BURNEY

Chables, second son of the historian of music, a cla ical scholar and critic of high reputation. He was bom at Lynn, in Norfolk, in 1757, and received his education at the Charter house School, and the Universities of Cambridge and Aberdeen; distinguished himself as a writer in the Monthly Review, to which he contributed many articles on cla ical literature; subsequently entered into holy orders, and obtained some preferment the church. He died in December, 1817, and his valuable collection of books, many of them enriched with manuscript notes, was purchased by Parliament for the British Museum. Bumey published an Appendix to Scapula's Greek Lexicon from the MSS. Dr. Askew; a valuable edition of the Choral Odes.^Elschylus, the Greek tragedian; the Greek Lexicon of Philemon; Remarks on the Greek Verses of Milton; an Abridgment of Pearson's Exposition of the Creed; and a sermon preached at St. Paul's: besides which he printed, for private distribution, a small impre ion of the Latin epistles of Dr. Bentley and other learned scholars. BURNING-GLASS, a lens which unites the rays of li^t that fall upon it in so narrow a space as cause them to kindle any combustible matter coming in their way, like fire. The same name has been sometimes given, though improperly, to the burning mirror. The lenses commonly used as bumiu<;a gla es are convex on both sides; these bring the rays upon a point with the greatest force, because of the shortne of their focal distance. The effects of a burning-gla are more powerful in proportion as its surface is greater, and its focus smaller. That such a gla may produce its greatest effect, it is nece ary that the rays of the sun should fall upon it in a perpendicular direction, which is the case when the image of the sun, that appears at the moment of burning, is circular. If a second lens, of a smaller focal diiftance, is placed between the first and its focus, so as to intercept the rays which pa through the first, they are still more condensed, and united in a still narrower compa , so that the effect is greatly augmented. The Greeks and Romans seem to have b^n acquainted with burning-gla es, or at least with a kind of transparent stones similar to them. They became more known in the thirteenth century. At the close of the seventeenth, Von Tschirnhausen caused immense burning-gla es, consisting of one piece, to be polished vn& incredible pains. Two of them, still in Paris, are 33 inches in diameter, and the weight of one amounts to 1 60 pounds. Both gla es produce an effect equal to that of tiie most intense fire. They kindle wood which is both hard and wet in a moment, and make cold water, in small ve els, boil in an instant; metals, placed upon a plate of china, are melted and vitrified by them; tiles, slates, and similar objects, become instantly red-hot and vitrified. But these have been surpa ed by one of made of flint-gbi by Mr. Parker of London. It a has a diameter of 3 feet, a focal distance of 6 feet 8 inches, is 3J inches thick at the centre, and weighs 212 Ibe. The effects of this lens are still more extraordinary than those of Tschimhausen's gla es. A much dieaper method of making burning-gla es was adopted by Bri on and Lavoisier in 1774, who put together two lenses, resembling those used for watch gla es, filling up the space between them with a transparent fluicL In this manner veins and impurities may be more effectually avoided. They succeeded in making a burning-gla of 4 feet in diameter, the greatest thickne of which, in the centre, amoimted to 8 inches, and which, of itself, had a much greater power than the gla es of Tschirnhausen in conn^^tion with a smaller lens or collective gla ; but produced an extraordinary effect if joined to a collective gla . The experiments made by means of large burning gla es are important in chemistry and physics. The power of a burning-gla , however, is tJmost four times le than that of a burning mirror, or reflector (which see) of equal extent and equal curvature. This reflects more heat than the glo allows to pa through it; has a smaller focal dist4mce, and is freo in from the di ipation of the rays which takes place in the burning-gla , since it reflects them all nearly to one point, while the burning-gla refracts them to diff prent points. On the other hand, the burning-gla is much more convenient, on aocotmt of the place of its focus, which is behind the gla . The burning of of point (focus) is an image of the sun; its diameter is equal to the 108th part of the focal distance, and its centre is the foctu properly so called. In the higher branches of geometry and conic sections the fact are points in the parabola, ellipsis, and hyperboL^ where the rays reflected from all parts of these curves meet. Several accidents in modem times have shown that conflagrations may be caused by convex window gla es or water-bottles, , which have the form of to burning-gla es, if the rays of the sun are concentrated by them upon combustible substances lying within their reach. Since the casting and polishing of large lenses arc attended with great difficulties, Buffon^s plan of casting them in pieces or zones, and afterwards putting them together, is commonly practised. Lenses of this last kind are now generally applied augmenting the light on lighthouses, according arrangements introduced by Fresnel, Thomas venson, . (See Lighthouses.) For the history of burning instruments, see the article Burning MiRKORS. 487