U) ( ON THE EOK^[A'L'lON OF DEFINITE FIOUUES P.V 'I'HE DEPOSITION OF DUST. 
uiu' tonus (tio-. 50). Even small specks ot‘ dust in tins tibroiis form act verv strongly 
ill the same Avay as the ])in or rough edge of a glass in inducing deposits to take 
place. It the plate he charged with negative electricity, then a deposit much finer 
in character is ])roduced (tig. 51). 
It is remarkable that these tigures depositeil by a dust-laden atmosjihere, 
should he so shar[) in outline and definite in form. They originate, no doubt, 
in the currents set up by the warming of the plate, but that these feeble 
currents should so completely and jiersistently ju'event the deposition of dust at 
certain places, and determine its precijhtation at others, was hardly to be anticipated. 
Especially may reference be made to the singular action of the ])iu both near and at 
a distance trom the i)late, and the ajiparently complicated wav in which obstructions 
act in altering the form ot the deposits. The formation of the tigures taking place 
as readily on copjier or other metals, as on glass or ebonite, indicates that the 
|)henomena are not purely electrical. 
It is hoped that by the fore^going records and descriptions of these singular tigures, 
jiliysicists may be enabled to e.vplain their formation. 
I wish to record that this investigation was carried out in the I )avy-Faraday 
Laboratory at the lloyal Institution, also that my best thanks are due to my 
assistant, Mr. Olaf BiiOCK, for the important aid which he has given me. 
