112 Modern Microscopy 



touch the bearings in which the tube of the microscope is 

 raised and lowered. It is well to have the lever of the iris 

 diaphragm working in front of the body, and so that this 

 may be easily arranged the male thread should be so 

 mounted that it may be rotated, but should be very stiff in 

 its rotary movement. 



Camera Lucida. 



This is designed to assist in drawing objects seen in the 

 microscope. Photo-micrography has to a large extent 

 superseded it ; still, there are a great many who prefer this 

 method to any other. Dr. Beale's neutral-tint reflector, 

 which is supplied by all the opticians, is the cheapest and 

 a very good form. It consists essentially of a neutral-tint 

 glass — in which the image of the object is reflected — 

 mounted in a frame to fit over the eyepiece. The method of 

 using it is as follows : The microscope is set in a horizontal 

 position, with the centre of the eyepiece 10 inches from the 

 table. Illumination is arranged in the ordinary way. The 

 cap of the eyepiece is removed, and the neutral-tint reflector 

 is fitted in place of it, and is so arranged that the centres of 

 the neutral-tint glass and the eye-lens of the eyepiece are in 

 alignment, the former being set at an angle of 45°. On , 

 looking on this neutral-tint glass from the upper side, a 

 disc of bright light will be seen on it, and if a piece of white 

 paper be spread below on the table, on further examination 

 the outlines of the object will appear to be upon the paper. 

 If a pencil be now taken, the specimen can be sketched in 

 its magnified form. This will be found somewhat difficult 

 at first, nearly every worker seeming to find it necessary to 

 work in some special manner of his own ; but the secret of 

 success is to arrange the balance of illumination by turning 

 the lamp-wick up and down until a degree of light is found 

 at which the pencil-point and image can be distinctly seen. 

 When using students' microscopes, the eyepieces of which 

 have no caps, it is usual to remove the eyepiece, fit the 

 tube of the reflector to the outside of the top of the 



