The True Structure of Glacier Ice Undetermined.

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2. If the laminated structure of glacier ice is produced by pressure, pressure ought to produce in porous ice, or in ice similar to the nevé, compact ice with planes of bubbles or cavities; but this experiment, though a true test of the theory, has not been made.

3. In the third place, no experiments have been made on the optical structure of glacier ice, or even of Wenham ice, before and after compression. So early as 1813, Sir David Brewster showed that ice was a uniaxal crystal, "from its not depolarising light incident upon it perpendicularly," and giving the coloured fringes when the incidence was oblique. When a thicker piece of ice was used, the system of positive uniaxal rings was finely exhibited. When ice was formed under constraint, as in narrow vessels, or upon a ruffled and agitated pool, its crystallisation was of a composite character, like that shown in fig. 1 of Professor Tyndall's paper.

4. The examination of glacier ice, and also of Wenham ice and porous ice, by polarised light, is absolutely necessary in the future study of glaciers. If the compact blue ice containing the planes of cavities is uniaxal, the optical axis being perpendicular to these planes, and if the same structure does not exist in compressed Wenham ice, the theory of the veined structure is refuted; and if the two structures are similar, its probability is increased. If the compact ice is produced by pressure on the nevé, which, of course, has a composite crystallisation, and a quaquaversus polarisation, we cannot believe that pressure will give it the uniaxal structure. With a differential sliding motion, pressure may operate like traction on crystalline powders, and may, as in Sir David Brewster's experiments, produce, locally at least, a uniaxal structure, in which the axis of the elementary rhombohedrons or hexaedral prisms are dragged into parallelism.

5. As hard substances, such as glass, receive, according to Sir David Brewster's experiments," the polarising structure temporarily by pressure, and as regularly crystallised bodies have their polarising structure increased or diminished by pressure, it will be easy to subject to this test the opinion of Professor W. Thomson, that the pressure to which porous ice is exposed will be increased in the solid ice "all around any two cavities, and nearly in a line perpendicular to the direction of pressure; the increase of pressure being in the plane perpendicular to the pressure, though nowhere so much as in the part between them." This increase of pressure, if it exists, will be shown in polarised

1 Phil. Trans. 1814, pp. 214, 215.

2 Phil. Trans. 1858, Part I., or Phil. Mag., vol. xvi., p. 338.

5

This suggestion was made in the Edin. Review, July 1844, p. 140.

Edin. Trans., vol. xx., p. 155, or Phil. Mag., vol. vi., p. 260.

· Phil. Trans., 1816, p. 156.

light; and, indeed, it is only under its searching analysis, and with the aid of the microscope, that we can study with any success the true structure of glacier ice and of blocks of Wenham ice under pressure.

As the phenomena of glaciers cannot fail to be the subject of continued study and research, we venture to throw out some views which may be useful to the student. It does not seem to have occurred to any of the writers on Glaciers, that great changes may take place in their structure from decomposition alone. In a mass of pure ice formed on the surface of still water, and perfect in its optical structure, decomposition will not take place if it is kept dry and at a uniform temperature. The molecules are in their right place, and external influences alone can disturb the forces of aggregation by which they are held together. But if compact ice is formed by pressure from pure snow, or ice in the state of nevé, or from fragments of perfectly uniaxal ice, the ice must be a congeries of crystals, in which the molecules, lying with their axes in every direction, have a tendency to resume the position which they hold in the perfectly uniaxal crystal; and in a certain time either return to that position, or release themselves from their state of constraint, and perhaps form a laminated structure. Such a change is finely seen in the decomposition of circular crystals, in which the molecules, forced into a position of unstable equilibrium, have their natural tendency to unite their similar poles, assisted by every mechanical vibration, and every variation of temperature to which they may be exposed.*

But there is another species of decomposition which may be usefully studied in reference to the structure of ice, namely, that which takes place in glass and other solids which have been formed by the fusion of crystalline ingredients. In ancient glass the decomposition takes place at an infinite number of points, and produces a finely laminated structure, in which the laminæ are not only separable, but will admit between them water and other fluids. It is quite possible that the cleavage of slates and other rocks may be produced by the same cause, and that Professor Sedgwick may have correctly attributed it to the action of polar forces after the mass had been consolidated. When pressure has produced a laminated structure in wax or in ice, it can only have done this by bringing the molecules within the sphere of their polar forces.

3

The reader is referred to an experiment with the microscope on an ice cavity containing air and water, described in the Edin. Trans., vol. x., p. 26. 2 Edin. Trans., vol. xx., p. 622.

This species of decomposition is fully described by Sir David Brewster in Layard's Discoveries in Nineveh and Babylon. App., p. 674.

Geolog. Trans., 2d ser., vol. iii., p. 477.

Patrick Fraser Tytler.

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ART. VI.—The Portrait of a Christian Gentleman: A Memoir of Patrick Fraser Tytler, Author of the "History of Scotland." By his Friend, the Rev. JOHN W. BURGON, M.A., Fellow of Oriel College, Oxford. London: John Murray. 1859.

THIS is a very pleasing and delightful volume of biography, under a quaint, and, some will think, affected title. The Portrait of a Christian Gentleman suggests ideas of an exclusive and superfine character. All genuine Christian qualities are manly rather than gentlemanly. They are transformations of the man, lustrous lights and "beauties of holiness," wrought into the very tissues of the human structure, and no mere adornments of the gentleman, although in him they may assume a softer and more delicate colouring. We confess, then, that the quaint exclusiveness of the title did not attract us to this volume. We still think that it would have been better without this ornamental device or figure-head; but, after perusing the memoir, we can understand how such a title should have occurred to the author without any feeling of affectation mingling with the affectionate and reverent impulses of his admiration towards the subject of his sketch.

Patrick Fraser Tytler was a man whose life exactly merited such a graceful, quietly interesting, and brief record as this. He was not a great man; he did not exert any powerful influence by his life or by his works; he did not give any new character, or even any fertile and significant impulse, to those historical studies to which he devoted himself. But he was a

good and eminently worthy, and, in his way, distinguished man, who achieved a definite historical work of no mean magnitude, and has consequently associated his name permanently with that of his country. An enlarged biography of such a man, in several volumes, after the approved modern fashion, would have been peculiarly inappropriate. There are few instances, indeed, in which the impropriety of such extended biographies has not been plainly manifest. In the case of our author, however, the very idea of such a thing would have been preposterous. A life of tranquil, domestic interest, and of almost uninterrupted literary labour, combined with the ordinary social enjoyments that fall to the lot of a man of refined tastes in comfortable if not luxurious worldly circumstances, could only have been narrated in several volumes at an expense of superfluous detail and of wearisome disclosures, that must have brought discredit to the author, and offence and disgust probably to the reader. Instead of this, we have just what was needed-as much and no more—and we

thank Mr Burgon for it. We have in ample detail-informing, but almost never obtrusive-such facts as enable us fully to understand the exemplary, laborious, and, in many of its features, beautiful life which he depicts. A clear, harmonious, and comprehensive impression is left on the reader's mind. The "Portrait" grows into distinctness as he proceeds; its lines fill up, and its colours glow with a richer meaning; and the result altogether is, that the volume is one of the most pleasant, interesting, and, we may say, edifying, that we have met with for some time.

Patrick Fraser Tytler was the youngest son of Alexander Fraser Tytler, known as Lord Woodhouselee, and author of the "Universal History" published in Murray's Family Library, and which still retains perhaps the most honoured place among a class of writings pleasing to our grandfathers, but not likely to reappear in the world of letters. Lord Woodhouselee was a man of varied accomplishments, of faithful and upright character, and of warm heart. He had been brought up in the centre of the old literary society of Edinburgh represented by Robertson, Hume, and others. His father, William Tytler, not only mingled in this society, but took an active part in the discussions and interests which animated it. He was distinguished especially by his spirited defence of Queen Mary against what he considered to be the aspersions of these famous historians. His "Inquiry, Historical and Critical, into the Evidence against Mary Queen of Scots," ran through several editions, and drew the attention of such critics as Dr Johnson and Smollett. Dr Robertson took his strictures in very good part; the rival authors continued to live in great harmony and cordiality, and "when Mr Tytler dined at Dr Robertson's house for the last time, he had the pleasure of seeing there Queen Mary's portrait, supported on one side by the portrait of his entertainer, and on the other by his own." David Hume was by no means so complaisant. He attacked Tytler bitterly in a note to his history; and, if a story told in the present volume is entirely to be credited, carried his resentment to a pitch at once unphilosophical and ridiculous. The story is told by the son, Lord Woodhouselee. "One evening, my father and I went to drink tea with his friend, Mr Middleton of Seaton, and Lady Di, at their house in Nicolson Square. On entering the room, the only stranger there was Mr Hume, who, the moment my father appeared, rose abruptly, took his hat and cane, and walked off without saying a word. When he was gone, Mr Middleton said to my father, 'You have fairly put him to flight, for he came but a few minutes before you, and meant to pass the evening at whist. What a terrible little man you are, that can discomfit such a Goliath!' 'Ay,' said my father, the Philistine boasted, but I smote him in the forehead.""

Whatever we may think of William Tytler's prowess in this particular matter-and we confess a smile is apt to steal over us as we think of his complacency on the subject-there can be no doubt that the remarkable talents for historical research which were destined to show themselves in the son and grandson, were, in a conspicuous degree, first manifested by him. The historical distinction of the family began with him; and no less the peculiar type of intellectual and moral character which we see to run throughout the family. Keenness and refinement, and patience of research, without any great strength or insight; and, above all, a sweetness and tenderness of domestic affection, which make their lives beautiful, and invest them with by far their most attractive and exalted interest. We cannot refrain from quoting, as evidence of this latter trait, the following entry, which he made at the age of seventy-four (1785), on the blank leaf of his Bible, in the retrospect of his wife's death two years before. The passage is remarkable in itself, but particularly so in the light which it reflects on the family character :—

"I thank God the anguish of heart, the bitterness of grief, is past. Still, still, however, I deplore her loss, which nothing can now supply. The most pleasant moments in my life at present are in calling up in my mind our mutual endearments, and the bliss and domestic happiness we enjoyed together. I say it with truth, that in the above space of time, since our separation, she has never been one hour absent from my mind. She is the first idea that strikes my waking thoughts in the morning, and the last that forsakes me in sleep. On entering my home after a day's absence, my heart, which formerly used to be elated, now shrinks within me, while I look in vain for the sweet figure that used to welcome me by flying to my arms. Those sparkling eyes, those ardent looks, I no more behold. That sweet voice, her fond exclamation, 'Well, how is my Willie?' still vibrates in my ear."

Trained by such a father, we can the more readily appreciate the character of Alexander Fraser Tytler, and the delightfulness. of that home at Woodhouselee into which we get so many glimpses in the present volume. For these glimpses we are mainly indebted to the pen of the sister of the historian, herself distinguished in the world of letters-Miss Ann Fraser Tytler. Nothing can be more happy than the easy and quiet flow of her style, nothing more minute and yet gentle than her touch, as she describes for us the early years of her brother, and the charming influences, intellectual and social, amidst which he grew up. Patrick was the youngest son of a family which consisted of four sons and three daughters. "As a boy he was in no way remarkable, except for the invariable truthfulness, openness, and perfect simplicity of his character. In acquirements he was