C74 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
for gaslight, and only admitted of magnifications up to 20 times. The 
present apparatus, in which the electric light is employed, allows of work 
at any magnification, from the lowest to the highest attainable with 
immersion apochromatics. 
The general arrangement of the apparatus is seen in the figure (fig. 74) 
which represents the ground plan of the photographic room. T is the 
work-table, I the lantern with the electric lamp L, B the first illumi- 
nating lens, II the optical bank with slides 1 to 3, K a zinc vessel with 
water supply for cooling the lantern, III the stand in the dark room, 
B the photographic frame. 
Fig. 74. 
The electric lantern consists of a wooden box 95 cm. high, containing 
a Biirgin arc lamp. In the side wall is a window for the observation of 
the arc, and in the front wall fits a metal plate, which is movable trans- 
versely by screws, and carries a wide tube containing the first illumi- 
nating lens. Between lamp and lens is a copper cooling vessel, with glass 
sides, through which a stream of cold water passes. For centering pur- 
poses the lamp can be displaced transversely on a slide by means of 
a winch worked from the outside. Each of the two carbons is provided 
with an independent movement. The most advantageous distance for 
the carbons was found to be 4-8 mm. 
The optical bank, 61 cm. long, is provided with prismatic rails, and 
rests on two iron supports built into the wall of the room. Three slides 
move on it, the first of which carries the illuminating system, the second 
the object-stage, and the third the objective. The illuminating system 
consists of a double lens of 21 cm. focal length. Besides this lens, slide 
1 also carries a red glass plate which can be thrown out to one side, and 
a metal ring for the reception of coloured glass plates. 
Slide 2 supports a brass frame on which the object-stage hangs. 
This stage, which is movable by screws, horizontally and vertically, can 
ba readily put on or off. 
Slide 8 carries a rectangular metal plate in the ring of which 
the objective is screwed. For high magnifications this objective-holder 
can be removed and replaced by a large Zeiss Microscope. In front of 
the objective is a diaphragm which can be thrown out to one side. 
