1820.] the Atomic Theortj. 209 



Dr. Wollaston and Prof. Thomson, for similar reasons, have 

 both adopted oxygen as the most convenient unit ; nor can 

 there be any hesitation in embracing their decision. Oxygen is, 

 in fact, the substance by means of which the weight of the atoms 

 of all other bodies is determined ; hence, the great advantage, 

 for the practical chemist, attending a convenient number for that 

 body. 



Much confusion has arisen in this department of the science, 

 not only from the diversity of the unit, but also from the circum- 

 stance of different chemists having taken the same unit of 

 different values. Eerzelius, as already observed, takes it at 100; 

 Wollaston at 10; and Thomson at 1. There is, indeed, no re;al 

 difference between the three last, for any one of them may be 

 ■converted into the other without an alteration of figures, by 

 simply changing the place of the decimal point. Yet it is much 

 to be desired that the same numbers were steadily employed by 

 all persons, as they would soon be recollected by chemists who 

 would thus have a ready recollection of every compound v/ithout 

 the trouble of referring to a book. 



36. Having observed in my lectures to the students of this 

 college, that the doctrine of atoms was sooner made familiar to 

 the imagination, when the numbers representing their propor- 

 tional weights are reduced to their lowest terms, and being- also 

 more easily remembered when thus expressed, I have preferred 

 the unit adopted by Dr. Thomson. 



37. Gay-Lussac and Thenard, to whom, next to Berzslius, the 

 corpuscular theory of chemistry is most largely indebted, have 

 not failed, with many valuable improvements, to introduce a 

 further perplexity by determining chemical proportions in 

 volumes and not in atoms. Their method is indeed founded on a 

 fact discovered by Gay-Lussac ; namely, that bodies when in a 

 state of gas unite either in equal volumes, or 1 volume of one 

 combines with 2, 3, &c. volumes of the other ; a fact which has 

 been verified by several other distinguished chemists. Berzelius 

 also prefers the computation in volumes ; and though in the 

 meaning of those very eminent chemists volumes are bat another 

 name for atoms, yet it injures the unity and simplicity of the 

 doctrine to represent essential principles in such diversified 

 forms and expressions. It is true that in the present state of 

 our knowledge, the theory of volumes has the advantage of 

 being founded on a well constituted fact, and it admits of our 

 taking a derai-volume in calculation ; while, in the theory of 

 atoms, a demi-atom is an absurdity. But then it is a very 

 forced and unnatural assumption to represent all bodies in a 

 state of gas, even those which were never known to assume that 

 form, or which can be supposed ever to exist in it, in order to 

 determine the proportional weights; of their constituent parts. 

 Hence, as there is in reality no ditierence intended by the theory 

 of volumes, but that of representing bodies in a gaseous, which 



Vol. XVI. >;^ lU. O 



