114 C. A. Steinheil Sohne, Mtinchen. 



B. Terrestrial Oculars. 



B D Four plano-convex lenses; images 'formed before the first 

 and between the third and fourth lenses; apparent- angle about 44. 



Reading Telescope 



for magnetic observations, without steel or iron; brass tube: ocular 

 supports with rack and pinion adjustment; made to focus distances 

 varying from infinity to about 4 times the focal length. 



Mounted on metal tripod, swinging 30 in either direction on hori- 

 zontal axis; micrometer adjustment in azimuth with clamps and scale carrier. 



All oculars are fitted with cross lines, the lowest power with 

 adjustable diaphragm. 



New Shortened Telescope with Negative System. 



Fig. 23. 



The cone of light emerging from the short focus objective is intercepted 

 by a negative system whereby the "equivalent focal length of the objective be- 

 comes considerably larger than the length of the entire telescope. High mag- 

 nifications may thus be obtained with low power oculars and relatively small 

 dimensions. Magnification and the length of the entire telescope depend upon 

 the distance between the objective and the negative lens of certain focal 

 length; both decrease as this distance is increased. 



The objective, which has a brightness of f/4 and perfectly sharp defini- 

 tion, consists of a biconcave crown glass lens cemented between two flint glass 

 menisci and has been computed together with the concave system as a cement- 

 ed system consisting of a positive flint glass meniscus and a high biconcave 

 crown glass lens. (vid. Dr. Rud. Steinheil's paper in the ,,Zeitsclirift fur 

 Instrumentenkunde" , 1892, November.) 



Tube 



of brass, with tubular stand, in polished sycamore case, portable and 

 of elegant appearance. 



Mounted horizontally and parallactically and balanced upon cast 

 iron tripod and tubular brass pillar for standing in height of table: 

 tripod with screws for placing the pillar vertical. Vertical pillar may 

 be lengthened for astronomical observations. It may be fitted with 

 divided searching circles reading to 5 angular minutes and 20 time 

 seconds. 



The achromatic double objective of the tube has an aperture of 

 61 millimeter (27'") and 73 centimeter (27") focus. The four oculars 

 give the following magnifications: the terrestrial ocular 34, the astro- 

 nomical oculars 36, 81, 108. Ocular arranged for combination with 



