126 MEMOIR OF DR. DALTON, AND 



or break in pieces, the nature of things depending on them 

 would be changed. Water and earth, composed of old worn 

 particles and fragments of particles, would not be of the 

 same nature and texture now with water and earth composed 

 of entire particles in the beginning. And, therefore, that 

 nature may be lasting, the changes of corporeal things are to 

 be placed only in the various separations and new associations 

 and motions of these permanent particles ; compound bodies 

 being apt to break, not in the midst of solid particles, but 

 where those particles are laid together, and only touch in 

 a few points."^ 



This is the perfection of the mechanical theory, unaided 

 by chemistry. It provides for a diversity of particles in 

 size, shape, and other properties, as well as diversity of 

 arrangement, and as this explains what may be called the 

 external phenomena of combination, it is, to a certain stage, 

 probably the correct one. Our difficulties arise when we 

 think on the constitution and mode of combination of these 

 particles. On the first Newton scarcely allows any argument, 

 on the second he has not said sufficient to satisfy the demands 

 of chemistry. 



Dr. Shaw, although not a great discoverer, was a clear- 

 headed man, and his chemical lectures, in 1731, 1732, and 

 1733, are amongst the first in which we see the matter plainly 

 and practically handled, following up the instructions of 

 Boyle, which he carefully edited, f 



At p. 146, he says : — " We must, therefore, observe that 

 the more intelligent of the modern chemists do not understand 

 by principles, those original particles of matter of which all 

 bodies are, by the mathematical and mechanical philosophers, 

 supposed to exist. Those particles remain undiscernible to 



• Newton's Optics, near the end, 

 t Chemical Lectures, publickly read at London in the years 1731 and 1732, 

 and at Scarborough, in 1733, for the Improvement of Arts, Trades, and 

 Natural Philosophy, by Peter Shaw, M.D., F.R.S. Second edition, 1755. 



