242 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



white stripe to one stripe of fig. 48. Thus all the stripes correspond- 

 ing to one colour of fig. 48 are exposed, say the yellow (fig. 49). A 

 half-tone negative is made of this, and during the exposure the most 

 important step occurs : the negative plate is moved continuously until 

 the image which occupied the one-third of the plate occupies the entire 

 surface (fig. 50). This is essential, as in order to ohtain the proper 

 colours the prints must be superposed, and not juxtaposed as in the 

 original positive. The screen is now shifted the width of one line, 

 covering up the image of which a printing plate has been made, and 

 exposing a new image, say the red one. A plate is made of this one, 

 and the operation repeated for the third image, theblue one. A set of 

 photographs of a tiger are given to illustrate the different stages of the 

 process. The final result is very lifelike. 



Dennis' High-power Photomicrography.* — Fig. 51 shows D. W. 

 Dennis' arrangement of the 1899 Zeiss apparatus, which was placed on 



an unshakable stone floor, and consisted of two tables supported on 

 adjustable metal legs, the combined length being 10^ feet. One table, 

 4 ft. long, carries the arc light and illuminating accessories ; the 

 other carries the Microscope and camera. The objectives are apo- 

 chromatic, from 70 mm. to 2 mm., with compensating and projecting 

 eye-pieces. The fine adjustment screw is controlled by a brass rod, 

 which lies on the bench under the camera, and has a pulley and cord 

 attachment A, with the milled head of the micrometer screw. The 

 Microscope is so supported by an adjustable brass pillar B, that this 

 pulley cannot in the least affect it. The camera is carried on two 

 nickeled steel tubes C, which rest on adjustable metal supports, and 

 the board D, on which the Microscope rests, is bound also by clamps to 

 these same tubes. Four strong adjustable pillars E hold the board 

 firmly at one distance from the table. The total effect of these arrange- 

 ments is to make the Microscope and its supports immovable. 



* Journ. App. Micr., Nov. 1901, pp. 1525-7 (3 figs.). 



