ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



241 



early telophase of mitosis ia Ascaris megalocephala var. bhalens • the 

 polar bodies and the egg-cell wall are seeu ; the centrosome is divided 

 j list below the polar bodies. 



A Notable Advance in Colour Photography.*— "It is now possible 

 for a newspaper correspondent in China to take snap-shots in his 

 ordmary camera, fitted with a newly perfected screen, to send the 

 negative to New York, and there have the picture reproduced in all its 

 original colours, the printer having no previous knowledge of the 

 colours themselves." 



The preceding quotation is Messrs. Brasseur and Sampolo's own 

 description of their new process in three-colour work. But, in contra- 

 distinction to the older methods, only one negative is required, and the 

 exposure is not more than one-tenth to one-sixtieth of a second. All 

 makes of polychrome screens can be used to obtain the negatives, but 





Fig. 48. 



Enlarged 53 times. 

 Positive on glass made 

 from original negative ; 

 successive groups of 

 coloured lines, each 

 colour repeated every 

 third line. 





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Fig. 49. 



Black and white screen 

 placed over positive and 

 showing only one of the 

 positives. 



^sssmsffissm 



Fig. 50. 



Completed negative 

 of one of the images. 

 Entire surface is now 

 occupied by image which 

 on original only occu- 

 pied one-third. 



the best are those ruled in groups of threes, one line being in a reddish - 

 yellow, one in a yellowish-green, and the other in a blue-violet colour. 

 The screens made by Mr. Brasseur have 531 lines per inch, with no 

 mistakes in any inch of more than one fifty-thousandth of that space. 

 When the negative has been obtained a positive on glass must be made. 

 This positive apparently does not differ from ordinary positives ; but 

 when examined under the Microscope it is found to consist of three 

 interwoven images corresponding with the three sets of lines of the 

 taking screen (fig. 48). Suitable printing plates must now be made 

 from each one of these interwoven images. This is done by placing 

 over the positive a black and white screen ruled in such a way that 

 each black stripe exactly corresponds to two adjacent stripes, and each 



* Annual Report of Smithsonian Institution, 1900, pp. 523-6 (5 figs, and 1 

 coloured plate ; and The World's Work, Dec. 1900. 



April 16th, 1902 B 



