PROGRESS OF HUMAN KNOWLEDGE. 15 



the theory of an acidifying principle derived from 

 the discoveries of Lavoisier, are other examples in 

 point, as is also the Emission theory of Light, long 

 implicitly held and successfully applied to the solu- 

 tion of many phenomena. I would cite the Primitive 

 Cell theory of our own time as another instance. 

 Physiologists exulted in the discovery of this common 

 germ of all vital organisation, as though it were a ter- 

 minus in this line of research, not duly considering 

 that cells themselves are a product of organisation, and 

 tli at they contain matter which has better claim than 

 its receptacle to be regarded as germinal to the won- 

 derful varieties of life issuing therefrom. Without 

 noting other such instances, we may set them down 

 generally as mere pauses in the march of science 

 often, indeed, as convenient resting-places whence to 

 obtain more distinct views of the objects to be sought 

 for beyond. 



The vast accession of knowledge to man from study 

 of the elements of Matter and Force in the universe 

 necessarily implies some change in the amount, as well 

 as methods of use, of his intellectual powers. I have 

 already spoken of the more perfect understanding of 

 what is Truth as founded upon evidence. Inventive- 

 ness is another faculty of mind awakened and enlarged 

 by the researches of experimental science, as well as 

 by that spirit of competition which civilised life en- 

 genders and sharpens. The mind grows within itself 

 by exercise of its powers ; and we have some reason 

 for supposing that this growth may become hereditary ; 



