ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
109 
flame chamber ; at the back another short tube B slides easily, one end 
of this inner tube carries the equiconvex lens mirror, while the other is 
closed and made dead black. 
When parallel rays are wanted the mirror is inserted, and the tube 
pushed home, as in fig. 6, as far as it will go, it will then be found to 
be centered and focused to the flame. This plan saves all trouble of 
adjustment. 
The front C is a circular piece of plane glass, fitted to a small piece 
of tube, which slides into A. Fastened to each side of the lamp are 
two aluminium arms D, which carry at their extremities a plane mirror E„ 
This will be found convenient, not only for the illumination of small 
Microscopes when used in an inclined position, because the light can 
be reflected downwards on to the 
mirror of the Microscope, but also for 
dissection, opaque illumination, &c. 
When divergent rays from the 
edge of the flame are required for 
direct illumination in the ordinary 
manner, the arms D with the attached 
mirror E are turned upwards, the 
tube B is withdrawn, and replaced 
with the dead black surface inwards, 
the mirror being then outside. The 
sliding- tube C with the plane glass 
can be withdrawn, and a plate having 
the usual ljby 3/4 rectangular open- 
ing, closed by a 3 by 1 slip, inserted 
in its place ; some observers prefer- 
ring all extraneous light cut out.” 
Leitz’s Micrometer Screw Ad- 
justment.* — This micrometer screw, 
which is shown in section in fig. 7, 
is constructed with particular atten- 
tion to the elimination of all lateral 
motion. The spindle is hollow and 
contains a freely movable steel cylin- 
der, the point of which transmits 
the pressure to the spring. The 
micrometer thread is carefully cut so that the screw works freely in 
either direction, and stops in any position without slipping. 
(4) Photomicrography. 
Leitz’s Photomicrographic Apparatus-t— In this instrument, repre- 
sented in fig. 8, the camera is supported by a metal column which 
rises from a broad iron base on which the Microscope stands. This 
column is adjustable in height and can be fixed in any position by 
thumb- screws, so that the apparatus can be used with Microscopes of 
various sizes. The neck of the camera admits diaphragms of various 
* Catalogue No. 34 of Microscopes and Accessory Apparatus. Ernst Leitz, 
Wetzlar, 1892, p. 12. -j- Op. cit., p. 44, 
Fig. 7. 
