CAIilFERS. 45 apart of the points of the legs, we then have a registering calipers. Calipers of this general form are made in a variety of shapes and with a variety of registering and adjusting devices for special purposes. Generally the legs, instead of being straight like the legs of dividers, are cuned CALIPH. FIG. 1. SIMPLE CALIPEBS. so as to converge toward each other at the ex- treme points. Fig. 1 shows a form of calipers for rough measurements such as measuring the di- ameter of rolled rods or the thickness of rolled plates. Fig. 2 shows a form of calipers, known as micrometer calipers, for very precise measure- FIG. 2. MICBOMETES CALIPEES. ments. The mechanical principle embodied in the construction is that of a screw in a fixed nut. An opening to receive the work to be measured is afforded by the backward movement of the screw, and the size of the opening is indicated by the graduations. The pitch of the screw, or distance between its threads, is forty to the inch in this particular calipers, and the graduations on the barrel are forty to the inch and are figured 0, 1, 2, etc., at every fourth division. As these graduations conform to the pitch of the screw, each division equals the longitudinal distance traversed by the screw in one complete revolu- tion, and shows that the calipers has been opened A °^ Tthy "^ '"^^ inch. The beveled edge of the thimble is graduated into twenty-five parts and is figured at every fifth division, 0, 5, 10, 15, 20, etc. Each division when coincident with the FIQ. 3, VEENIEB CALIPEH.S. base-line of the divisions on the barrel indicates that the gauge-screw has made ,'. of a revolution and that the opening of the calipers has increased A of jisTT °r mVi) "^ ""^ inch. Hence to read the calipers multiply the number of divisions visible on the scale of the barrel by 25, and add the number of divisions on the scale of the thimble from zero to the line coincident with the base-line of the graduations on the barrel. For example, as the calipers is set in the illustra- tion, there are three whole divisions visible on the barrel, ilultiplying this number by 25 and adding 5, the number of divisions registered on the scale of the thimble, the result- is yfg^ of an inch. There are also special forms of micrometer calipers for the accurate measurement of V- threads on screws, bolts, etc., and calipers for measuring the depths and thickness of gear-teeth and other purposes. A common form of calipers, known as vernier calipers, is shown by Fig. 3. (See Vernier.) See G.UGES. CA'LIPH (Fr. calif e, Ar. khalifa, successor, from kliahifa, to succeed). The title of Moham- med's successors in temporal and spiritual power, from which the early Empire of Islam is known as the Caliphate. While the first impulse of conquest given to the Arabs by the new faith en- dured, the power of the caliphs was vast, cover- ing the whole world of Islam; but with time the usual consequence followed the combining of spiritual authoritj- with temporal dominion. The caliphate became the subject of factional strife and a prize for ambitious leaders, and rival dy- nasties broke Islam up into independent powers united only in enmity to the vmbeliever. The first four "caliphs (632-061), Abu Bekr, Omar, Othman, and Ali, were generally recognized as true successors to the spiritual authority of the Prophet, all being members of his immediate family, though under Ali, who was assassinated, there were insurrectionary movements. Tli/e Ommiads (661-750) held a more doubtful title, but still one that was recognized. With the ac- cession of the Abbassides the Jlohammedan world was divided, a survivor of the Ommiads found- ing in Spain the emirate (later caliphate) of Cor- dova. This was never a true caliphate according to ilohammedan law, but it was one of the great- est in wealth and civilization of all the Moham- medan empires. The Abbasside dynasty saw other rivals arise, the Aglabites and Edrisites in Africa, as well as minor claimants. It was the story of the feudal world everywhere — emirs seizing sovereign power whenever the oppor- tunity offered. From the Tenth Century on, the Abbasside caliphs were mere creatures of the powerful Turkish guards, rashlv organized by the Caliph Motassem (833-842). In 1258 another Motassem, the last Abbasside caliph, was put to deatli by Hulaku Khan (see Mongol Dynasties; Persia). Nominal successors of the caliphs performed the spiritual functions of the office in Egjpt as late as the Sixteenth Century, when the Turkish sult^Tns reunited the spiritual and temporal headship of Islam in their own persons. There was a Shiite (q.v. ) caliphate instituted in Persia in l.i02. The first four caliphs had their capital at Medina; the fourteen Asiatic Ommiads made Damascus their seat of power; while Bag- dad was that of the thirty-seven Abbassides. There was also established at Cairo in Egypt (1)09-1171) a dissenting caliphate, that of the Fatimites. Twenty-two Ommiads (756-1031 ) of the Spanish line ruled in Cordova. See Abbas- sides; Fati.mites; Ommiads; and .separate arti- cles on the greater caliphs. Consult, also: Sir William Muir, Annals of the Early CalipJuite (London, 1883), and The Caliphate: Its Rise, Decline, and Fall (London, 1891), an abridgment of the Antials, with a continuation to the fall of
