664 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
giving both English and Continental standards, and accommodating 
objectives corrected for either length. The spacious stage is made of 
aluminium, which is incorrodible ; the dimensions (3f in. square) are 
commodious even for culture slides or serial sections ; the surface is plane, 
with recessed opening to receive a glass plate, light -modifier, or disc- 
diaphragm, if wanted ; removable 
clips are provided, with springs 
shaped and adjusted to hold a 
slide, and yet allow easy move- 
ment about the field of view. 
The substage has long sliding 
movements in the fixed bar be- 
neath the stage, allowing ample 
room for a condenser or polar- 
izer, and exact adjustments are 
easily and quickly made by aid 
of milled knobs extending on 
each side of the sliding bracket, 
on which the ring of the substage 
is centered and affixed instantly 
by means of a single set-screw 
with capstan head. The mirrors 
are plane and concave, of large 
size, and have complete adjust- 
ments on an extensible bar. The 
diaphragms are cone-shaped, and 
have three different sizes of 
apertures. The Abbe illumi- 
nating apparatus has a condenser 
of 1*20 N.A. and iris diaphragm 
with complete movements. A 
condenser of 1*40 N.A. can be 
substituted, if preferred. A set 
of stops are also furnished for 
dark-ground illumination. 
A modification of the swing- 
ing substage and mirrors has 
been effected, whereby the exten- 
sible mirror-bar slides in another 
bar which swings from a joint on 
the under side of the swinging- 
bar carrying the substage. This construction allows the substage and 
mirrors to swing independently of each other, click-stops indicating when 
either or both bars are in the optic axis of the instrument ; and permits 
the substage to be swung aside entirely and the mirrors alone to be then 
swung into positions for central or oblique illumination, without inter- 
ference from the substage. The mirrors can be likewise swung aside 
completely to permit the use of direct illumination, with or without 
substage apparatus. These movements contribute much to convenient 
and rapid use, as it is unnecessary to remove and afterward return 
the substage, or mirrors, or any other part. In this instance the stage 
is made somewhat narrower to allow the substage to swing clear aside. 
