114 On a New Suh-stage for the Microscope, 



quickly applied or removed, and if it could be so placed as to give 

 the best effect in association with the Wenham prism. I also 

 wished to retain the advantage of the Brooks' nose-piece, without 

 any tiresome screwing and unscrewing every time the analyzer had 

 to be used. I managed the matter in this way. The short tube 

 which attaches the nose-piece to the body is just long enough to 

 hold the tube which carries the analyzing prism, and allows the 

 latter to be slipped in close up to the Wenham prism, and rotated 

 by a slightly projecting milled collar. Eoom for this collar is at 

 once obtained by filing down that of the nose-piece attachment. 

 When the analyzer is not wanted, it can be easily drawn out and 

 replaced by a plain tube for ordinary work. The object-glasses are 

 now as near to the Wenham prism with the analyzer on as without 

 it ; and the fields for both eyes can be completely illuminated either 

 with common or with polarized light. The definition too is good ; 

 but, if the operator desires, he can still place the analyzer by means 

 of a simple fitting above the eye-piece as usual, sacrificing, of 

 course, the binocular view. This, however, is a change which he 

 will not often care to resort to when the definition is so good 

 without it. For full illumination, it is sometimes well to interpose 

 the stand-condenser between the light and the mirror, so as to 

 obtain a straight strong beam. It should also be remembered, 

 that with any power higher than a 1-inch, it is desirable to employ 

 the upper stage in combination with the Webster condenser. This 

 illuminates the field for both eyes equally. By the above arrange- 

 ment I can use the polarizing apparatus hinocularly with every 

 power from a 4-inch up to a |^-inch, and obtain in each case a 

 thoroughly satisfactory result. 



For white-cloud illuminator, in conjunction with the stand- 

 condenser placed so as to concentrate the light upon it, I use a 

 hollow disk of roughened porcelain, attached by a pivot to the 

 margin of the ordinary mirror, and capable of being turned aside 

 when not wanted. 



For diffused light I simply grind upon a slab of sandstone owe 

 side of the glass chimney of the lamp. This side can readily be 

 turned towards the mirror when desirable. 



Lastly, permit me to direct attention to the convenience of the 

 Morris' object-holder for showing with low powers the iridescence 

 upon an insect's wings, and other points of interest requiring a 

 certain slope to reveal them, and which cannot always be displayed 

 in the mounting. But if the ball-and-socket joint be made a little 

 larger, it can be perforated so as to allow of transparent illumina- 

 tion, while the steadiness of the holder is increased. For the prac- 

 tical carrying out of the preceding improvements I am much 

 indebted to the intelligent co-operation of Mr, Selby, of the firm 



