3^6 



making transmutations. (Note A.) It is thus that the foundations 

 >vere 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 morninor twiliofht.''^ 



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 well 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., born 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. 



