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mean it to indicate the order of combination, he had in fact made no theory, at least found no law on the subject, although he clearly saw that it must be owing to some law of nature. He fought for constant proportions in combinations, and fought well, but he had no idea of a constant quantity of oxygen found uniting with a constant quantity of every metal, and making higher oxides by steps always of an equal altitude, although he proved that the rise was not that of an inclined plane, but by “fixed terms.” And yet it follows as a consequence, so closely in fact does it follow, that we must put ourselves in the position of the early chemists of the century well to understand the difference. When we have taken that position, we then see how thin was the veil, although utterly impenetrable, that divided his opinion from the present, and prevented the acute, active, and logical mind of Proust from attaining to the great discovery. His determinate proportions are given as remarkable facts, in connection with which he confessed to perceive no law.

Had such men studied Higgins, we should probably never have heard of this controversy, but he was not studied. We may therefore learn not so readily to blame a man for want of honesty, when he publishes for a discovery what has been known before. The most indefatigable workers of the period had neither read Higgins nor Richter. Besides, scientific men like other men are led by fashion, the follies of some men become great discoveries for a while, and the wisdom of men comparatively obscure, such as the two mentioned, is neglected or sneered at. Yet the whole body endeavours to acknowledge facts only.

As a specimen of the chemical books of the time, let us take one published in the same year as Dalton's work on the atomic theory, although after Dr. Thomson had made it public, “A Course of Theoretical Chemistry, by Friedrich Stromeyer.'

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* Grundriss Theoretischer Chemie zum behuf Seiner Vorlesungen entworfen von D. Friedrich Stromeyer. Göttingen, 1808.

He says, p. 66, § 36, “ The affinity of a substance towards another is always in proportion to its chemical mass, which it brings with it for combination.”

Page 68. “ Affinity is consequently in no way an elective attraction, in the sense in which Bergman and his followers have taught it."

Page 80, $ 59.“ By means of affinity alone two substances may combine with each other in every quantitative proportion. Although this asserts quite the opposite of Bergman's theory, and even appears to contradict experience, it is nevertheless a perfectly natural consequence of the above.

“For suppose A and B could combine in the proportions of 5 : 7, and not as 10 : 7, if we put 7 parts of B with 10 of A, then the very same thing would happen as when we put 7 parts of B with 5 of A; that is, the 7 parts of B would combine with 5 parts of A, and the other 5 parts would remain uncombined.

“ If this were really possible, then it would follow clearly that 10 parts of A contained no more affinity than 5 parts, which however completely contradicts what is proved in § 36."

The idea of the present law seems to have entered into his mind as a conclusion to be avoided for its absurdity.

$ 60. “ But as soon as the power of cohesion or expansion of two substances of a given mass, acting on each other, ceases to be overpowered by their affinity, an exception constantly takes place to this universal law, and a certain proportion of mixture is established between the two substances, which, on account of their affinity, can no longer be surpassed, and consequently limits their mutual affinity.

" But if there were a removal of the obstructions caused by cohesion and expansion to the affinity of two bodies, then the law would again come into action in its first unity.”

“ The absorption of several gases by water, the solution of salt in water, and the oxidation of metals, best establish that which has been said."

$ 61. “ This general law is subject to an exception also, when there is a change of the aggregate condition during the action of two or more substances, and in this case also a combination takes place of a fixed proportion.”

Here we have a clear account of the direction that Berthollet's teachings gave, and the consequences are logically deduced. Here, too, we find that fixed proportions are obtained as exceptions, but it is also seen how needful it was to have them occasionally in order to explain facts in the science.

Stromeyer's words do, in fact, represent the confused and contradictory opinions of the time, and afford us another proof that no one before Dalton had given opinions sufficiently authoritative on the atomic theory to be retained by the teachers of chemistry; and we may add also, none deemed of sufficient importance to demand at the time very serious discussion.

This want of attention, even to imperfect theories, arose mainly, I believe, from the fact, that those theories hitherto given had not had accumulative scientific proof to give them force in the world ; they had organized no executive force. Chemists, generally, had not arrived as far as the inquiries already quoted.

It was intended to give a number of similar instances, to show how entirely all atomic theories and theories of definite proportions were out of the boundaries of general chemical science when Dalton published. I happened to take up Stromeyer first; many instances occur in our own country, but this will probably be found sufficient.

CHAPTER XI.

DALTON'S ATOMIC THEORY.

We now come to Dalton, whom we have left since he first thought of weighing atoms; this has been done in order that by accumulating all the materials he might have used, we may know what has been his especial work. Matters stood thus : Higgins had, in 1789, seen the fundamental principle clearly, and given it out more as a thinker than a discoverer, neglecting to generalize; that principle included simple proportion or the law of necessary definite composition and multiple proportion. Richter had systematized all the laws of combination known to him, but had not known of Higgins, although he would there have got the clue to all his strivings. He discovered one of the most important consequences of the fundamental law, in reciprocal proportion, but did not rise up to first principles. Scientific men could get no decided guide from either, and preferred to follow Berthollet, who was leading them out of the right direction, obstructing for many years the advance of chemical philosophy, or compelling others to accumulate proof until it was sufficient to overwhelm him.

The materials we have for tracing the progress of Dalton's opinions are few, but distinct and sufficient. I shall not enter into the argument of honesty, which can be thrown with greater violence at so many heads, but shall take it for granted, that all those who have had the honour of working at the laws of chemical combination with any success, have also had the advantage of an honest mind. I know of no dishonesty on any side among the principals connected with this subject, and their defenders have erred, probably, on account of proving one side better in morals than the other.

From the earliest period of his scientific life Dalton had been accustomed to think carefully on the constitution of the atmosphere; this is seen as early as 1793, in his meteorology. This subject continued to be a favourite one, and led him to gases generally. The experiments quoted at p. 43, on nitrous gas and oxygen, and those mentioned afterwards in a quotation from Dr. Thomson, shew the method by which he came to believe, and to prove experimentally, the existence of definite and constant proportion.

Here lies the difference between him and Higgins. Higgins expressed the fundamental idea as clearly as Dalton, but it was still left uncertain. Dalton proves it by experiment, draws the conclusion, and tells us the “ theory” in a few lines. We have then distinctly the method by which he came to believe in definite proportion and multiple proportion. He proved them for himself, and theorized for himself. No books of any writers before him, no Proust or Berthollet controversies were so decisive as these few experiments of Dalton; not clearer than the words of Higgins, but more decisive, because the result of observation and of reasoning combined. This seems to have been his first direct entrance into the region of the atomic theory.

In reading over his earlier works, or even in reading the short account here given, we may remark with what a firm grasp he lays hold of the existence of atoms, of the idea that all matter is made up of separate ultimate particles, divisible or indivisible. We find no scientific man holding the idea with such firmness; to others it was a theory, to Dalton it was a fact, which he could not conceive otherwise. We find that even the air is represented* as an agglomeration of bodies heaped up like piles of shot. We appear to be entirely removed from the region of speculation when reading his words; although he leads us farther than the most fantastic speculator had done, the road is made so clear before us, that

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