374 AIM AND PROGRESS OF PHYSICAL SCIENCE. 



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 decomposition and combination, the number 

 and diversity of which the chemist with unwearied dili- 

 gence 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 pre- 

 vailing 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 experi- 

 ment that all matter is made up of the elements which 

 have been already isolated. These elements may exhibit 

 great differences as regards combination or mixture, the 

 mode of aggregation or molecular structure that is to 

 say, they may vary the mode of their distribution in 

 space. In their properties, on the other hand, they are 

 altogether unchangeable ; in other words, when referred 

 to the same compound, as regards isolation, and to the 

 same state of aggregation, they invariably exhibit the 

 same properties as before. If, then, all elementary sub- 

 stances are unchangeable in respect to their properties, 

 and only changeable as regards their combination and 

 their states of aggregation that is, in respect to their 

 distribution in space it follows that all changes in the 

 world are changes in the local distribution of elementary 

 matter, and are eventually brought about through Motion, 



