ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



437 



little play, is able to follow the inequalities of the coarser parts of the 

 apparatus (e. g. the guides S). Backlash is prevented by a spiral spring 

 which is partly inclosed in the box t ; this spring is made of greater 

 length than usual, so that within the limits of its action there shall be 

 no appreciable variation in the resistance ; the author considers that the 

 large resistance exerted at the beginning of its action by the spring as 

 usually made causes great wear and tear of the micrometer-screw and its 

 bearings, while at the end the resistance is so weak that the drum tends 

 to leave its abutment. In this instrument the drum is a fixture upon 

 the frame S. The drum is divided into 100 parts ; the divisions are 

 read by the lens I', and whole turns are registered upon a millimeter 

 scale, which is read by the lens L 



The stage T carries a frame which is moved between swallow-tail 

 guides by a fourfold screw of steep pitch (not shown in the figure) in a 

 direction perpendicular to that of the slide C Upon this frame the 

 negative is placed, and is held by two clips, p is a special stage de- 

 signed to carry the smaller sized negatives of siderospectrographs. By 

 means of the sliding stage different spectra, which have been photo- 

 graphed upon the same plate, can be brought under the Microscope in 

 succession ; the negatives are illuminated from below by an adjustable 

 mirror. 



Konkoly's Microscope for Reading the Knorre-Fuess Declino- 

 graph.* — Dr. N. v. Konkoly describes this as follows : — Screwed to a 



mahogany base A is a massive brass disc D, on which is the column B ; 

 the latter consists of a tube 3 mm. in thickness, in which a rod is free to 



1889. 



Central-Ztg. f. Opt. u. Mccli., viii. (1887) pp. 217-8 (1 fig.). 



2 H 



