Heliostat

a mirror provided with a clockwork motion, so adjusted as to make it follow the course of the sun, which, therefore, till the day departs, continues to be reflected from its face. Also an instrument invented by Gau , in 1821, by means of which the rays of the sun can be flashed to great distances. It consists of an adjustable mirror or reflector, worked in connection with a combination of telescopes, and is now used in all trigonometrical surveys. | aid, triangles, with sides over 100 miles in length, can be measured. ‘Heliotrope, a genus of flowering plants of the: natural order Boraginee.. The Peruvian heliotrope, a shrub with oblong-Jan ceo late wrinkled leaves and small lilac-blue flowers, is in almost universal cultivation for its fragrance. Many beautiful varieties of this species are cultivated in gardens. The common heliotrope is an annual with-small white, or rarely pale red, flowers. Large quantities of the flowers are used by perfumers for making scents. _Heliotrope, or Bloodstone, a variety of chalcedony or of jasper, of a green color with red spots. The finest heliotropes consist of chalcedony, and are translucent, at least at the edges; the jasper bloodstones are opaque. It was much used in the early ages of the Christian Church for the engraving of sacred subjects, the figures being so managed that the red. spots should represent drops of blood.: Heliotype, in photography, a method of transferring pictures from negatives to a hardened gelatin film from which impre ions are made in the same way as from a lithographic stone, Helium, in chemistry, an element first discovered in the sun by means of the spectroscope, and so named because it was supposed to be peculiar to that body. It has since, however, - been chemically discovered on the earth with argon.