ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
367 
relief two brass segments ( a ' V c', fig. 61 ; V c’ } fig. 63) opposite eacli 
other across the diameter K L (figs. 61 and 62). On the glass slide and 
circular collar rests the movable cover-glass, which is of the same thick- 
ness as the segments a' b' c' (figs. 61 and 63). In order that it may come 
in contact with the lower glass slide it is cut by two segments correspond- 
ing to the two which are on the circular collar. By this means the cover- 
glass can receive no movement of rotation. For convenience of removal 
it is cut across the top in the direction x y (figs. 61 and 65), normal to 
that of the segments. 
The ring of compression (fig. 64)" is a ring of brass, of diameter 
a little less than that of the ring fixed to the base-plate. It is provided 
with a screw which engages in the screw-thread on the ring fixed to the 
base-plate. It has a diameter of 44 mm. and is provided at the top 
with a circular milled head (fig. 64, T U, T' U'), and below with a 
circular rim of 6 mm. (fig. 64, R S, R' S') which serves to augment 
the surface of compression on the cover-glass 0 (fig. 61). 
The advantages claimed for the apparatus are the large field of view 
for microscopic observation, the condition of immobility of the cover- 
glass, and the possibility, by means of the screw, of insensibly increasing 
or diminishing the pressure. 
Compressorium.* — Prof. H. E. Ziegler has made an improvement in 
the compressorium recently devised by him.j* In the original apparatus 
only a small portion of the water passes beneath the cover-glass, for 
most of it flows between the caoutchouc ring and the lower glass plate. 
This is of little consequence when the stream of water is sufficiently 
strong, and the object is not too small ; but if the object is so small that 
by the compression the space between the cover-glass and the lower 
glass plate is very narrow, the water beneath the cover-glass is almost 
completely at rest, and nearly all the water which flows through the 
apparatus takes its course between the caoutchouc ring and the lower 
glass plate. 
The author has therefore added to the apparatus an arrangement by 
which all the water flowing through the apparatus must take its course 
beneath the cover-glass. For this purpose the caoutchouc ring at two 
opposite points is pressed in upon the lower glass plate by means of two 
pins, so that by the compression at these points there is no interval 
left between the ring and the plate. The space between the lower glass 
plate and the ring is thus divided into two parts ; and the upper plate is 
so adjusted that the openings of the tubes conveying the water are 
brought over these parts. 
C5} [Microscopical Optics and Manipulation. 
Improved Method for the Microscopic Investigation of Crystals.* 
Mr. A. E. Tutton calls attention to an important memoir on the micro- 
scopic determination of crystals, contributed by Prof. Klein to the c Sitz- 
ungsberichte ’ of the Berlin Akademie der Wissenschaften for January 
31, 1895. In this communication a description is given of a new stage 
goniometer, which allows of the examination of many of the principal 
zones of a crystal with one and the same setting of the crystal on its 
* Zool. Anzeig., xvii. (1891) pp. 471-2..; [f See this Journal, 1894, p. 759. 
X Nature, li. (1895) PP- 608-11. |j 
