similarly with " Evolution" and " the Survival of the 

 Fittest." They too describe the phenomena of Nature in the 

 domain of li\dng organisms. They are consistent with all that 

 is known of organic life, including Man, and fifty years of hostile 

 criticism has left them strengthened, not weakened, impregnable, 

 not shaken. 



But we should never confound in our thoughts or in our con- 

 versations, the fleeting " hypotheses " which but represent 

 the accomplishing tools, with the permanent "Laws," or, as they 

 are better called, the formulated statement of the "Processes of 

 Nature," which represent the finished product of the accumulated 

 labours of, it may be, many generations of men of science. 



