ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
531 
may be desired. It is made of thin metal, and may bo quickly attached 
to the bottom of the indicator-dropper and quickly placed in any position 
where desired. 
Other accessories made by additions to the focus-indicator will be 
described later. 
Fig. Go. 
Filar Micrometers.* — Prof. W. A. Rogers considers that there are 
two requirements in the construction of a good filar micrometer to which 
manufacturers have given too little attention, viz. equality in the 
diameters of the fixed and movable threads, and ease and uniformity in 
the movement of the measuring screw. 
The author considers that as regards uniformity in diameter, quartz 
fibres are far superior to spider lines. They appear to be truly circular 
and any required diameter can be easily obtained. 
The second difficulty may be met by the use of a long spring instead 
of the usual short stiff one for keeping the slide in contact with the end 
of the screw. For this purpose nearly the whole length of the frame 
can be utilized by the use of guide-pulley? at one end. thus allowing the 
spring to lie parallel with the sliding plate. 
Micrometers made for the author on this plan by Bausch and Lomb 
have given very satisfactory results. 
Reichert’s New Heating Apparatus. | —This apparatus, fig. 69, is 
used for the stage described on p. 383. It was designed by Dr. 
Spietschka in order to obtain a uniform heating of the hot stage during 
the course of prolonged investigations. A is a large vessel containing 
15 Proc. Amer. Soc. Micr., xiv. (1893) p. 132. 
f Reichert’s Catalogue No. 18 (1892). 
