A Sketch of the Atomic Theory.

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their individuality; so that when the compound they form is decomposed, they separate, and reappear with all their original properties. "The smallest possible quantity of water is in this way conceived to consist of one atom of hydrogen and one of oxygen bound together, without loss of the individuality of either, by the unknown and invisible tie which we term chemical affinity."

This brief exposition, divested as far as practicable of unnecessary technicalities, may enable the reader to form some notion of Dalton's great discovery. Dalton's views of chemical combination, including both the facts and the hypothesis which expressed and explained them, are generally known as the "Atomic Theory." Dr Wilson observes :-"To Dalton himself, the evidence in support of the existence of ultimate indivisible particles appears to have seemed so conclusive, that he considered the doctrine of atoms in the light of an induction from the data furnished by observation and experiment, and this without reference to any other than purely physical questions. We cannot sufficiently reiterate that he was an atomist before he was a chemist. In his lips, therefore, the name 'Atomic Theory,' was consistent, and had a clear meaning. It was John Dalton's atomic theory of chemical combining proportions; his theory of atoms connected with his discoveries in chemistry, so as at once to account for, and to expound them. To those, however, who cannot by any process of generalisation establish to their own satisfaction, or to that of others, the actual existence of atoms (and it includes almost every one who thinks on the subject at all), and for whom the

doctrine of atoms is only a questionable, and, we may say, an indifferent hypothesis, Dalton's view is 'an atomic hypothesis of combining proportion.' matters comparatively little, however, whether we say atomic theory or atomic hypothesis, provided we keep perfectly distinct what is matter of assumption concerning atoms from what is matter of fact concerning laws of combining proportion."

In a subsequent chapter a few words will be offered on the influence of the atomic theory in the development of the science of chemistry, and the mode in which the new doctrine was received by the contemporaries of Dalton both at home and abroad. In the meantime some recognition should be made of his social life, and his public appearances as a lecturer in London and the larger cities of Britain.

CHAPTER XII.

"For the highest degree of organization Gives the highest degree of thought."-PARMENIDES.

PORTRAITURE-SOCIAL HABITS-TEACHING AND ITS REWARDSLECTURES AT THE ROYAL INSTITUTION, LONDON-HIS RESIDENCE —HIS RETICENCE ON PUBLIC AFFAIRS-LECTURES IN EDINBURGH GLASGOW, AND LONDON-HIS CORRESPONDENCE ON A VARIETY OF TOPICS.

JOHN DALTON'S stature was slightly above the middle height, say sixty-eight inches. His robust, muscular frame bore considerable resemblance to a class of men daily met with in the agricultural districts of Cumberland. Seen in country garb, and judged from his mere physique, he might have been looked upon as possessing sufficient of the athlete to become a prizewinner in the Carlisle wrestling-ring; nor would his deep, somewhat gruff voice have been an unworthy accompaniment of such bucolic championship. His slight stoop forward, in part arising from his studious and sedentary habits, and unpolished gait, betrayed the absence of physical training; yet after middle age, it appears he could, without a day's preparation, walk as rapidly and continuously as the most disciplined pedestrian; nay, climb the dark brow of the mighty Helvellyn, of three thousand feet, with ease and alacrity.

The real strength and pith of the man lay not in bone and muscle, but in an ample nerve-power and the possession of a fine cerebral development. He had an expressive, thoughtful countenance, and a healthful masculine organisation that could not fail to attract attention. All the portraits of Dalton display a broad, expansive head, bearing no small resemblance to that seen in the engraved portrait of Sir Isaac Newton. And it would appear that the members of the British Association who were present at the Cambridge meeting, in the year 1833, were impressed with Dalton's likeness to Roubiliac's statue of Newton in Trinity College Chapel. Mr Woolley, also an intimate friend of Dalton's, who had a cast of Newton's head placed near Dalton after his decease, has recorded "that the likeness which had been observed during life was in death most striking."

As far as a careful comparison instituted within an interval of four days can be relied upon, I should say the configuration of the head in the statue of Sir Isaac Newton at Grantham resembles very much that of Dalton's standing in front of the Manchester Infirmary. Whether this analogy of form be strictly dependent on the similarity of the crania of the two philosophers, or is in part borrowed from the ideal conception of the sculptors aiming to give breadth to the intellectual organs, is beyond my decision. The statue of Dalton by Chantrey appears to me, both in pose and general treatment, one of his best works. The artist, however, has given undue and unnatural prominence to the part of the forehead immediately above the eyebrows. Among other relics of their

accomplished President preserved by the Literary and Philosophical Society of Manchester, is Dalton's hat, from the shape of which it is easy to see that Dalton's head was of the bracycephalic type, with great width across the temples, or in the tranverse axis of the cranium.

The massive, full contour of Dalton's head impresses you with the stamp of intellectual power, and a capacity for the highest of human efforts; and nobly distinctive as it appeared, it was not a whit more noble in form than the brain-structure it enclosed was in fitting response to those claims which science exacts from her more distinguished votaries. His prominent eyebrows shaded in deeper setting eyes of quiet discernment, whilst the use of large spectacles added to his general philosophic seeming and force of character. In his marked nose, rather massive jaws, and firm, deep chin, you saw the features of the sturdy race of the "north countrie," not altogether free of an air of severity at times; these, however, were somewhat toned down by lips less masculine than usual, and a physiognomy that offered blandness as well as firmness and penetration.

The portrait accompanying this memoir is taken from an admirable likeness of John Dalton by Mr J. Lonsdale, engraved by C. Turner, A.R.A. The original picture was in the possession of James Thomson, Esq., F.R.S., of Clitheroe. In preferring Lonsdale's portrait to that by Allen, or the engraving taken from Chantrey's bust, I am guided by those who knew Dalton long and intimately. There are, it is said, other excellent portraits of the philosopher, whose

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