i66 



Telescope, Gregorian. A reflecting telescope in which the con- 

 cave mirror is pierced with a small central aperture, and a 

 subsidiary, small, concave mirror forms a secondary image 

 which is viewed through the aperture in the large mirror 

 by the aid of an eyepiece. [11, 18.] 



Telescope, Herschellian. A reflecting telescope, designed by Sir 

 Wm. Herschel, in which the axis of the concave mirror is 

 slightly inclined to the incident rays and the image is thus 

 thrown to one side of the axis, and observed directly by 

 means of an eyepiece at the front end of the telescope. [11, 

 18.} 



Telescope, Naval. A refracting signalling telescope, with taper 

 body and having a sliding tube for focussing, in several 

 sizes, ranging in power from 20 to 50. [1, 2, 3, 5, 6, 8, 9, 

 10, 13, 15, 16, 17, 18, 20, 21, 23, 24, 25, 26, 27, 28.] 



Telescope, Newtonian. A reflecting telescope, invented by Sir 

 Isaac Newton, in which the eyepiece views at right angles 

 to the axis the image formed by the main speculum, by means 

 of a speculum (or a totally reflecting prism) set at 45 to 

 the axis close to the focal point. [2, 3, 11, 13, 18, 26.] 



Telescope, Officer of Watch. A regulation, hand, refracting 

 telescope, as used by officers in the Royal Naval Service. 

 Power 15. [2, 3, 5, 9, 13, 15, 16, 17, 20, 21, 23, 24, 25, 26, 

 27, 28.] 



Telescope, Oscillating Prism. 



Telescope, Beading. A small refracting telescope used lor 

 reading at a distance a scale of, for example, a galvano- 

 meter. [1, 2, 3, 10, 13, 15, 17, 19, 21, 26, 27.] 



Telescope, Ship's. Known generally as the Day and Night 

 Telescope (q.v.). [3, 6, 8, 9, 10, 13, 15, 16, 17, 20, 21, 23, 

 24, 26, 28.] 



Telescope, Sighting. A refracting telescope with an index, or 

 graticule, used for sighting guns. [1, 2, 3, 8, 9, 11, 13, 16, 

 17, 18, 20, 21, 22, 23, 25, 26, 27.] 



Telescope, Signal Station. A high power, signalling, refracting 

 telescope, with tripod, as used at signalling stations. [1, 2, 

 3, 8, 9, 13, 15, 17, 18, 20, 21, 22, 23, 25, 26, 27.] 



Telescope, Spotting. A binocular, refracting telescope, giving 

 greatly increased stereoscopic vision for estimating distances. 

 [2, 3, 10, 13, 20, 26, 27.] 



Telescope, Submarine. A special form of refracting telescope, 

 with a large plane object-glass, which is submerged beneath 

 the surface of the water. [13, 15.] 



Telescope, Variable Power. A telescope in which parts of the 

 eyepiece are made to move conformably so as to vary the 

 power continuously while keeping the object in focus. 



Telespectroscope. An instrument, compounded of the telescope 

 and spectroscope, for observing the light from the planets 

 and fixed stars, for ascertaining their physical condition, 

 and the composition of their atmospheres. [11.] 



