328 AIM AND PROGRESS OF PHYSICAL SCIENCE. 



Galileo began with the study of terrestrial gravity. Newton 

 extended the application, at first cautiously and hesitatingly, to 

 the moon, then boldly to all the planets. And, in more recent 

 times, we learn that these laws of the common inertia and 

 gravitation of all ponderable masses hold good of the movements 

 of the most distant double stars of which the light has yet 

 reached us. 



During the latter half of the last and the first half of the 

 present century came the great progress of chemistry, which 

 conclusively solved the ancient problem of discovering the ele- 

 mentary substances, a task to which so much metaphysical 

 speculation had been devoted. Reality has always far exceeded 

 even the boldest and wildest speculation, and, in the place of 

 the four primitive metaphysical elements fire, water, air, and 

 earth we have now the sixty-five simple bodies of modern 

 chemistry. Science has shown that these elements are really 

 indestructible, unalterable in their mass, unalterable also in their 

 properties ; in short, that from every condition into which they 

 may have been converted, they can invariably be isolated, and 

 recover those qualities which they previously possessed in the 

 free state. Through all the varied phases of the phenomena of 

 animated and inanimate nature, so far as we are acquainted 

 with them, in all the astonishing results of chemical decompo- 

 sition and combination, the number and diversity of which the 

 chemist with unwearied diligence augments from year to year, 

 the one law of the immutability of matter prevails as a necessity 

 that knows no exception. And chemistry has already pressed 

 on into the depths of immeasurable space, and detected in the 

 most distant suns or nebulae indications of well-known terrestrial 

 elements, so that doubts respecting the prevailing homogeneity 

 of the matter of the universe no longer exist, though certain 

 elements may perhaps be restricted to certain groups of the 

 heavenly bodies. 



From this invariability of the elements follows another and 

 wider consequence. Chemistry shows by actual experiment that 

 all matter is made up of the elements which have been already 

 isolated. These elements may exhibit great differences as regards 



