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Knight's Mechanical Encyclopedia (ed. Knight), M. (search)
provided with the compass, quadrants, sea-charts, and other instruments, equal to the Portuguese. We do not wonder, for the China seas had been navigated by their aid over 1,000 years when the brave navigator repeated the feat of the mariners of Pharaoh Necho, about 610 B. C. The gimbal-joint and compass-box were invented by the Rev. William Barlowe in 1608. The dip of the needle was discovered by Robert Norman of London, 1576; the diurnal variation, by Graham, a London watchmaker, in 1722. An azimuth compass is one used at sea for finding the horizonal distance of the sun or a star from the magnetic meridian. Lord Caithness has substituted for the gimbals a pendulum and a ball; the latter working in a socket in the center of the bottom of the compass-bowl. Albini's self-registering compass is an instrument by which a continuous record is kept of the course steered by the vessel on board which the compass is placed. The compass-card carries on its under side, and nea
Knight's Mechanical Encyclopedia (ed. Knight), P. (search)
ersennus ( Harmonicorum, Paris, 1636) it had 49 strings, of which the lower 30 were made of latten (flat brass wire) and the remainder (19) of steel or iron. The note depended on the size of string and tension, there being one note for each string, and but 5 or 6 sizes of strings. The spinet was always triangular, and had the wires carried over a bent bridge; the strings of the virginal usually went direct to the screw-pegs. The illustration is from Bonanni's Gabinetto Armonico, 4to, Rome, 1722. r is the harpsichord, which is, in fact, a largesized spinet, but it differed from the latter and from the virginal in having two strings to a note. The illustration is from the work of Mersennus just quoted. The action of the harpsichord was simply a key and what is called a jack, which is a piece of pear-tree with a small movable tongue of holly, through which a cutting of crow-quill was passed to touch the string when the jack was in action. （Burney.) Thus the mechanism of the jack was
Knight's Mechanical Encyclopedia (ed. Knight), S. (search)
el ones for the upper. It was used in France as early as A. D. 1515. The illustration q, Plate XL. page 1692, is from Bonanni's Gabinetto Armonico, 4to, Rome, 1722. The spinet was always triangular, and occupied a place in point of time between the virginal and the harpsichord. Unlike the former, its strings were strained ovose trunnions are placed in a carrier, which is pivoted in a socket, so that by the two adjustments the gun may be pointed in any direction. A pivotgun. See page 1722. 3. (Nautical.) A rest, having adjustment in azimuth, for supporting a small piece of ordnance on the gunwale of a boat or vessel. 4. (Saddlery.) A loop izontal plane. See swing-bridge; pivot-bridge. Swiv′el-gun. （Ordnance.) One mounted on a pivot to traverse horizontally in a circle. See pivot-gun, page 1722. Swiv′el-hang′er. A form of shaft-hanger invented by Edward Bancroft, R. I., in which, to ensure the weight of the shaft being received over the entire leng
Knight's Mechanical Encyclopedia (ed. Knight), U. (search)
ic variation. Variation or declination is the horizontal angle which a needle makes with the meridian. The changes of declination are of three kinds. 1. Secular. That which takes place in cycles. At London, in 1550, the variation was 11° 17 E; about 1660 it was 0°. It then began to deviate to the west till it attained its maximum in 1815, 24° 17′ 18″. In 1865 it was 20° 38. 2. Annual. This was first remarked at Paris by Cassini. 3. Diurnal. First remarked at London, by Graham, 1722. The changes are greatest in summer, least in winter. The needle declines toward the west from 8 A. M. till 2 P. M., and then to the east till 8 or 9 P. M. See magnetometer. The variation of the compass was known to the Chinese philosopher, Keon-tsoung-chi, in the twelfth century. He determined it to be from 2° to 2° 30 at Pekin. The French savans who formed part of the plundering host at Pekin a few years since, found time, after participating in the scramble for toot, to test the