54 ON SOME ASPECTS OF THE 



Case himself stated that Newton passed from terrestial 

 to celestial mechanics. In the language of Tyndall, this 

 ' passage from a falling apple to a falling moon ' was a 

 stupendous leap of the imagination, for his enunciated 

 law applies in conception to the universe, thus extending 

 into boundless space and persisting through endless time. 



The hypothesis of the luminiferous ether is, without 

 doubt, a conception of the imagination. It was first sug- 

 gested by Hooke in 1682, but was set forth in its present 

 form by the Dutch physicist, Huyghens, in 1690. It 

 postulates the existence of an all-pervading medium, 

 having properties unlike those of gross matter ; boundless 

 in extent, it has no weight, and is in this sense immaterial, 

 hence it offers no resistance to the passage through it of 

 material bodies. It is further conceived as the seat of 

 disturbances, which are propagated as etherial undula- 

 tions or waves in all directions with enormous velocities 

 and under varied complexities of form. Although 

 absolutely a creature of the imagination, the hypothesis 

 has acquired scientific validity through the circumstance 

 that it renders the complex phenomena of light, heat and 

 electricity susceptible of causative explanation, whilst a 

 further guarantee of its possessing a rational basis is 

 afforded by the innumerable instances of its employment 

 having resulted in verified predictions. 



The theory of the conservation of energy was first 

 propounded by Mayer in 1842, and established on its 

 present wide basis by Joule. It is a conception fraught 

 with results of immense practical utility, whilst it has 

 produced momentous changes in human thought. 

 ' Broadly enunciated, the principle of the conservation 

 of energy asserts that the quantity of what we term 

 force in the universe is as unalterable as the quantity of 

 matter ; that it is alike impossible to create force or to 



