"An atom of water or steam composed of one oxygen and one hydrogen, &c. = 8," and so on with other bodies.

This is the result of enormous labour, added to that of the many gaseous analyses. Let no one say that because the atomic weights are in most cases inexact he shews want of power. We have seen in our own days how difficult it is to get an exact atomic weight, we have found that it needs the combined forces of several laboratories to settle one to satisfaction, and we must rather admire that man who approached first so near. But, although Dalton has been called a rough worker, and I am not prepared to deny it, we must remember that his analyses are not behind the time, but in advance of it in early life. At the period when he was working out this theory, the analyses of all chemists were in general only approximative. Fine analysis was only then beginning its course. But as Dalton says, "it is not necessary to insist on the accuracy of all these compounds, both in number and weight; the principle will be entered into more particularly hereafter, as far as respects the individual results."*

He also says, "it is not to be understood that all those articles marked as simple substances, are necessarily such by the theory;" ex. gr., soda and potash are mentioned as compound.

In various parts of his work we learn exactly the method in which he applied his theory, and as he devoted his time to its illustration, we are not left in any doubts as to his opinions.

We have now to find exactly what new ideas he produced. We have seen in the last chapter the state of chemical opinion, the prevalence of the Berthollet philosophy, and the uncertainty hanging over the opinions opposed to his. General opinion on combination was in reality not more advanced than in the earliest days of the science. Dalton found matters in this state of confusion, and we have seen the

* Page 220.

results he arrived at, and the process. 1st. By long reflection on the constitution of bodies, especially of gases, he became convinced of the necessity for ultimate particles, divisible or not so. These particles unite together, and form of course a definite compound. If the smallest part is definite, so is the largest. This is the fundamental law of definite compounds. 2nd. Various numbers of atoms may unite-there may be one, two, three, or more-there can be no division of atoms. As large bulks are constituted just as small are, so multiple proportion becomes a law by which bodies are constituted. 3rd. Compound bodies constituted as the above unite particle to particle in a manner exactly similar to simple bodies, and so we have compound proportion, and are led to a mode of inquiry into, and a method of expressing the most complicated bodies. 4th. If we obtain the relative weights of the constituents of bodies we obtain the relative weights of the atoms, because the smallest parts must be constituted as the largest. 5th. The relative weights of the atoms become constant expressions for the proportions of combinations.

These are the fundamental principles which made chemistry a science and hold it together, and although Dalton had no direct help in discovering any of them, we have seen that Higgins had already expressed the first two. Richter and Fischer had made out numbers representing the reciprocal proportion of bodies, and although not going to first principles, and establishing no law, Fischer's numbers adopted by Richter, I believe in 1803, are really atomic weights or equivalents, although they did not see them to be such.

There existed, therefore, in the world material for completing the theory of combination, but there was no one who saw it clearly, and no one who knew both parts published. Dalton cannot be blamed for not knowing them; no one knew them. Although Dalton had to begin without their aid, the custom of the world is to give credit to him who adds to its accumulated knowledge, not to him who obtains knowledge in

his closet merely. By this custom, therefore, Dalton's credit would be the whole theory, minus what Higgins and Richter had done; how much this was who will venture to declare, the two parts being the conceptions of different brains, so that Thomson, with his great quickness, could make nothing out of one, and Berzelius, with his patience, nothing out of the other; nevertheless, Dalton must not have their credit, and it was not the habit of his independent spirit to seek from others. Dr. Henry has made it clear that he had not seen Higgins's book. He no doubt saw Proust's results. They are in the library of the Manchester Society, and they are probably the most likely to have assisted him, as the analyses and reasoning are remarkably clear, but devoid, as before said, of theory; still the clearest and best were later than Dalton. This, therefore, seems to be the result, that although actually producing all the theory within himself, from the world his deserts are that he first saw the great importance of the idea of using atoms to illustrate proportion and definite constitution. He followed up the idea, and found in it a fundamental natural law, as it appears hitherto. He saw the use and importance of multiple proportion, or the adding of atom by atom in twos or in threes, and he proceeded to investigate nature under this impression. He proved that bodies followed laws, such as fitted his hypothesis, which was thenceforth taken into the province of scientific theory. To perform the above it was needful to grasp the idea more firmly than it had been done, to work laboriously, and to decide convincingly. This Dalton did. He then extended this from simple to complex combinations, and gave the first idea as well as proof of compound proportion, laid down the laws orderly into a system, and accompanied the whole by abundant and laborious proofs. He gave the first idea of atomic weights. Under this head came Richter and Fischer's numbers. Richter grappling with those numbers never could obtain a rational theory from the phenomena. Dalton's plan explains these

numbers with the greatest ease, and looks on such as a necessity of the fundamental law, instead of the beginning of the inquiry as it was to them.

It seems to me, then, that what happened historically, happened also intellectually. Dalton had included his predecessors in his more extensive system. He had gone to the summit of the hill, and when coming down, found proofs that they had been making good progress upwards. Higgins had gone at once to the top, as it appears to me, but took no heed to make the needful observations when he was up, or he found the prospect entirely obscured. We are compelled to put reciprocal proportion in a secondary position, as it seems to me it cannot be called a law, but one of the consequences of a law; and the evidence brought to support it, otherwise than empirically, presupposes some of the principles on which the general laws depend.

It was by a careful mechanical juxta-position of parts that Dalton arrived at his idea, it is eminently mechanical, and it is remarkable that all progressive views on that subject have been so. He introduced proportional weight into the theory, and found it to agree with facts. His is, therefore, the quantitative atomic theory. In this complete form no one seeks to take from him the honour. The total is so entirely his, that the disputed parts can be held only as a fealty.*

Although Dalton rigidly held to the idea of atoms, he by no means supposed that we had attained the indivisible atom

* Dr. Schweigger, in his pamphlet, objects that Dalton's theory was not conceived in the spirit of the ancient theory, because he allowed some atoms to be small and some large. Strange this. The reason that the ancient theory is insufficient, is simply because it was not conceived in the spirit of Dalton's. 2nd. Most of the ancients allowed greater and smaller atoms, and various shapes. 3rd. Dalton formed his theory in the belief that atoms were of one size, but afterwards saw reason to change his opinion. Dr. Schweigger, therefore, has forgotten the opinion of Dalton and the ancients, as well as Richter's preface, where he calls the permanent neutrality of neutral salts after neutral decomposition, a well known fact. He sneers at the atomic theory, thinking that by putting it down, Dalton will fall; I don't agree with him there, but there is time enough to wait.

in our elements; at least, he expressly reserved this point. What he speaks of is simply the ultimate particle that seems to act in our chemical processes.

Dalton used atom and particle. Many have objected to both, but they are words which really involve less theory, and are more generally applicable than any yet obtained, except, perhaps, combining proportion, which is too long. Equivalent, Wollaston's word, is itself too long, limited in its meaning at best, and at times either meaningless or incorrect. Whenever we conceive of combining proportion, we reduce the quantity to the smallest conceivable, every portion becomes a unit, and each unit is undivided; it is a particle for the moment, and an atom as far as the effect we study is concerned. Having, after much labour, attained this mode of thinking, we can now scarcely think of compounds otherwise, nor indeed has any other method suggested itself as better, although investigation is promising advance in our knowledge, and will probably some day astound us by its results.

The consequences of Dalton's laws gradually shewed themselves to be, that there was now one great law or theory in chemistry, so that it was for the first time fit to be called a science. Heretofore it was a series of separate facts, and even now we may say that it is more a branch of natural history than of exact science, but as a science it is preserved by this fundamental law and its branches, and by this only. It is stretching itself out in many directions, and its future will undoubtedly be still more brilliant; at present, although it has planted its standard in numerous spots, it has fixed a government on few, but still issues the central law unchanged, although with explanatory extensions. The history of the atomic theory, since Dalton's time, is contained in Dr. Daubeny's work, and on that it is not my desire to encroach, nor could I hope to equal it.

A very little need be said as to the consequences of the promulgation of Dalton's views. They were explained in