1888 - 89 .] Mr John Aitken on Dust Particles. 
145 
cm. If this be so, then the holes P . . . P are drilled at 1 
cm. intervals, the first being at 1 cm. from lowest position of 
the piston. In the instrument I have constructed the cylinder 
has an area slightly less than 1 square cm. In graduating it, 
the length of cylinder required to hold 10 c.c. of water was care- 
fully ascertained. This length was then marked on L, and divided 
into 10, and the holes bored. By this arrangement, when the collar 
is moved up one hole, 1 c.c. of air is taken into the cylinder ; if 
moved up two holes, 2 c.c. are taken in, and so on. To enable a 
number of tests to be made quickly with exactly the same quan- 
tity of dusty air, a pin, Q, is put into one of the holes, P, at the 
desired capacity. This pin stops the outward movement of the 
collar at the correct position, and enables the successive measure- 
ments to be made accurately as well as quickly. 
The whole measuring apparatus is supported by the wooden stand 
Y, to which it is fixed by screws through the flange X ; and Y is 
securely clamped to the table under the test-receiver. 
In working with this apparatus, one or two trials are first made 
to find out the amount of dusty air that will be most suitable for 
testing. Suppose we find 1 c.c. gives too few drops and 5 c.c. gives 
too many, we may select to work with, say, 2 c.c. The pin Q is 
accordingly put into the second hole, and testing begun. The handle 
of the stopcock F is put up against the stop H x ; the piston is then 
drawn out till stopped by the pin Q at 2 c.c. ; the stopcock turned 
till it is stopped by H 2 , the piston pushed down, and the 2 c.c. of 
air sent into C. From this it will be seen that very little time is 
required to measure the air ; practically only the time required to 
pull out and push back the piston, and for each succeeding test, of 
which perhaps ten may be made to get a good average, exactly the 
same amount of air is measured and sent into D. After the air is 
in D it loses but little of its dust, as it has not time to fall down 
through the long vertical column of dustless air underneath it before 
it is carried into the receiver. 
By working in the manner above described, we can by means of 
the cylinder and piston measure accurately any quantity of air from 
10 c.c. down to 1 c.c., and even to J c.c., if a hole is drilled in the 
right place. But if we wish to measure smaller quantities, then 
we must use the part of the apparatus shown at B, which is 
vol. xvi. 7/5/89 K 
