140 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



which is 6 in. square, is made of the best thin white glass in the 

 .same manner as Mr. Hardy's "flat bottle," 



In using the Microscope, the mirror and carrier are unscrewed 

 and placed on the opposite side of the tank from the Microscope, the 

 light being reflected in a line with the body-tube. The objective was 

 also screwed in the substage by an adapter and focused by the 

 substage pinion. 



Bostwick's Absorption Cell.*— Mr. A. E. Bostwick has devised a 

 cell for obtaining the absorption spectra of liquids which have but 

 little selective absorption, and which would therefore have to be used 

 ordinarily in large quantities. 



The cell is a rectangular box, 6 in. by 3 in. by 3 in. The bottom 

 and the two ends are of wood, covered with shellac, and the two sides 

 of looking-glass, cemented to the wood, so that the box is water-tight. 

 The reflecting surface of the glass is turned inward, and at each of 

 two diagonally opposite corners the amalgam is scraped away so as to 

 make a vertical slit about 2 mm. in width. One of these is placed 

 close to the spectroscope slit, and through the other a parallel beam 

 of light is admitted. It is evident that the box may be so placed that 

 the beam will be internally reflected in it a number of times, depending 

 upon the angle between the two, and will finally pass through the 

 second slit into the spectroscope. The length of its path through the 

 cell may therefore be varied indefinitely by turning the latter, and is 

 limited only by the decrease in intensity caused by general absorption 

 — not only in the liquid, but also at each reflection. With mirrors 

 of polished metal the result might be even better, since the absorption 

 in the glass would be eliminated. In this case, however, the number 

 of liquids which could be used in the cell would be somewhat 

 limited. 



Verick's, Benecke's, and Moitessier's Photo - micrograpMc 

 Cameras. — The first of these cameras by MM. Verick (fig. 28) allows 



Fig. 28. 



of four negatives being taken successively. It consists of a tube 

 fitting over the body-tube after the eye-piece is removed, carrying a 

 box C, with a central opening B, closed by a movable shutter A. 



* Amer. Journ. Sci., xxx. (1885) p. 452. 



