560 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
MICROSCOPY. 
a. Instruments, Accessories, &c.* 
(1) Stands. 
New Mieroscope.j — The firm of Richards & Co. offer for sale a new 
Microscope, the stand of which is made entirely of brass. The stage is 
extra large, 9‘5 by 8*5 cm., and consists of vulcanised rubber bolted to 
heavy brass stage-bed 5 mm. thick. The condenser is of the double- 
lens system, and is fitted with an iris-diaphragm, beneath which is a 
ring for the reception of blue or ground glass, &c. The eye-pieces and 
objectives furnished with this stand are Reichert’s standard quality. 
(2) Eye-pieces and Objectives. 
Eye-Piece with Graduated Iris-Diaphragm. — Dr. W. Cowl de- 
scribes and explains the advantages of an eye-piece provided with an 
seen in the figure, the iris-diaphragm takes the 
place in the Huyghens’ eye-piece of the usual 
fixed diaphragm. It is provided on its edge with 
a scale, each division of which corresponds to a 
doubling of the diameter of the aperture, begin- 
ning with 1 mm. The numbers on the scale cor- 
respond to the area of the field of view. 
Amongst the advantages of the apparatus are 
— a more acute perception of details in the field 
of view, owing to the exclusion of neighbouring 
parts of the preparation ; the exclusion of un- 
necessary light ; the possibility of varying the 
magnification by changing the eye-piece without 
the necessity of adjusting the Microscope anew, 
since the iris-diaphragm only slides in the body- 
tube up to the diaphragm, i.e. up to the plane of 
the image formed by the objective. 
Goerz’s New Double Objective. § — The re- 
moval of the error of astigmatism in a photo- 
graphic objective requires a crown-glass of higher 
refractive power than that of the flint-glass con- 
nected with it, whereas the condition for the compensation of the spheri- 
cal aberration is that the refractive power of the crown-glass must be 
less than that of the flint-glass. The Goerz double objective is the 
result of a successful attempt to meet these seemingly incompatible 
conditions. 
Each of the two halves of this double objective consists of three 
lenses. Theoretically, these could be either a negative flint-glass b 
enclosed between two positive crown-glasses a and a' (fig. 85), of which 
a has a higher, and a' a lower refractive index than b; or a crown-glass a 
* 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 Amer. Mon. Micr. Journ., xvii. (1896) pp. 217-S. 
% Anat. Anzeig , xii. (1896) pp. 178-80. 
§ Oentral-Ztg. f. Optik u. Mech., xvii. (1896) pp. 131-2. 
iris-diaphragm. As 
Fig. 84. 
