TELESCOPES 19 



the draw-tubes, 4^ inches at the eyepiece end and 3 inches at the object- 

 glass end, the objective would not have been more than 2 inches in 

 diameter. 



The fine and imposing looking eyepiece is, however, complete. It 

 consists of two lenses of 3 inches diam. and 12 inches focal length, and 

 i^ inches diam., 2| inches focal length, mounted about .7^ inches apart 

 in an eyepiece with a draw-tube. 



These Orrery telescopes are of great historic interest as represent- 

 ing the instruments of the time of Flamsteed, who, when he went to 

 Greenwich in 1676, only had two telescopes, one of 15 and the other of 

 7 feet focus, a Townley micrometer, and a small quadrant. None of 

 these instruments are now in existence. Halley found no instrument 

 at Greenwich in 1719. His first acquisition was a 5-foot Hook telescope. 



91. ^-inch Silver Terrestrial Telescope. c. 1700. 



One draw : length opens io| inches, closing to 7! inches. Orrery Coll. 



Both eyepiece and object-glass are fitted with sliding caps. The 

 objective is of 6 inches focus; the four lenses of the erecting eyepiece 

 are mounted in sections of the beautifully made draw-tube which fit 

 together with bayonet joints, engraved for identification with leaves, 

 a ball, and a rose. A small hole is provided to allow the escape of air 

 when the draw-tube is being pushed in. 



The invention of the erecting or terrestrial telescope by the applica- 

 tion of four lenses is thought to have been made by Compani of Rome. 



92. if -inch Refractor, of about 9 feet focal length. c. 1700. 



Orrery Coll. 17. 



Object-glass inscribed Jac: Wilson, Londini fecit, mounted in a wood 

 cell. Painted wooden tube 3 inches square, with sliding copper cradle 

 with trunnions for use on the tripod belonging to the i^-inch refractor 

 described below. Length when closed 6 feet : extension, partly by 

 a square wooden draw-tube, partly by a round green vellum tube, which 

 serves as a fine adjustment 



The eyepiece is unfortunately imperfect, the two lenses nearest the 

 objective being the only parts remaining of an erecting eyepiece. Writ- 

 ings on the square draw-tube at 8 feet 6 inches, 7 feet 6 inches, and 

 6 feet from the object-glass describe marks at those points respectively 

 as 'Mark for the longest objective with 3 eyeglasses obiect erected', 

 ' Mark for the shortest objective with 3 eyeglasses obiect erected', and 

 ' Mark for the objective with one eyeglass obiect inverted '. The eye 

 lens and cap are therefore missing. The metal band round the tube 

 at the eyepiece end once carried a hook for suspension. 



