232 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
MICROSCOPY. 
a. Instruments, Accessories, &c.* 
(i) Stands. 
Microscopes and their most important Accessories for Crystallo- 
graphic and Petrographical Investigations.-)- — Herr C. Leiss gives a 
full descriptive account of the various Microscopes and accessories for 
crystallographic and petrographical purposes which have been supplied 
by the firm of Fuess, of Berlin. 
Among the instruments which have not already been described and 
figured in this Journal are the following : — 
Small model (IV. and V.), shown in fig. 27. The stand is of the 
tripod form. The rack-and-pinion adjustment is sufficiently delicate 
for the use of fairly high objectives, such as Nos. 7 and 9. At the lower 
end of the body-tubes are the screws c for centering the objective. The 
latter is not screwed on, but is held by a spring clamp h in a short conical 
adapter. Immediately above the clamp h at K is a slit for the reception 
of the Biot-Klein quartz-plate, gypsum, and mica plates, &c. In the 
lower part of the body-tube is the opening for the analysing prism N 
of the Glan-Thomson construction, which gives the greatest field of 
view. Another slit at B serves to receive the Bertrand lens. The 
draw-tube R is provided with a projecting ring, which carries the index 
for the divided circle of the auxiliary analyser A used for stauroscopic 
measurements, &c. The ocular lens of the Huyghens eye-piece is held 
in a movable socket, so that each observer can adjust on the cross-wires. 
For the observation of axial images, in connection with the Bertrand 
lens a Ramsden eye-piece is provided which is furnished with a glass 
micrometer. 
The rotating stage is divided in degrees, and carries a vernier reading 
to 5 minutes. On its upper surface are two rectangular divisions. 
Under the stage, attached to the stand is the socket H, which is 
adjustable by rack and pinion, and carries the polarising nicol. Above 
the polariser is screwed a condensing lens. For the interchange of 
parallel and convergent light there is a special arrangement for the 
rapid insertion and removal of the hemispherical lens for convergent 
light. In the hollow space between the base-plate of the stage and its 
upper plate is a small plate, from which projects an arm terminating in 
a ring which holds the hemispherical lens. When the polariser with 
its weak condensing lens is raised, it catches up the hemispherical lens 
and raises it with it up to the plane of the object-stage. When the 
polariser is lowered, the hemispherical lens follows its movement until it 
reaches the ring of the movable arm, when it can be moved aside out of 
the axis of the Microscope. 
The larger models (I.-III.) have been described in this Journal, 
1886, p. 843 ; 1891, p. 393 ; and 1892, p. 665. 
Improvements which have been recently introduced are an arrange- 
ment for rotating the inner nicol, and the insertion of an iris-diaphragm 
* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) Illu- 
minating and other Apparatus; (4) Photomicrography; (5) Microscopical Optics 
and Manipulation ; (6) Miscellaneous. 
t Zeitschr. f. Ang^wandte Mikroskopie, i. (1895) pp. 97-109, 129-38, 193-206. 
