702 SUMMARY OF CURRENT RESEARCHES RELATING TO 



diately below. From the object the light is diffusely reflected upwards. 

 Of the reflected rays, only those which are confined in their passage 

 to the space marked off by the dotted lines reach the objective. The 

 cone of rays travelling upwards through the objective meets the erecting 

 mirror and is finally reflected upon the screen. 



When transmitted light is used the mirror previously employed is 

 turned back so as to allow the pencil of rays to pass to a second mirror. 

 From there it is reflected obliquely downwards upon a third mirror, 

 which again reflects it vertically upwards into the condensing lens 

 situated below the object-stage. On leaving the condenser, the rays of 

 light pass through the transparent object and form a reduced image of 

 the search-light reflector near the projection objective. They next pass 

 through the objective and meet the erecting mirror. The latter is fitted 

 with a regulator. The position of the mirror is that required for pro- 

 jecting the picture obliquely upwards. 



Fig. 130 represents the simplified Microscope with a planar lens 

 in use. Fig. 131 shows the whole epidiascope and the simplified Micro- 

 scope attached to it when used with a planar lens. Fig. 132 gives the 

 epidiascope with the simplified Microscope provided with an ordinary 

 microscopical objective and ocular. 



Projection Microscopes using Electric Arc or Oxyhydrogen 

 Light.* — A. H. Cole points out that the utility of projection Microscopes 

 depends upon the degree of success with which three practical problems 

 are solved : — (1) A light of intense brilliancy must be produced and 

 kept in the optical axis ; (2) the system of condensers must collect the 

 largest possible percentage of light rays from the luminous point and 

 deliver them at the proper angle of convergence for each of the objectives 

 used ; (3) the apparatus must not be too cumbersome or complicated, 

 or too expensive for ordinary use. Fig. 133 shows the author's attempt 

 to solve these problems, the body being rotated upwards on the top of 

 the plate and held in position by a slender support so as to give a 

 clear view of the 90° arc lamp and electrical connections. The base- 

 board is cut away under the lanq) so as to permit the use of long vertical 

 carbons. At the rear end and right side of the board is placed the 

 switch in the most convenient position for use. On the opposite side 

 of the board is the fuse-block. At the right of the fuse-block, as seen 

 in the illustration, are two binding-posts connected with the fuse-block 

 by two twisted flexible wire cables. From the other end of the fuse- 

 block two similar cables connect with the binding-posts of the knife- 

 switch. When the electricity is turned into the lamp by closing the 

 switch, it passes to each carbon through the cables connected with the 

 right-hand binding-posts of the switch. The arc is formed between 

 the proximate ends of the carbons, which are shown on an alternating 

 current of 110 volts, and in about the proper adjustment to develop the 

 maximum power of the lamp. The carbons are fed together or singly 

 by turning both feed-wheels at the end of the horizontal shaft below 

 the horizontal carbon at the same time, or either one alone, as needed. 

 The entire lamp may be elevated, or lowered, and rotated to the right 

 or left, and moved along the base-rods and clamped in any position. 



* Journ. App. Micr., v. (1902) pp. 1892-3, 2012-3 (1 fig.). 



