complexity of compounds will be found in the atmosphere of the fourth class." 14 After the publication of Newton's Optics in 1704, the history of this branch of science was almost a blank in Britain, till 1803, when the researches of Dr. Young on the undulatory theory of light appeared; and since the subject has been treated with increasing interest and success. Sir David Brewster, 15 who attained distinction in this branch of science, and in other fields of intellectual effort, was a native of Jedburgh, He was educated at the University of Edinburgh, and had the advantage of the instruction of Professor Robison, and other eminent teachers who then spread the rays of light with consummate ability. He devoted himself to science; and in 1805, he edited Ferguson's Lectures on Astronomy; and, as already mentioned, he commenced the Edinburgh Encyclopædia in 1810. His first separate work, On New Philosophical Instruments, appeared in 1813, which also contained observations on refractive and dispersive powers. From this date onwards he became a regular contributor to the London Philosophical Transactions, and also those of Edinburgh; he commenced the Edinburgh Philosophical Journal and the Edinburgh Journal of Science. His contributions to scientific societies and journals. would fill many volumes. One list of his scientific papers extends to the number of three hundred and fifteen, and the following is only the briefest indication of some of the more important subjects treated in them : (1) "The Laws of Polarisation by Reflection and Refraction, and other Quantitative Laws of Phenomena;" (2) "The Discovery of the Polarising Structure induced by Heat and Pressure;" (3) "The Discovery of Crystals with Two Axes of Double Refraction, and many of the Laws of their Phenomena, comprising the Connection of Optical Structure and Crystalline Forms;" (4) "The Laws of Metallic Reflection;" (5) "Experiments on the Absorption of Light." The more important of his other works are (1) A Treatise on the Kaleidoscope, published in 1819; (2) A Treatise on Optics, 1831; (3) A Treatise on the Microscope; (4) A Treatise on the Stereoscope; (5) an Article on "Magnetism," reprinted from the Encyclopædia Britannica; (6) The Martyrs of Science-Galileo, Tycho Brahe, and Kepler; (7) Life 14 Recent Advances in Physical Science, by P. G. Tait, pp. 230-231. 15 Born in 1781; died in 1868. of Sir Isaac Newton; (8) Letters on Natural Magic; (9) More Worlds than One. He also wrote a Life of Euler and edited his Lectures; edited Robison's System of Mechanical Philosophy, with a preface and notes, which appeared in 1822, in four large volumes; he also contributed seventy-four articles to the North British Review. This enumeration of his writings, though far from complete, is sufficient to show his great mental energy, and his scientific and literary talents. He was a man of remarkable intellectual resource, his imaginative and elaborative faculties were of a high order, and, for industry and observation he has rarely been surpassed. His style is clear and flowing, he has a copious command of expressive language. Besides his discoveries of the law of polarisation, of biaxal crystals, of optical mineralogy, and of double refraction by compression, he invented a dioptric apparatus for the illumination of lighthouses, which he described in 1812. In 1820, he endeavoured to get the dioptric system adopted, but failed; at length, however, on the motion of Mr. Hume, a Committee of the House of Commons was appointed to consider the subject; and, in 1836, this system was applied to a Scotch lighthouse, and has since been universally extended. In 1816, he invented the kaleidoscope, which soon became popular over Europe; afterwards, he made an important improvement on the principle of constructing stereoscopes. In the words of Professor Forbes-"Few persons have made with their own eyes so vast a number of independent observations; few have ever observed better, or recorded their observations more faithfully." He was an honour to his country and a benefactor to mankind. In the interesting science of the earth-geology-Dr. Hutton, in 1788, enounced his theory that the changes in the earth's crust have been mainly caused by the agency of fire; but though his views were ingenious and well argued, they have long ago been superseded by conclusions more in accordance with the observed phenomena. This branch of knowledge has been much investigated in the present century, and several Scotsmen have attained distinction in advancing it. Sir Charles Lyell 16 was a native of Forfarshire, and studied at Oxford. His Principles of Geology, being an attempt to explain the former changes of the earth's surface by a reference to causes now in 16 Born in 1797; died in 1875. operation, appeared in 1830-32, in two volumes. He made additions to it, and alterations from time to time, and the eighth edition of the work, thoroughly revised, was published in 1850. Though he recog nised new facts, he continued to hold his theory that we may dispense with sudden and general catastrophes, and consider the past and present fluctuations of the organic and inorganic world as forming one continuous and regular series of phenomena. In 1838, he published his Elements of Geology, which was afterwards enlarged to two volumes. He is also the author of Travels in North America, with Geological Observations on the United States, Canada, and Nova Scotia, published in 1845. He was twice elected president of the Geological Society, and he received the honour of knighthood in 1848. His style is attractive, easy, and fluent, and his writings were popular. The following is a short specimen of his manner : "The analogy, however, of the monuments consulted in geology, and those available in history, extends no further than to one class of historical monuments-those which may be said to be undesignedly commemorative of former events. The canoes, for example, and stone hatchets found in the peat bogs afford an insight into the rude arts and manners of the earliest inhabitants of our island; the buried coin fixes the date of the reign of some Roman emperor; the ancient encampment indicates the districts once occupied by invading armies, and the former method of constructing military defences; the Egyptian mummies throw light on the art of embalming, the rites of sepulture, or the average stature of the human race in ancient Egypt. This class of memorials yields to no other in authenticity, but it constitutes a small part only of the resources on which the historian relies; whereas in geology it forms the only kind of evidence which is at our command. For this reason we must not expect to obtain a full and connected account of any series of events beyond the reach of history. But the testimony of geological monuments, if frequently imperfect, possess at least the advantage of being free from all suspicion of misrepresentation. We may be deceived in the inferences which we draw, in the same manner as we often mistake the nature and import of the phenomena observed in the daily course of nature; but our liability to err is confined to the interpretation, and, if this be correct, our information is certain." Sir Roderick Murchison, 17 a distinguished geologist, was a native of Ross-shire, and served in the army from 1807 to 1816. 17 Born in 1792; died 1871. He directed his attention chiefly to a series of strata in the district bordering on England and Wales, inhabited in early times by the British tribe of the Silures; and after working four years in classifying the rocks and deposits, he separated them into four formations, and showed that each is characterised by peculiar organic remains : and, in 1835, he divided them into a lower and upper group, both of which he anticipated would be found applicable to wide regions of the earth, and named them the Silurian System, the details of which he published under this title in 1839. In 1854, his later researches were published under the title of Siluria: the History of the Oldest Known Rocks containing Organic Remains. He spent many years in Russia and in other countries in geologic explorations; and, in 1846, he published The Geology of Russia and the Ural Mountains, in which he was assisted by Count A. von Keyserling and E. de Verneuil. He is also the author of upwards of one hundred separate memoirs presented to scientific societies. In 1844, after examining some specimens of Australian rocks brought to this country, and comparing them with those of the auriferons Ural Mountains, he came to the conclusion that gold existed in Australia. Two years later, he urged the Cornish tin miners to emigrate to the colony of New South Wales, where they could obtain gold from the alluvial soil in the same way as they extracted tin from the gravel of their own country. The following is a summary of the Siluria strata as they occur in the district mentioned above, upon which Sir Roderick mainly founded his system; they represent a thickness of about nine thousand feet : Upper strata. Lower strata. Finely laminated reddish sandstone and shales. Calcareous shale, with concretions of limestone. Concretionary limestone and argillaceous shale. Gritty sandstones and shales. Grits and sandy shales. Thick-bedded white freestone. Dark-coloured flagstones and slates. Dark-coloured calcareous flags, bands of limestone, and gritty flagstones. Excepting a few indistinct fragments of land plants in the uppermost beds, the whole remains are characteristically marine, and evince conditions favourable to a variety of invertebrate life. Among the prevailing and distinctive fossils are fucoids or seaweed plants, corals, radiate animals, sea-worms, and shell-fish in great variety. And strata characterised by these fossils are largely developed in many countries, especially along the flanks of the older mountain-chains. "They occur in Wales, in Cumberland, in Westmoreland; along the south of Scotland; south-east of Ireland; the south of France, Spain, Scandinavia, Russia, and Bohemia; in Asia Minor; along the Himalaya and Altai ranges; in Australia and New Zealand; along the Andes, Rocky Mountains, and Appalachians in America." I have already mentioned Hugh Miller as a geologist, and no one was more ready than Sir Roderick Murchison to recognise his merits and to applaud his genius. Murchison received the honour of knighthood in 1846. The first editor of the Scotsman, Mr. Maclaren, was a student of geology, and published an Account of the Geology of Fife and the Lothians in 1839. It was, however, Hugh Miller that made geology popular in Scotland, and gave a great impulse to its study. SECTION II. Progress of Mechanical Science. The relation between physical science and the mechanical arts are obvious in many ways. The exact boundaries between science and art are as undefinable as those which separate the kingdoms of nature from one another. If there are arts that cannot be called scientific, there are others which have contributed more to the store of knowledge than they ever drew from it, as the progress of science must be gathered from the records of experience, and in order to understand its importance, we must consult many of the varied pages of this record. In the progress of physical and mechanical science, as in that of social science and civilisation, the retarding obstacles everywhere mainly consist in the want or the imperfection of the requisite means-for observation, experiment, and verification in the former, for organisation and just and mutual union in the latter; in both spheres the chief retarding causes are the lack of appropriate and available means at the time and place when they were most |