The _Spectroscope_ is an instrument by which the colours of the solar rays are separated and viewed, as well as those of other incandescent bodies. By it, not only the elements of the heavenly bodies have been determined, but remarkable results have been had in analysing well-known metals and discovering new ones. Its powers and its principles have been so developed during the century by the discoveries, inventions and investigations of Herschel, Wollaston, Fraunhofer, Bronsen and Kirchoff, Steinheil, Tyndall, Huggins, Draper and others, that spectrum analysis has grown from the separation of light into its colours by the prism of Newton, to what Dr. Huggins has aptly termed “a new sense.” We have further referred to this wonderful discovery in the Chapter on Chemistry. The inventions and improvements in optical instruments gave rise to great advances in the making of lenses, based on scientific principles, and not resting alone on hard work and experience. Alvan Clark a son of America, and Prof. Ernst Abbe of Germany, have within the last third of the century produced a revolution in the manufacture of lenses, and thereby extended the realms of knowledge to new worlds of matter in the heavens and on earth. _Solarmeter._--In 1895 a United States patent was granted to Mr. Bechler for an instrument called a solarmeter. It is designed for taking observations of heavenly bodies and recording mechanically the parts of the astronomical triangle used in navigation and like work. Its chief purpose is to determine the position of the compass error of a ship at sea independently of the visibility of the sea horizon. If the horizon is clouded, and the sun or a known star is visible, a ship’s position can still be determined by the solarmeter. _Instruments for Measuring the Position and Distances of Unseen Objects._--Some of the latest of such instruments will enable one to see and shoot at an object around a corner, or at least out of sight. Thus a United States patent was granted to Fiske in 1889, wherein it is set forth that by stationing observers at points distant from a gun, which points are at the extremities of a known base line, and which command a view of the area within the range of the gun, the observers discover the position and range of the object by triangulation and set certain pointers. By means of electrical connection between those pointers and pointers at the gun station based on the system of the Wheatstone bridge, the latter pointers, or the guns themselves serving as pointers, may be placed in position to indicate the line of fire. By a nice arrangement of mirror and lenses attached to a firearm the same object may be accomplished. Similar apparatuses in which the reflectory surfaces of mirrors mounted on an elevated frame-work, and known as _Polemoscopes_ and _Altiscopes_ and _Range-Finders_, have also been invented, and used with artillery. But such devices may be profitably used for more peaceful and amusing purposes.