424 SUMMARY OF CURRENT RESEARCHES RELATING TO 



suggested with the view of obviating the difficulties found with the 

 ordinary forms in regard to the eye and hand having to be placed in 

 very inconvenient positions. 



The principle of its construction is that neither the pencil itself 

 nor its reflected image is seen, but an image of it formed by convex 

 lenses. With this object the eye-piece of the Microscope in its ordinary 

 position serves at the same time as the eye-piece of a telescope, whose 

 axis is twice bent at a right angle. This is provided with two mirrors, 

 the first of which (0 • 2 mm. thick, and necessarily transparent) is 

 immediately beneath the eye-piece, and the second (which need not 

 be so thin) is over the objective of the telescope. Between the 

 two mirrors is a lens which again erects the inverted image of the 

 pencil. 



By the use of this apparatus the microscopical image is seen 

 direct and without any fatigue to the eye. The drawing hand also 

 lies on the right directly beneath the Microscope and therefore in the 

 most convenient position. 



To avoid the glare of the paper drowning the image of the object, 

 Dr. HoUe recommends — not the more simple process of modifying the 

 light — but that the drawing should be made with a white pencil on 

 a black ground. " In order, however, not to copy what has been 

 already drawn, it is best to take black unglazed paper, blacken it on 

 the reverse side with lead pencil, and lay it on the drawing paper. 

 The marks of a pointed piece of bone can be seen on the unglazed 

 black paper with sufficient clearness to know which lines of the image 

 already exist on the drawing paper and which not." 



Manipulation of the Beck Vertical Illuminator.* — Dr. J. 



Edwards Smith considers that this illuminator is a difficult one for 

 the tyro to use, and that his first attempts will probably result in 

 failure, and whilst it is not easy to give the necessary instruction in 

 writing a few hints may prove of value. 



A dry mount of Podura answers very well for the novice to work 

 upon. Select the widest aperture objective, and examine the object 

 in the ordinary way and get a tolerable correction. Next put on the 

 illuminator, and using transmitted light " hunt through the slide ; 

 among the numerous scales will probably be found one or two which, 

 in order to bring into focus, the objective will require to be withdrawn 

 from the cover slightly. In such a case the chances are that that 

 particular scale is nearer the cover, and if in good condition may be 

 selected for further operations. Next, bring the lamp (a flat-wicked 

 one) towards the observer, revolving the tube of the illuminator so 

 that the lateral aperture shall be in proper position to receive the 

 light from the lamp, the latter being about seven or eight inches 

 distant, and the flame about the same height as the aperture of the 

 illuminator. Now grasp the little knob connected with the interior 

 glass disk and turn it so that light shall be reflected to the rear of the 

 objective ; at the same time, and looking through the tube as you 



* ' How to see with the Micrcscoiie,' 1880, pp. 221-3. 



