While an impulse was thus given to the mathematical theory of light in the University of Cambridge, similar progress was being made in the sister University of Dublin, where three of her most eminent professors—Sir William Rowan Hamilton, Dr. Lloyd, and Mr. M'Cullagh—devoted themselves energetically to its improvement and verification. Sir William Hamilton, a geometer of the first order, having undertaken a more complete discussion of the wave surface of Fresnel, to the equation of which he gave a more elegant form, ascertained the exact nature of that surface, and consequently the exact direction of refracted rays in the neighbourhood of the optic axes. The beautiful and unexpected results he obtained were verified by his friend Dr. Lloyd. The names of Sir William R. Hamilton and Dr. Lloyd will be handed down to posterity in connection with this discovery. "But," says Professor Forbes, "they have other claims to our respect. The former has generalised the most complicated cases of common geometrical optics, by a peculiar analysis developed in his essays on 'Systems of Rays.' To Dr. Lloyd we are indebted for several interesting experimental papers on optics, for an impartial review of the progress of the science, and for an excellent elementary treatise on the wave theory."

In the galaxy of illustrious names that shed light upon this age, not the least conspicuous is that of Mary Somerville, who is known in British science not only as the able commentator of Laplace's "Mécanique Céleste," but as the author of some ingenious experiments on the magnetising power of the violet ray, and on the permeability of different bodies to the chemical rays, similar to those of Melloni on the heating rays; and she found great and seemingly capricious variations in this respect. The beautiful invention of the stereoscope, one of the most interesting contributions made to the theory of vision, was the work of Mr. Wheatstone, who published an account of it in the "Philosophical Transactions" of 1838. In connection with experiments of this class should be mentioned the invention of the daguerreotype, or the production of permanent pictures on plated copper, in 1825, which was brought to perfection in 1839 by Daguerre, whose name it bears. About the same time Henry Fox Talbot applied himself to similar experiments, and invented the calotype, or the production of permanent pictures on paper; and by a subsequent invention he obtained what he justly called "an instantaneous process." The science of photography was, however, in its infancy.

But far more important are the wondrous powers evolved from the study of heat. The pioneer in this branch of work was the Hon. H. Cavendish, who was born in 1731, and devoted his life, until his death in 1810, to the pursuits of science. He was followed by Dalton, who made several important discoveries in chemistry, particularly with reference to the gases, and in the doctrine of heat. With the greatest modesty and simplicity of character, he remained in the obscurity of the country, neither asking for approbation nor offering himself as an object of applause. In 1833, at the age of sixty-seven, he received a pension from Government, which he enjoyed till 1844, when he died. His discoveries may be said to have terminated at the age of forty, though he laboured for thirty years after. His first sketch of the atomic theory was propounded as early as 1807.

Sir Mark Isambard Brunel, a hero of mechanical science, made a great step in advance by the invention of self-acting machinery to supersede the work of artisans, by which a new epoch was created in art. The greatest effort of Brunel was the Thames Tunnel, a structure of perfect firmness and solidity laid on a quicksand, and forced through a quaking mass of mud, which will endure like the cloacæ of regal Rome, when the palace and the cathedral have crumbled to dust. He was enabled to accomplish this prodigious work by means of "the shield"—a movable vertical frame of cast iron, provided with thirty-six cells, in each of which a man was placed with a pick to excavate the area, this frame or shield being moved bodily forward by powerful screws, while the bricklayers brought up the arched masonry behind, which was then beyond the power of injury. The works, however, were several times "drowned" during their progress by the irruptions of the Thames, but every fresh difficulty was met successfully by the heroic engineer. The tunnel was commenced on the 2nd of March, 1825, and finished on the 25th of March, 1843. Brunel survived the completion of this, his greatest work, above six years, dying on the 12th of December, 1849.

Mention must be made of the extraordinary calculating machines of Charles Babbage. A few years after leaving college he originated the plan of a machine for calculating tables, by means of successive orders of differences, and having received for it, in 1822 and the following year, the support of the Astronomical and Royal Societies, and a grant of money from Government, he proceeded to its execution. He also in 1834 contrived a machine called the "analytical engine," extending the plan so as to develop algebraic quantities, and to tabulate the numerical value of complicated functions, when one or more of the variables which they contain are made to alter their values; but the difficulties of carrying out this plan became insurmountable. In 1839 Babbage resigned the professorship of mathematics in the University of Cambridge. He died at the end of 1871, having devoted his life to the study and advancement of science.

Joseph Mallord William Turner (born in 1775) has been pronounced as "essentially the great founder of English landscape painting, the greatest poet-artist our nation has yet produced. He excelled in everything—from the mere diagram and topographic map to the most consummate truth and the most refined idealism. In every touch of his there was profound thought and meaning." He was unrivalled in storms; as Napoleon said of Kleber, "He wakes on the day of battle." The remark of Admiral Bowles, when looking at Turner's "Wreck of the Minotaur," conveyed the highest compliment to his art—"No ship could live in such a sea." His "Man Overboard" is a still higher effort of genius, in conveying an expression of horror and utter despair. He was the best illustrator of our national poets. He made known to Englishmen the beauties of their native land, and made them acquainted with the picturesque on the Continent. He gave our young artists love for colour, and made us the Venetians of the modern school. From "The fighting Temeraire tugged to her last Moorings," to "Wilkie's Burial," and the "Burning of the Houses of Parliament," he let no event of his age pass without record or comment. He died in 1851.

JOSEPH MALLORD WILLIAM TURNER. (After the Portrait by C. Turner.)

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The fame of Sir Thomas Lawrence (b. 1769) had attained to its meridian in this period. In portrait painting he was one of the most distinguished artists of the day, and he attained proficiency in it without having gone to Italy or studied the old masters. It has been said of him, as well as of Sir Joshua Reynolds, that he painted three generations of beauties. He went to Aix-la-Chapelle in 1818, by invitation, to take the likenesses of the most distinguished statesmen who were there assembled for diplomatic purposes. During his residence on the Continent he was received by the Sovereigns of the different countries he visited, and entertained with marked distinction; and the propriety and elegance of his deportment, we are told, made an impression highly favourable to his character. On his return he found that he had been unanimously elected to succeed West as the President of the Royal Academy, and this office he continued to hold till his death, which took place on the 7th of January, 1830.