1028 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



and requires but simple manipulation. The length of exposure varies with 

 magnification and the diaphragm ; with SteinheiFs aplanatic of 14 cm. focal 

 distance, with diaphragm 4 for a magnification of 10 times, 6-8 minutes 

 are required. Thin sections require longer than thick or deeply stained 

 specimens. All the necessary details of manipulation are given with each 

 packet of the Eastman's paper, but it may be mentioned that after exposure 

 the paper is moistened with water and the image developed with acetate of 

 potash and sulphate of iron. It is then washed in acidulated water, and 

 having been fixed with hyposulphite of soda, is frequently washed, and the 

 sheet is then dried. The time occupied in taking four slides with twenty-five 

 sections each, magnified 10 times, is from an hour to an hour and a quarter. 



In addition to giving an accurate copy of the sections, the method is most 

 useful for reconstruction of the image, and if before cutting Kastschenko's 

 definition planes * are applied, the fine lines appear on every negative, and 

 this renders the copies still more suitable and convenient for reconstruction 

 purposes. 



Ellis's Focusing Arrangement for Photomicrography. — Mr. John 

 Ellis writes us : — " All the focusing arrangements for photomicrography 

 have appeared so defective to me, that I venture to send a description and 

 drawing of the one I use. The rod running the length of the camera carries 



Fig. 246. 



a loose arm, at the end of which is a roller, covered with indiarubber, which 

 is made to revolve by an endless strap passing round a wheel upon the rod. 

 The roller is kept in contact with the fine-adjustment screw of the Micro^ 

 scope by an indiarubber band attached to the base-board and the arm." 



Nelson's Photomicrographic Focusing-screen. — This (the design of 

 Mr. E. M. Nelson) is made by engraving the English and metrical scales, 

 as well as a crossed diagonal, on the plane-glass plate which is used by 

 nearly all photomicrographers. The engraving, which forms a convenient 

 object to focus on, is a scale for measuring the magnifying power. The 

 English scale is divided into inches, teuths, and half-tenths, and the metrical 

 into cm. and mm. The scales are ruled horizontally, one inch apart, across 

 the plate, one on either side of the cross made by the diagonals. The 

 diagonals are not ruled at the points where they pass through the scales, ia 

 order that they may not interfere with the divisions. 



Denaeyek, a. — Resume de la conference publique sur les precedes de reproduction 

 aux encres grasses des cliclies photomicrographiques et des images d'objets scien- 

 tifiques. Expose d'un precede nouveau de photolithograpMe, avec demonstrations. 



" See this Journal, ante, p, 511. 



