646 
PROFESSORS A. W. REINOLD AND A. W. RUCKER 
Description of the Apparatus. 
The film box was rectangular in shape, 20 cm. long, 10 cm. broad, and 17 cm. high. 
It was made entirely of thick plate glass, with the exception of the cover, which 
was of ebonite and about half an inch thick. The cover fitted accurately into its 
place, and to it were attached the thermometers, hygrometer, supports for the film, &c., 
so that all the apparatus connected with the films could be removed from the box by 
lifting the cover. 
The supports for the films are shown at A, B, A', B' (Plate 33, fig. 2). A and A' are 
cylindrical platinum cups, 20‘8 mm. in diameter, with carefully turned edges. They 
are screwed to brass tubes C and C', the upper portions of which carry rackwork and 
are moved up and down the larger tubes D, D', by the pinions seen at E, E'. The 
supports for the pinions, as well as the tubes in which the racks slide, are attached to 
brass discs F, F' (figs. 1 and 2), the lower faces of which are ground plane, and rest, 
when they are in their places, in good contact with the top of the ebonite cover. The 
holes in the cover, closed by these discs, are large enough to allow the upper cups to 
pass freely through, so that the latter may be introduced and adjusted to their proper 
positions after the cover has been put in its place. 
The cylindrical rings B, B', are the lower supports of the films. They are about 
5 mm. deep, of the same diameter as the upper cups, and are screwed to platinum 
wires bent at right angles and soldered to brass rods FT, H'. 
These rods pass through tubes K, K', fixed to the ebonite cover. By the ebonite 
buttons a ., a, the platinum rings can be turned on one side in such a way as to allow 
the upper cups to be brought into contact with the soap solution, with which the floor 
of the box is covered to a depth of 2\5 mm. 
Both the upper and lower supports for the films can be unscrewed, and others of 
different size or material substituted for them. We have used (as already stated) 
platinum rings of 20• 8 mm. and 32‘5 mm. in diameter respectively, and occasionally 
glass rings 32'5 mm. in diameter. 
In order to maintain one or other of the two films thick, or to thicken them after 
they had become thin, two different methods were adopted. For carrying out the first 
method, strips of linen were cut about 16 mm. broad, and long enough to pass one and 
a half times round one of the upper cups. Each strip was folded so as to have hall 
its original width, and was wrapped round the cup in such a way that its edge pro¬ 
jected above it, and formed a cavity into which liquid could be poured. It was secured 
in its place by cotton thread. Liquid was supplied to the cavity formed in this way 
by the bent glass tubes L, L', which were open at the top, and were drawn out to 
conical terminations below. They were supported by corks placed in holes cut in the 
cover, and could be turned round or moved up and down, so as to bring their points 
just over the cavity formed by the linen wrappers. By pouring a little of the soap 
solution down the tube, the linen could be made to supply liquid at a greater or less 
