122 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



The tube A A may be made either of brass or mahogany 

 of three and a half feet long. The achromatic object-glass 

 of three and a half feet focal distance has an aperture of 

 two inches and three quarters. 



The larger size is with a tube five feet long, and has an 

 achromatic object-glass of three inches and one quarter 

 aperture. 



The eye-tube, as represented by B, contains four eye- 

 glasses, to be used for day or any land objects. There are 

 three eye-tubes, as C, which have two glasses in each, to 

 be used for astronomical purposes. These eye-tubes all 

 screw into the short brass tube at D. By turning the 

 button or milled head at /, this tube is moved out of the 

 larger, so as to adjust the eye-glasses to the proper dis- 

 tance from the object-glass, to render the object distinct to 

 any sight with any of the different eye-tubes. 



The magnifying power of the three and a half feet tele- 

 scope with the eye-tube for land ' objects, is forty-five 

 times, and of the five feet, for land objects, sixty-five times. 

 With those for astronomical purposes, with the three and a 

 half feet, the magnifying powers are eighty, one hundred 

 and thirty, and one hundred and eighty ; and for the five 

 feet, one hundred and ten, one hundred and ninety, and two 

 hundred and fifty times. 



Stained glasses, as g, are applied to all the different eye- 

 tubes, to guard the eye in observing the spots on the sun. 

 These glasses are to be taken off when the eye-tubes are 

 used for other purposes. 



The rack-work is intended to move the telescope in any 

 direction required, and is worked " by means of the two 

 handles at h. When the direction of the tube is required 

 to be considerably altered, the worm screws, which act 

 against the arc and the circle, must be discharged ; then 

 the screw d being loosened, the pin of the rack-work will 

 move easily round in the socket, b. 



For the more readily finding or directing the telescope to 

 any object, particularly astronomical objects, there is a 

 small tube or telescope, called the finder, fixed near the 

 eye-end of the large telescope. At the focus of the object- 

 glass of this finder there are two wires which intersect each 

 other in the axis of the tube, and as the magnifying power 

 is only about six times, the real field of view is very large ; 

 therefore any object will be readily found within it, which 



