The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . , containing a trans-lation of the various accounts of Heliogabalus in Greek and Latinauthors, notes, bibliography and illustrations; O. F. Butlsr, Studiesin the Life of Heliogabalus (New York, 1908); Gibbon, Decline andFall, ch. 6; H. Schiller, Ceschichte der rdmischen Kaiserteit, ii. (1883). p. 759 ff. On the Syrian god see F. Cumont in Pauly-Wissowas Realencyclopadie, v. pt. ii. (1905). HELIOGRAPH (from Gr. riKvoi, sun, and ypli4>tu> to write),an instrument for reflecting the rays o
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . , containing a trans-lation of the various accounts of Heliogabalus in Greek and Latinauthors, notes, bibliography and illustrations; O. F. Butlsr, Studiesin the Life of Heliogabalus (New York, 1908); Gibbon, Decline andFall, ch. 6; H. Schiller, Ceschichte der rdmischen Kaiserteit, ii. (1883). p. 759 ff. On the Syrian god see F. Cumont in Pauly-Wissowas Realencyclopadie, v. pt. ii. (1905). HELIOGRAPH (from Gr. riKvoi, sun, and ypli4>tu> to write),an instrument for reflecting the rays of the sun (or the lightobtained from any other source) over a considerable main application is in military signalling (see Signal). Asimilar instrument b the heliotrope, used principally for definingdistant points in geodetic surveys, such as in the triangulationof India, and in the verification of the African arc of the is necessary to distinguish the method of signalUng termedheliography from the photographic process of the same name(see Photography). 224 HELIOMETER. Fig. 3. HELIOMETER (from Gr. fi\io5, sun, and ykrpov, a measure),an instrument originally designed for measuring the variationof the suns diameter at diSerent seasons of the year, but appliednow to the modern form of the instrument which is capable ofmuch wider use. The present article also deals with otherforms of double-image micrometer. The discovery of the method of making measures by doubleimages is stated to have been first suggested by O. Roemer about1768. But no such suggestion occurs m the Basis Astronomiae ofPeter Horrebow (Copenhagen, 1735), which contains the only works „, of Roemer that re- main to us. It wouldappear that to Ser-vington Savary is duethe first invention ofa micrometer formeasurement bydouble image. Hisheliometer (describedin a paper communi-cated to the RoyalSociety in 1743, andprinted, along witha letter from JamesShort, in Phil. Trans., 1753, p. 156) was
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