1 60 Mental value of Scientific Principles. 



latory Theory of Light, largely developed by the 

 labours of Fresnel, renders equally clear and syste- 

 matic an almost endless number and variety of 

 optical phenomena; Oersted's law of Electro-magne- 

 tism similarly explains and renders consistent a 

 multitude of facts respecting the movements of 

 magnets and electric conductors, which would other- 

 wise be confusing to remember and impossible to 

 satisfactorily explain. And the great mental value 

 of these comprehensive ideas to mankind, consists 

 largely in relieving the memory and diminishing 

 mental confusion, by co-ordinating a large number of 

 different facts and apparently inconsistent phenom- 

 ena by means of a general conception which embraces 

 the whole of them. Thus a knowledge of the Prin- 

 ciple of Gravitation informs us that both the ascent 

 of a balloon in the air, and the descent of a stone in 

 water, are alike due to the same force of gravity ; and 

 that of Chemical Affinity proves to us that the ap- 

 parently unlike phenomena of slow rusting of iron and 

 vivid combustion of phosphorus are essentially alike 

 and due to the same cause. 



All bodies, whether living or dead, and all forms 

 of energy, appear to be absolutely subject to the great 

 laws of Causation, Progress, Conservation, &c., no one 

 can escape them ; the man who transgresses the Law 

 of Progress by being too much in advance of his 

 epoch, is punished as certainly as he who lags behind 

 it ; all must advance together, and at approximately 

 the prescribed rates. 



