196 Dr. Maaieven's Exposition of [Sept. 



astringent power ; the fruit is moulded to the same shape of an 

 acorn, and has the same invariable property of never producing 

 any other tree than an oak. 



All this shows that the elements of bodies are permanent and 

 •unchangeable. Had they been liable to any gradual alteration 

 or waste, the oaks of the present times, composed of those 

 changed materials, would not be found to have the same qualities 

 as the oaks of remote ages ; and the order and course of nature, 

 as well as the qualities of her productions would have been dif- 

 ferent from what they have uniformly appeared, and what we 

 actually find them. 



Such obvious reflections on the course of nature have, in the 

 earliest ages of philosophy, suggested the supposition of a cer- 

 tain number of unchangeable elements, of which it was imagined 

 all things were composed, and on the successive separations and 

 reunions of which depended the decay and reproduction of all 

 iiatural objects. This was the meaning of the opinion ascribed 

 to Democritus, that all things were formed of atoms.* 



We are consequently warranted by the phenomena in assum- 

 ing that the ultimate particles of matter are so perfectly hard 

 and minute as never to wear or divide. It is only by continuing^ 

 entire that the particles may form bodies of the same nature and 

 texture in all ages. Should they wear away, or break in pieces, 

 the nature of all things depending on them would change 

 incessantly, and, contrary to experience and fact, there would be 

 no permanent species of matter. But since the ultimate parti- 

 cles, which henceforth we shall call atoms, are indivisible and 

 indestructible, we may be permitted to deem them also simple. 



2. In the chemical combination of different substances the 

 atoms of those bodies unite together, and this is what causes 

 them to be dispersed through the whole mass. Chalk is com- 

 posed of lime and carbonic acid ; now, how minute a portion 

 soever of chalk we take, we shall find it to contain both lime 

 and carbonic acid. How minute a portion soever of water we 

 take, we shall find it to contain both oxygen and hydrogen. 

 How minute a portion soever of saltpetre we take, we shall find 

 it to contain both nitric acid and potash. Hence, it necessarily 

 follows, that in a chemical compound of the simplest composi- 

 tion every atom of one ingredient is united to one or more atoms 

 of the other. 



3. The extent of this combination is limited. Thus, if a dilute 

 solution of potash be added to an ounce of sulphuric acid, a point 

 is observable, at which the potash and acid lose their peculiar 

 characters, the one of turning vegetable blue colours green, the 

 other of making them red, and a liquid is left of a bitter taste, 

 affording a bitter salt, which crystallizes in short hexangular 

 prisms. If an additional quantity of potash be now added, it 



• Black's Lecture?, vol, ii. p. 4, 



