telerpeton

[Gr. tēle =far off, and her pet on a reptile, a creeping thing; herpo to creep.] Palæont.: A genus of Lacer til i a, founded the image is formed by refraction through an object, gla , in the latter by means of a concave mirror or speculum. A refracting telescope in the simplest form consists of a double convex lens (the object-gla ), and a second and smaller lens, also doubly convex (called the eyepiece). To render a telescope achromatic, the object-gla is made double or triple, and the eyepiece is generally com posed of two lenses adapted to each other. Not only does a telescope magnify objects, but it collects and concentrates upon the eye a greater amount of light than would enter the organ if una isted, and the larger the object-gla the greater in both respects is the power of the telescope; and a friendly rivalry exists between civilized nations as to which shall po e the most powerful telescope. One constructed by Mr. Howard Grubb of Dublin for the Vienna Observatory has an object-gla two feet three inches in diameter, and one made by Mr. Alvan Clark of Boston, Ma ., for the Ru ian astronomers, is two feet six inches. The obstacle to further progre arises from the difficulty of forming a large disc of optical gla pure enough and uniform enough to be suitable for telescopes. This is the reason why reflecting telescopes have come into us use. Lord Ro e's great reflecting telescope has a reflector of six feet in diameter, and can magnify an object 407 times without rendering it le bright than it appears to the naked eye. These large telescopes are for astronomical purposes. [EQUATORIAL, MERIDIAN CIRCLE.] A refracting, astronomical telescope, having the eyepiece of a single lens, or of a pair of lenses, does not reverse the image formed by the object-gla , and therefore exhibits objects inverted, which does not much matter in astronomical obser vation. A terrestrial telescope, for looking at objects on the earth, has an eyepiece with two more lenses than an astronomical one; it therefore inverts the image and exhibits objects erect. All good telescopes are now Achromatic. [ACHROMATIC-TELESCOPE.] The Yerkes Telescope, the gift of Mr. Charles T. Yerkes to the University of Chicago, is one of the largest refracting telescopes in the world. The column and head, of cast-iron, rise to a height of 43 tonschein diameter feet long, and weighs 312 feet, and weigh 50 tons. The polar axis, of steel, is inches in diameter feet long, and steeighs 12 15 11% Mantell on remains of a reptile which he called Telerpeton elginense, discovered in 1851 by Mr. Patrick Duff, in light-colored sandstone, once referred by some geologists to the Upper Devonian, but now held to be Tria ic. The dentition seems to have been acrodont, and it differed from most existing lizards merely in having amphicœlous vertebræ. (Quar. Jour. Geol . Soc ., viii. 100.)