removal of that pressure, are mechanically mixed with the liquid, and not chemically combined with it.”

He had already mentioned Dr. Henry's discovery, that the quantity of gas absorbed is as the density or pressure.

"2. Gases so mixed with water, &c., retain their elasticity or repulsive power amongst their own particles, just the same in the water as out of it, the intervening water having no other influence in this respect than a mere vacuum."

"3. Each gas is retained in water by the pressure of gas of its own kind incumbent on its surface abstractedly considered, no other gas with which it may be mixed having any permanent influence in this respect."

"4. When water has absorbed its bulk of carbonic acid gas, &c., the gas does not press on the water at all, but presses on the containing vessel just as if no water were in. When water has absorbed its proper quantity of oxygenous gas, &c., that is, 1-27th of its bulk, the exterior gas presses on the surface of the water with 26-27ths of its force, and on the internal gas with 1-27th of its force, which force presses upon the containing vessel, and not on the water. With azotic and hydrogenous gas the proportions are 63-64ths and 1-64th respectively. When water contains no gas, its surface must support the whole pressure of any gas admitted to it, till the gas has in part forced its way into the water."

"5. A particle of gas pressing on the surface of water is analogous to a single shot pressing upon the summit of a square pile of them. As the shot distributes its pressure equally amongst all the individuals forming the lowest stratum of the pile, so the particle of gas distributes its pressure equally amongst every successive horizontal stratum of particles of water downwards, till it reaches the sphere of influence of another particle of gas. For instance, let any gas press with a given force on the surface of water, and let the distance of the particles of gas from each other be to those of water as 10 to 1, then each particle of

gas must divide its force equally amongst 100 of water, as follows: It exerts its immediate force particles of water; those 4 press upon 9, the 9 up and so on according to the order of square numb 100 particles of water have the force distributed a them; and in the same stratum each square of 100, its incumbent particle of gas, the water below this stra uniformly pressed by the gas, and consequently has equilibrium disturbed by that pressure."

"When water has absorbed 1-27th of its bulk of an the stratum of gas on the surface of the water presses 26-27ths of its force on the water, and with 1-27th force on the uppermost stratum of gas in the water; th tance of the two strata of gas must be nearly 27 tim distance of the particles in the incumbent atmosphere 9 times the distance of the particles in the water. comparatively great distance of the inner and outer a phere arises from the great repulsive power of the latte account of its superior density, or its presenting 9 par of surface to the other 1. When 1-64th is absorbed distance of the atmospheres becomes 64 times the distan two particles in the outer, or 16 times that of the in The annexed views of perpendicular and horizontal stra gas in and out of water will sufficiently illustrate positions."*

"7. An equilibrium between the outer and inner at pheres can be established in no other circumstance than of the distance of the particles of one atmosphere being same or some multiple of that of the other; and it is proba the multiple cannot be more than 4. For in this case the tance of the inner and outer atmospheres is such as to m the perpendicular force of each particle of the former or th particles of the latter that are immediately subject to its in

ence, physically speaking, equal; and the same may be observed of the small lateral force."

"8. The greatest difficulty attending the mechanical hypothesis arises from different gases observing different laws. Why does water not admit its bulk of every kind of gas alike? This question I have duly considered, and although I am not yet able to satisfy myself completely, I am nearly persuaded that the circumstance depends upon the weight and number of the ultimate particles of the several gases; those whose particles are lightest and single being least absorbable, and the others more, according as they increase in weight and complexity (subsequent inquiry made him think this less probable). An inquiry into the relative weights of the ultimate particles of bodies is a subject, as far as I know, entirely new; I have lately been prosecuting this inquiry with remarkable success. The principle cannot be entered upon in this paper; but I shall just subjoin the results, as far as they appear to be ascertained by my experiments."

He then gives a list of relative weights of 21 substances, constituting the first attempt to form a table of atomic weights.

“Table of the relative weights of the ultimate particles of gaseous and other bodies.

I have given as much as possible, in his own wor most important points attended to by Dalton up date. It was not my intention to inquire into the par relating to the novelty of the views taken by him, on the atomic theory, and have therefore purposely any such opinions as might require discussion; nor shewn in all cases where advancing science has differed his results. Some things in the papers alluded to wer and strikingly new, some things are improvements on th some are mere re-statements of the old, but all is don firm, clear, and determined manner, as by a masteri business, going to the real point of difficulty in every and at all times avoiding unimportant details or vain He drives on like a new settler, and clear ground before him, leaving it rather rugged it is nevertheless it is resolutely cleared.

We now approach the most important discovery of Dalton, and before entering upon it, it may be well to acquaint the reader with the general character and appearance of the man in his vigour. It is not my intention, as before stated, to amuse myself or readers with many little incidents of his life, nor can we gain by looking at such a character apart from the student of nature; but it is needful to give some slight account of the appearance and habits of the agent by which such valuable knowledge of natural law has been gained. On his habits, Miss Johns's Journal, lent me freely by Mr. Woolley, is the best authority. The Rev. W. Johns, once a colleague of Dalton's at the academy, had a school in George-street, near the Literary and Philosophical Society, which had given up a portion of its room to Dalton. In the autumn of 1804, Mrs. Johns saw him casually pass, and asked him why he never came to see them. Dalton said, “I do not know; but I will come and live with you, if you will let me." He did so, and took possession of the only bedroom at liberty, sitting with the family. In this family he lived for twenty-six years in the greatest amity, until Mr. Johns, giving up the school, sought a purer air in the suburbs of the

town.

The portrait which is appended to this memoir, is from a picture by Allen, presented to the society by that painter on the occasion of Dalton being made president. It represents him in the vigour of life, and must of course be a more suitable representation of the man than those taken in old age, although one at least of those by Stephenson is an excellent portrait of a late period, and a beautiful engraving.