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IV. — Descrijition of a New Form of Camera Lucida. 

 By J. Cunningham Russell, M.D., Lancaster. 



{Read 11th December, 1878.) 



The principle of this instrument is that, in place of the paper or 

 its reflection heing viewed by the eye directly as in the cameras 

 hitherto constructed, there is formed, by means of a lens acting as 

 the object-glass of a telescope, a real image of the paper at the 

 same point as the image of the object formed by the microscopic 

 objective, and these two images forming one combined image are 

 viewed through the eye-glass of the Microscope. The advantages 

 of this construction are that the images being as one it is impossible 

 that the image of the object should shift even in the least degree 

 upon that of the paper, and that the images being at exactly the 

 same distance from the eye, they are both in focus at once, and there 

 is no straining of the eye to accommodate it to both object and paper, 

 as is apt to occur with other instruments. It also avoids the 

 necessity of looking through a small aperture, the ordinary eye- 



Fm. 2. 



Fig. ]. 



a. Tube filtiii}; into the Micro- 

 scope. 



&, Rectangular reflecting 

 prism. 



c. Horizontal tubes. 



rf, Vertical tub? (inclined when 

 in use), containing 



e, Eye-piece. 



j'. Plane reflector of tinted 

 glass, and 



fir. Telescopic object-gla.ss. 



ti, Krecting prism attached to 

 the last. 



piece being used ; and it admits of a convenient inclination being 

 given to the eye-piece while the body of the Microscope is upright. 

 The construction of this instrument is shown in the accom- 

 panying figures and is as follows : — A tube fits into the tube of 



