324 



ATOMIC THEORY ATOOI. 



of hanl, ponderable, impenetrable, inactive, and im- 

 nmiuMc particles, from the variety in the composi- 

 tion of which, the variety of bodies originates. A 

 system founded on the theory of atoms is called 

 atomic, e. g., that of le Sage ; sometimes it is also 

 called corpuscular philosophy, and is opposed to the 

 ilynamic theory. (See this article.) In Germany, 

 the tl i eory of atoms finds very few adherents: it is 

 generally thought, in that country, a gross concep- 

 tion of the universe, and a very unsatisfactory one. ;is 

 it only removes the question respecting the nature of 

 matter one step farther. In France and Britain, the 

 number of believers in it is greater. 



ATOMIC THEORY, in chemistry. Two opposite opi- 

 nions have long existed concerning the ultimate 

 elements of matter. It is supposed, according to one 

 party, that every particle of matter, however small, 

 may be divided into smaller portions, provided our 

 instruments and organs were adapted to the opera- 

 lion. Their opponents contend, on the other hand, 

 that matter is composed of certain atoms, which are 

 of such a nature as not to admit of further division. 

 These opposite opinions have, from time to time, been 

 keenly contested, and with variable success, accord- 

 ing to the acuteness or ingenuity of their respective 

 champions. But it was at last perceived that no 

 positive data existed capable of deciding the question ; 

 and its interest, therefore, gradually declined. The 

 progress of modern chemistry has revived the gene- 

 ral attention to this controversy, by affording a far 

 stronger argument in favour of the atomic constitu- 

 tion of bodies than was ever advanced before, and 

 which seems almost irresistible. We have only, in 

 fact, to assume, with Mr Dalton, that all bodies are 

 composed of ultimate atoms, the weight of which is 

 different in different kinds of matter, and we explain 

 at once various laws of chemical union. According 

 to this view, every compound is formed by a combi- 

 nation of the atoms of its constituents. An atom of 

 A. may combine with 1 , 2, 3, or more atoms of B 

 an arrangement on which depends the law of multi- 

 ples. If water, for example, is composed of an atom 

 of hydrogen and an atom of oxygen, it follows that 

 every compound of hydrogen with au additional quan- 

 tity of oxygen, must contain 2, 3, or more atoms of 

 oxygen ; some multiple, in a word, by a whole number 

 of the quantity of oxygen contained in water. It is 

 equally clear, from this view of the composition of 

 water, that the weight of an atom of oxygen is eight 

 times heavier than an atom of hydrogen. The rela- 

 tive weight of the atoms of other substances may be 

 determined in a similar manner. Thus an atom of 

 carbon is six times, an atom of sulphur sixteen times, 

 and an atom of chlorine thirty-six times, heavier than 

 an atom of hydrogen ; and this explains why they 

 unite with one another in the proportions expressed 

 by those numbers. What are called the proportional 

 numbers are, in fact, nothing else but the relative 

 weights of atoms. No one can suppose that the laws 

 of chemical union are the effect of cliance : there 

 must be some cause for them in the nature of the 

 ultimate particles of matter. This cause, as we have 

 just seen, is completely supplied by the supposed 

 atomic constitution of bodies, which accounts for the 

 phenomena in the most beautiful and consistent man- 

 ner. So perfect, indeed, is the explanation, that the 

 existence of these laws might have been predicted 

 by the aid of the atomic hypothesis long before they 

 were actually discovered by analysis. But these are 

 not the only arguments which we at present possess 

 in favour of the existence of ultimate indivisible par- 

 ticles Of matter. Doctor Wollaston, in his paper on 

 the Finite Extent of the Atmosphere (Philosophical 

 Transactions, 1822), has defended this side of the 

 question on a new and independent principle ; and 



the proof he has jjivi'n of the atomic constitution of 

 lux lies appears decisive. Some chemists, even with- 

 out expressly adopting the atomic theory itself, lia\e 

 followed Mr Dalton in the use of the terms atom and 

 atomic wight, in preference to proportion, coiiilii/iiiii; 

 proportion, ri/uiriilrnt, and others of a like kind. All 

 these appellations, however, have the same significa- 

 tion ; and, in using the \vonl atom, instead of the 

 others, it should he held in mind that it merely de- 

 notes the proportions in which bodies unite; that it 

 is the expression of a fact which will remain the 

 same, whether the atomic hypothesis which suggested 

 the employment of the term IK- true or false. Then- 

 is one circumstance which, at first view, seems hos- 

 tile, to the supposed atomic constitution of matter. 

 According to the law of multiples (see Chemical 

 I'.i/iiiruli-ntii), oxygen in the three oxides of lead is in 

 the ratio of 1 : 1 : 2 ; so that, if we regard the pro- 

 toxide as composed of one combining proportion of 

 lead to one proportion of oxygen, the second will 

 contain one proportion and a half, or, according to 

 the atomic theory, one atom and a half of oxygen. 

 Now, though the half of a combining proportion may 

 be admitted, the existence of half an indivisible par- 

 ticle of matter is inconceivable; and this circum- 

 stance would be fatal to the atomic theory, were there 

 not some satisfactory mode of accounting for it. Se- 

 veral explanations might be brought forward. One 

 of them, which has found its advocates, rests on the 

 supposition that what is called the protoxide, is, in 

 reality, composed of one atom of lead to two atoms 

 of oxygen ; and that the real protoxide lias not yet 

 been discovered. Another mode of accounting for 

 the anomaly is, by regarding the present deutoxide 

 as composed of the protoxide and peroxide combined 

 with each other. A third method is, by doubling 

 both elements of the anomalous compound, by which 

 the exact ratio is preserved, and the idea of the frac- 

 tion of an atom is avoided. Thus the protoxide and 

 peroxide of iron are composed, the first, of one pro- 

 portion, or 28 of metal + 8 of oxygen, and the se- 

 cond, of 28 of metal + an atom ana a half, or 12 of 

 oxygen ; or, what amounts to the same thing, of 56, 

 or two atoms of iron, to 24, or three atoms of oxygen. 

 These observations prove, that the occurrence of half 

 proportions is not inconsistent with the atomic con- 

 stitution of bodies : they show that the difficulty is 

 explicable, and probably will, in the progress of dis- 

 covery, be entirely removed. In the meantime, 

 however, it would be inconvenient to allow any spe- 

 culative notions on the subject to interfere with actual 

 practice; and, therefore, it is best at once to admit 

 the occurrence of half proportions ; and, if any one 

 'prefer the term atom to equivalent or proportion, he 

 must submit to the somewhat jarring expression of 

 half an atom. Mr Dalton supposes that the atoms 

 of bodies are spherical, and has invented certain 

 symbols to represent the mode in which he conceives 

 they may combine together. (See his New System 

 of Chemical Philosophy.) There are several ques- 

 tions relative to the nature of atoms, most of which 

 will, perhaps, never be decided. Of this nature are 

 the questions which relate to the actual form, size, 

 and weight of atoms, and to the circumstances in 

 which they mutually differ. All that we know with 

 any certainty is, that their weights do differ, and by 

 exact analysis the ratios between them may be de- 

 termined. The numbers which indicate the combin- 

 ing proportions of bodies, are, in fact, the relative 

 weights of their atoms. 



ATOOI, or ATTOWA, or ATTOWAV, or Towi ; one of 

 the Sandwich islands, in the Pacific ocean ; about 

 thirty miles in length from E. to W., according to 

 some ; others make it 300 miles in circumference. 

 It has a good road and anchoring-place on the S. W. 



