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making transmutations. (Note A.) It is thus that the foundations 
were laid of modern chemistry as an exact science, now so strik- 
ingly contrasting with the dreams of the alchemist, that the effect 
produced on the minds of his contemporaries by the works of 
Lavoisier was (as remarked by my father,* who was then com- 
mencing to occupy himself practically with chemistry) “like 
sunrise after morning twilight.” 
5. The early part of the present century was marked by steady 
increase of knowledge based on the above foundations. Among 
the foremost names in science which its course has witnessed I 
rank John Dalton, who was at once a profound philosopher and 
a man whose personal modesty contrasted strongly with that of 
some would-be “thinkers” of the present day. He investi- 
gated the facts of definite and multiple proportions in the com- 
bination of bodies. He is known as the framer of the Atomic 
Theory, which (differing widely from the mere speculations of 
Lucretius and of those from whom this Roman drew the inspir- 
ation of his noble poem), sought to assign a constant and 
definite weight to the ultimate individual particles of each body, 
and assumed that combination between two kinds of matter 
takes place, not by penetration of their substance, but by jux- 
taposition of their atoms. The definite proportions in which 
bodies combine represent the constant ratio between the weight 
of the juxta-posed atoms. If a given compound be formed by 
the juxtaposition of atoms of different nature, each having a 
definite weight, it is clear that the sum of the weights of these 
atoms must represent the weight of the compound, and the 
smallest conceivable quantity of the compound will be that 
which contains the smallest possible number of elementary 
atoms. This is called a molecule of a compound body, and the 
weight of this molecule will evidently be formed of the sum of 
the weights of all the elementary atoms which it contains. 
6. All this presupposes a certain definite view of the material 
universe, such as is w r ell expressed by Newton. “ All things 
considered, it seems probable that God in the beginning formed 
matter in solid, massy, hard, impenetrable, movable particles, 
of such sizes, figures, and with such other properties, and in 
such proportion to space, as most conduced to the end for which 
He formed them ; and that these primitive particles being solids 
are incomparably harder than any porous bodies compounded 
of them, even so very hard as never to wear or break to pieces, 
no ordinary power being able to divide what God himself made 
* Luke Howard, F.R S., horn in 1772, the year of the deposit of the 
sealed paper (above). Modern chemistry thus seems to me (as it were) only 
two generations old. 
