pursuit of knowledge under difficulties. He was apprenticed as a silk weaver, and spent the earlier years of his life in this trade. His scientific tastes were developed in boyhood, but it was not till he reached his fifteenth year that he read any professedly scientific work. It was his amusement to construct quadrants, draw geometrical figures, and resolve arithmetical problems. He was, however, favourably circumstanced for the development of his genius. The Spitalfields weavers, at that time distinguished for their general intelligence and love of mathematical science, had formed themselves into a learned society, which gained a wide celebrity. Young Dollond shared their enthusiasm, and diligently improved his opportunities. He devoted all his leisure hours to the study of mathematics and the applied sciences, especially optics and astronomy. While this department of knowledge chiefly occupied his attention, he aimed at a general intellectual culture, and studied Latin, Greek, theology, and anatomy. All this was done while he industriously worked at the loom. In 1752 he formed the resolution of abandoning the trade of silk weaving for that of the optician. He at once directed himself to the task of improving the construction of the refracting telescope; opticians having hitherto devoted themselves to the improvement of the reflecting telescope, in consequence of the decision of Newton, that it was hopeless to attempt the perfecting of the former. Newton held that the dispersion of light, or the resolution of the white ray by refraction into its component colours, was an ineradicable defect. Dollond lived to refute this opinion. There were two grand defects in the refracting telescope at his time—spherical and chromatic aberrations; the one arose from the spherical form of the lens, this form being a structural necessity. The defect was met, not by altering the form, but by combining lenses so as to effect a compensation by balancing opposite aberrations. The fame of Dollond, however, rests chiefly on the correction of the chromatic aberration. When a white ray is bent by refraction, it is resolved into its component colours. The white ray may be compared to a closed fan, and refraction to the opening up or dispersion of the rays of the fan. Newton assumed—and it was on this assumption he maintained the hopelessness of the improvement of the refracting telescope—that whatever the refracting medium may be, the dispersion or opening out of the colours must be the same in amount if the angle of refraction be the same. Dollond's grand discovery was, that media might be obtained which refract the white ray equally, and at the same time disperse it unequally. He showed that flint and crown glass fulfilled this condition, and that the property might be so applied as to correct the defect of colour in telescopes. The object glass, instead of being formed of one piece of glass, was now composed of two pieces; one being flint, the other crown glass. This grand discovery formed an era both in optical and astronomical science. The claim to the merit of the discovery has been disputed, but all such claims have only resulted in establishing more firmly the right of the Spitalfields weaver. Dollond died in the midst of his labours and his honours. While reading a memoir of Clairaut on the theory of the moon, he was seized with apoplexy, and survived only a few hours. Though constantly engrossed with mechanic labours, he found time to contribute several valuable papers to the Philosophical Transactions.—W. L. M.
DOLLOND, Peter, son of the preceding, was born in London in 1730. He, like his father, served an apprenticeship as a silk weaver. He learned the trade under the eye of his father, and at the time shared in his scientific studies. It was to gratify the wishes of the son that the father opened a shop as an optician, and so far he may be regarded as the founder of the house. The brother, John, was admitted into the firm in 1766, and at his death in 1804, his nephew, George Huggins, took his place. This latter changed his name to Dollond, and for many years sustained the fame of the firm by executing first-class instruments. Peter Dollond died in 1820, after effecting various improvements in optical and astronomical instruments. He devoted much attention to the mounting of telescopes, and made great improvements in the equatorial stand. He contributed various papers to the Philosophical Transactions.—W. L. M.
DOLMAN. See Parsons, Robert.
DOLOMIEU, Deodat-Guy-Silvain-Tancrède Gratet de, a celebrated French geologist. He was born at Dolomieu, near La Tour-du-Pin, in Dauphiny, on the 24th of June, 1750. He began and ended his scientific career in a prison. When very young he was admitted to the order of Malta. In one of his earliest missions in the service of the order he had a dispute with a brother officer, which ended in his killing him. He returned to Malta and was condemned to death, but his sentence was not carried into effect, and he was imprisoned for life.' In the prison he acquired a taste for physical science. Through the interference of Pope Clement XIII. He was discharged from prison. He fled from Malta, and went to Metz for the purpose of studying the physical sciences. In 1775 he published his first work, "Researches upon the Weight of Bodies at different distances from the Centre of the Earth." He also translated into Italian Cronstadt's Mineralogy, and Bergmann's Observations on Volcanic Substances. For these he was made a corresponding member of the Academy of Paris. This decided his scientific career. He travelled, with his bag on his back and his hammer in his pocket, through Portugal, Spain, Sicily, the Pyrenees, and Calabria, after its visitation by earthquake. During these travels he made important observations on the structure of the earth's surface. He wrote several works on the facts he had collected in his travels. In 1783 he published his "Journey to the Isles of Lipari," and in 1784 his "Memoir on the Earthquake of Calabria." He spent the years 1789 and 1790 in travelling in the neighbourhood of Mont Blanc and Mont Rosa, the valley of the Rhone, Mont St. Gothard, and the range of the Apennines He returned to Paris in 1791, and published several papers as the result of his labours. In 1796 he commenced lecturing on geology and mineralogy in the school of mines of Paris, and gathered around him the most brilliant audiences of the day. In 1798 he was appointed one of the famous scientific staff that was attached to the expedition to Egypt. Unfortunately the vessel in which he was, Le Tonnant, captured the isle of Malta. The smouldering hatred of his order was rekindled by this event, and on his return from Egypt he was shipwrecked off the Gulf of Tarent, and thus falling into the hands of his enemies, was imprisoned and most cruelly treated. Whilst in prison he was forbidden the use of pens and paper, and he wrote his two last scientific works with pieces of burned wood on the margin of his bible. He was rescued from prison by the French government, and returned in triumph to Paris, but too late; his health was shattered. He sought pure air in the mountains of Savoy, where he lingered some weeks and died at Chateauneuf on the 26th of June, 1801. He was the first to describe the rock thereon as the magnesian limestone, and which is familiarly called after him dolomite.—E. L.
DOMAT or DAUMAT, Jean, born at Clermont in Auvergne in 1625, and died at Paris in 1696. Domat was descended by his mother from De Basmaison, a distinguished jurist and antiquarian, known by his Paraphrase sur la coutume d'Auvergne, and a treatise on fiefs and arriére fiefs. His granduncle, Sirmond, who was confessor to Louis XIII., undertook the charge of Domat's education, and brought him to Paris for the purpose. Sirmond was a jesuit, but somehow in his nephew antagonistic feelings were brought strongly into action, and the young advocate—for Domat chose the practice of the bar as his professional occupation—became the intimate friend of Pascal, and the earnest enemy of the jesuits. For thirty years Domat exercised the office of avocat du roi at Clermont. This office was conducted by him with great firmness in times of considerable difficulty. The claims of the noblesse—almost of impunity—while their feuds distracted the kingdom, were fearlessly resisted by Domat, often at the risk of his life, for there was more than one conspiracy to murder him. In 1681 Domat went to reside in Paris, and devote himself to the great work on which his reputation rests—"Les lois civiles dans leur ordre naturel." A pension of two thousand livres was given him. Domat's effort was to teach law as if it were a pure science—an effort which has never perfectly succeeded. The confusion in which the laws—and customs having the force of laws—were through France, led to several attempts to systematize them. Little or nothing was done by the schools of law; and in the seventeenth century the teaching of the schools had ceased to have much effect even in the education of strictly professional students. Whatever was done was effected for the most part by recluse individuals, often unaided, often even discouraged and distrusted. Domat had the jesuits as active enemies. The fact that he was the friend of Pascal, and that, though the father of thirteen children, he did not send any of them for education to the jesuit establishments, was enough to provoke a silent resistance to every effort of an inoffensive man. His work is one of
