ADJUNCTS TO THE MICROSCOPE. 47 



inch object-glasses). This is performed by two reflections. 

 The rays from a lamp, rendered parallel by a condensing lens, 

 are received on an elliptic reflector, the end of which is cut off 

 a little beyond the focus, as in Wenham's illuminator for 

 oblique light ; the rays of light converging from this surface 

 are reflected down on the object by a plain mirror attached to 

 the object-glass, and on a level with the outer surface. By 

 these means the structure of the scale of the podura, and the 

 different characters of the inner and outer surface, are rendered 

 distinctly visible." I have not had an opportunity of testing 

 this plan, but have little doubt of its success. 



Camera Lucida. By which drawings are made from the 

 microscope. This is generally formed by placing a small prism 

 of glass, inclined at the proper angle, in front of the eye-piece. 

 In Fig. 17, a, represents the camera, formed of highly-polished 



Fig. 17. 



steel, smaller than the pupil of the eye, inclined at an angle 

 of 45, and fixed to a clip, b, which embraces the eye-piece. 



Frog-plate; Fig. 18; on which frogs or fish are tied to ex- 

 amine the circulation of blood in their vessels. The frog, &c., 

 must first be enclosed in a bag, and fastened on the plate by 

 the holes in either side of it. Then thread is tied to about 



