864 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Near the bend at b the tube is cut through ; and in the circular 
apertures fit glass plates which give passage to the light, and serve to 
protect the objective and condenser. Between these plates in the middle 
of the box is the crystal holder which consists of a small strip of glass 
resting on two supports. The whole box is coated with asbestos in order 
Fig. 95. 
to reduce the radiation, as well as to protect the hands of the observer 
from contact with the hot metal. For the further protection of the 
Microscope, the plate P, which rests upon the stage, is coated with 
asbestos on its under side, and is connected with the heating apparatus 
by four glass feet. In the case of large instruments with movable 
stages, the apparatus is fastened to the stage by the binding screw S. 
The heating of the crystal is effected by a Bunsen burner g g\ 
the tube of which cuts through the inclined arm of the box, and lies 
with the greater portion of its length in the horizontal part. At g’ 
it is bent at a right angle, and the part opposite the opening of the 
box is slit for the exit of the gas, which burns with a broad blue 
flame. 
The position of the burner can be adjusted so that the flame 
approaches or separates from the object. By this means a very pre- 
cise regulation of the temperature can be effected. 
At the bend of the burner a tube r can be inserted which serves 
for the introduction into the box of water vapour or cold air. For 
this purpose the two branches of the tube can be connected respec- 
tively with a flask of boiling water and with a bellows. By the 
latter a rapid cooling can be effected, or a blowpipe flame produced when 
a tube with circular opening is fitted over the ordinary slit of the 
burner. 
The reservoir of the thermometer is in the shape of a liorse-shoe, the 
two arms of which rest on the object-holder, and enclose a space of about 
7 mm. square which is occupied by the crystal, so that a uniform heating 
of thermometer and crystal is assured. 
The second apparatus, represented in fig. 96, is for temperatures up to 
a red-glow. The source of heat is an electric current passing through 
two pieces of platinum foil. On a rectangular stage of slate, with wide 
