Mr Douglas Rudge, A dust electrical machine. 249 
A dust electrical machine. By W. A. Doucuas Rupee, M.A., 
St John’s College. 
[Read 19 May 1913.] 
| In the course of some work on atmospheric electricity carried 
on during the past three years, the author has shown that very 
considerable charges of electricity are given to the air during 
the raising of dust-clouds, whether by wind blowing over the 
surface of the earth, or by the motion of motor cars, etc. along 
dusty roads, or in general by raising a dust by any method. The 
kind of electrification varied with the nature of the dust itself, 
and the magnitude of the charge depended to some extent upon 
the fineness of the state of division. During dust-storms, hollow 
insulated vessels arranged to catch the dust may be charged to 
a potential of some thousands of volts. In a systematic study of 
the methods used for raising clouds, and determining the charge 
upon the dust particles and upon the air accompanying them, it 
was noticed that small sparks could occasionally be obtained 
from insulated vessels used to collect the dusts. Some simple 
pieces of apparatus have been constructed, by which it is possible 
to obtain considerable charges of electricity from the raising of 
a dust cloud. As shown in a previous paper* any kind of dust 
can be made to yield charges of electricity, and in the apparatus 
to be described, sand, road dust, flour, sulphur, iron filings, etc. 
may be employed as the working substance of the machine. The 
apparatus may be constructed very simply, but the form shown 
in the figure is the most satisfactory. 
The machine consists of a chamber A in which the dust is 
raised by sending into it a current of air from the bellows. The 
dust is carried into the chamber B. This consists of a brass 
tube about 25 x 5cms. insulated from the rest of the apparatus 
by an ebonite plug #. The dust escapes through 0. In the 
dry African climate, the chamber B can be dispensed with, the 
tube leading from A serving as a collector and sparks will fly from 
it when a rapid current of dust is passing. 
The effects produced by the machine are very remarkable 
with dry dust and a dry atmosphere, as the dryness allows of a 
very fine state of division of the dust. With an apparatus of 
the dimensions shown sparks up to 5 cms. in length have readily 
been obtained, and “brush” discharges will fly from the tube if 
the atmospherical conditions are suitable. The air escaping from 
* Phil. Mag., April, 1913. 
