1888-89.] Mr John Aitken on Bust Particles. 
139 
length of tube fixed to an opening in the centre of I. This tube is 
of such a size that the tube D slides easily inside it, and its lower 
end is slightly widened, as shown. The disc I is attached to a wire 
L, which passes through the bottom of the receiver, and is used for 
moving the diaphragm I up and down. In order to avoid the use 
of a stuffing box, with its inconvenient tightness, the wire L projects 
to some distance outside the bottom of the receiver, and is there 
surrounded by an indiaruhher tube M, slightly larger in internal 
diameter than the wire. The tube M is closed at the bottom, and 
firmly attached to the receiver by the pipe 1ST. O is the pipe by 
which the air enters the receiver. It is provided at the lower end 
with a stopcock, while the top is closed, and two side openings close 
to the top are provided for the escape of the air. Over the top of 
this pipe is fixed the deflector P. The pipe O should he small, 
say 2 mm., or the expansion of the air in it will give rise to a 
slight disturbance of the air in the receiver when condensation is 
taking place. Q is the outlet pipe, and its lower end is connected 
by means of an indiaruhher tube with the air-pump. At the upper 
end of Q is a cap K screwed into the end of the pipe. This cap has 
a large cover, which prevents the disc I from rising above its 
proper position. At the lower end of Q is a tuft of closely-packed 
cotton wool, kept in its place by means of a ring. The air enters Q 
through a small hole near the top of the tube; just under the screw 
of the cap S is a magnifying glass for viewing the stage. To 
the under side of its ring is attached a piece of indiaruhher cord, 
which prevents the glass getting scratched and the lens from 
slipping. T is a pipe provided with a stopcock for supplying 
the receiver with water. It is connected by means of an india- 
rubber tube with a vessel of water. U is a bent tube, one leg of 
which passes up the tube D, and terminates just under the closed 
end of D. Both ends of tube U are open. It is soldered to the 
short tube Y, which fits tightly inside D ; it is thus kept firmly in 
its position, hut can he removed when required. 
The two sides of the diaphragm I are covered with blotting-paper 
fastened on with indiaruhher solution. The under side of the top 
plate B is also covered in the same way, hut an opening is cut in 
this piece for viewing the counting stage and for admitting light 
{see XX. fig. 4). 
