ASTRONOMY. 57 



form of a cone, which revolves on strong iron rollers running on a 

 cylindrical iron rail. 



Instruments. The instrumental equipment consists of an Equa- 

 torial Telescope, a Transit Instrument, an Alt-Azimuth Instrument, a 

 Transit Theodolite, a Sextant, a Sidereal Clod', and a Solar Clod: 



The Telescope is a refractor of 4^ inches aperture and a focal 

 length of 64 inches, made by Henry Fitz, of New York. It is 

 mounted equatorially, and is furnished with a Finder of 1 inch 

 aperture, and with Eyc-jrieces varying in power from 30 to 240, re- 

 flecting prism, and sun-shades. The declination and hour circles 

 read respectively to two minutes of arc and four minutes of time. 

 A sidereal motion is given to the Telescope by means of an endless 

 screw attached to the hour circle and moved by hand. 



The Transit Instrument was made by Brunner, of Paris. It has 

 an aperture of 2-^ inches and a focal length of 23 inches. The cir- 

 cle is 10-i inches in diameter, and is graduated on silver to five min- 

 utes, and reads by two verniers and microscopes to three seconds. 

 This instrument has five vertical wires and one horizontal, and these 

 are illuminated in two ways one through the axis, and the other at 

 the object-glass. The eye-piece is so arranged that it may be made 

 either direct or prismatic. There are two spirit-levels belonging to 

 this instrument one attached to the circle, the other a striding level 

 to be used on the axis. 



The Alt-azimuth Instrument was made by E. & G. W. Blunt, of 

 New Y'ork. It has an aperture of 2^ inches and a focal length of 22 

 inches. The circles are 12 inches in diameter, and are graduated on 

 silver to ten minutes. The horizontal circle has four verniers with 

 microscopes, and the vertical circle three ; and each reads to ten sec- 

 onds. It has both direct and reflecting eye-pieces and a collimating 

 eye-piece. The system of wires and the arrangement of the levels 

 are the same as in the Transit Instrument. The wires are illuminated 

 by a lamp placed at one end of the axis. 



The Transit Theodolite was made by Gregg & Rupp, of New 

 York. It has an aperture of 1^ inches and a focal length of 18 inches. 

 The horizontal circle is 101 inch in diameter, and reads by two 

 verniers and microscopes to half a minute. The vertical circle 

 is 8 inches in diameter, and reads by a single vernier and micro- 

 scope to one minute. The magnetic needle carries a vernier at each 

 end, by means of which the arc of the compass-box can be read to 

 single, minutes. This instrument has two wires, and these are il- 

 luminated in the same way as in the Alt-azimuth Instrument. There 

 is a strong portable tripod on which the instrument can be mounted 

 for field-work. 



The Sextant was made by E. & G. W. Blunt. The arc is graduated 

 on silver, and reads by a vernier and microscope to ten seconds. 



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