Heliogabalus ,.See Elagabalus.
Heliometer , (Gr. the sun, and measure), an instrument to measure the diameter of the sun, or other small arc in the heavens. Several instruments receive this name, but it is now usually applied to a telescope whose object glass is divided into two parts, capable of sliding by each other, so that they may be directed to opposite edges of the sun. Two images of it are thus formed, tangent to each other, and the displacement of the parts of the object glass measures the diameter of the sun.
Helioscope ,.See Telescope.
Heliostat , and Heliotrope, instruments used by surveyors for rendering distant stations visible. The heliostat was invented by's Grave-sande about 150 years ago, and consists of a mirror turned by clockwork in the pathway of the sun, in such a manner that it will reflect his rays in a certain direction. A mirror of only one inch diameter can be seen eight miles, and appears as a brilliant star at a distance of two miles. The heliotrope is simply a mirror fixed permanently at a station so as to throw its rays to another station, or always in one direction. This requires of course that an observation should be taken at a certain moment, as the direction of the reflected beam is constantly changing. For most observations the latter instrument answers all the purposes of the former, and is much less expensive.
Helix , (Gr. a whorl or coil), in architecture, a spiral winding around a central axis, according to some authorities without approaching it, in which case it would be designated a spiral. The little volutes under the flowers of the Corinthian capital are also called helices. - In electro-magnetism, a helix is a coil of wire wound around any body which is to be magnetized by the passage of the electric current through the wire. The power is increased with the number of turns, the wire being insulated, so as to prevent lateral discharge, by winding cotton thread about it.
Helix , in conchology. See Snail.
Hellas ,.See Greece.
Helle , in Greek legends, a daughter of Athamas, king of Thebes, by the goddess Ne-phele. When her brother Phrixus was about to be sacrificed, the mother rescued him, and placing the two children on the back of the ram with the golden fleece, which she had received from Mercury, fled with them to Asia; but between Sigeum and the Chersonesus Helle fell into the sea, and thenceforward that part of it was called Hellespontus, the sea of Helle.
Hellen ,.See Greece, vol. viii., p. 187.