Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . ngular, semicircular, or circular shape, andare made of jiaper, ivory, horn, or metal. a is the ivory or boxwood protractor usually em-braced in a case of mathematical instruments. It isabout sLx inches in length ; the ends and one sideare beveled, and are graduated from 0° to 180. Itsface has one or more diagonal scales for setting offdistances. 6 is a semicirc
Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . ngular, semicircular, or circular shape, andare made of jiaper, ivory, horn, or metal. a is the ivory or boxwood protractor usually em-braced in a case of mathematical instruments. It isabout sLx inches in length ; the ends and one sideare beveled, and are graduated from 0° to 180. Itsface has one or more diagonal scales for setting offdistances. 6 is a semicircular protractor of transparent is a very useful instrument in some cases, en-abling tlie draftsman to see the surface of the paperbeneath. c. A metallic bevel protractor. d is a circular metallic protractor. Each end of the arm e f ! provided with a vernier, readingusually to minutes, and carries a light frame//, having a but-ton on its upper and a finely pointed pin on its lower side;these frames have sufficient spring to keep the pins clear of thepaper as the arm is turned on its axis. The center of the in-strument and the two pins lie in the same straight line, the Fig. 3981. Protracthig-Be vel. They are either. Circidai Pratrartar. former being usually indicated by the intersection of two finecross-lines engraved on a plate of ti-ansparent material in theopening ir; A is an arm provided witii a vernier and carrying, I a set-screw by which the arm may be clamped to the circle Pro-tective Paper. Paper made to prevent i while a slightmoveincnt is imparted to it by means of the tin-tampering with the printing or writing |iientlv gent-screw i. The graduations may extend from 0 to 18(i each ...,f 1,...^.. if \ .... (? ,. ™ 1 * t- wav, may be continued round thecircle from 0° to 36(1^ or both put ipouit A i^.eans preventing or leterting ,,,,„|„„,/„, „„,. ^^t„.;,„ ,„ t,,^ „,,l„.r, „„y be Water-marks are made m ]
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