684 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Ftb. 81. 
whole thing becomes simple enough. As the Microscope has to he 
turned into a wide-angled polarizing telescope, all that is necessary 
is to screw a low power on the end of the draw-tube. As the 
light requires to be pnssed through the crystal at a considerable angle 
a wide-angled condenser should be employed, but it need not be achro- 
matic. The objective I found most suitable was a 4/10 of *64 N.A. ; 
but a 1/4 of -71 N.A., or a 1/3 of *65 N.A. will 
do equally well. As the whole of the back lens of 
the objective should be visible through the ana- 
lysing “ Nicol ” the back lens of the objective must 
not be too large, thus a 1/2 in. of *65 N.A. would 
not do so well. The analysing prism may be 
placed either where it is in the drawing or above 
the eye-piece. Practically it works very well above 
the objective, which is the position it occupies in 
“ ordinary microscopical outfits.” 
For the draw-tube a 2 in. objective and a B or 
C eye-piece will be found to answer admirably. 
To set up. — Before screwing the objective in the 
end of the draw-tube, centre the light in the usual 
manner, the “ Nicols ” being turned so as to give a 
light field. Next fix the objective in the end of the 
draw-tube, open the substage condenser to full 
aperture, and put the mineral on the stage. Rack 
down the body so that the objective on the nose- 
piece nearly touches the crystal, then focus with 
the draw-tube exclusively. The substage condenser 
should be racked up close to the under side of the 
crystal. 
(6) Miscellaneous. 
Microscopes and Accessories at the Antwerp 
Microscopical Exhibition.* — Dr. R. H. Ward, in 
his Presidential Address to the Microscopical Sec- 
tion of the Troy Scientific Association, said : — 
“ In this department the chief exhibitors w'ere, 
naturally, the manufacturers, and with only two 
notable exceptions they were of the c Continental ’ 
gr.,up. 
In substage : P, pola- Among the whole it was evident that one, the 
rizing prism; C, sub- Carl Zeiss establishment at Jena, was easily pre- 
stag e condenser. On em inent, on account of the magnitude and variety 
°, f its exhibit - the Wgl> quality of its work, and 
tive 4/10 -64 N.A. ; the extent and importance of its contributions to 
A, analysing prism, recent development of the Microscope, especially 
In draw-tube : O 2 , ob- j n inventing and introducing new optical glasses of 
jective, 2- or 3-im ; refractive indices and in the creation of the 
apochromatic objective. The exhibit included a 
large variety of the well-known Zeiss stands, with 
their different classes and powers of oculars and objectives, and their 
outfit of numerous and ingenious accessories ; also a special stand for 
* Amer. Mon. Micr. Journ., xiii. (1802) pp. 136-40. 
H, Huyghenian eye 
piece. 
