XIV. On the formation of definite figures by the deposition of dust

Abstract

Owing to the kindness of Dr. W. J. Russell, F. R. S., I received in June an advance copy of his paper on the above subject. After reading this paper it appeared to me that all the figures illustrated in it could be explained on well-known principles. I shall therefore do what I can to fulfil the hope expressed by Dr. Russell at the end of his paper that physicists from his descriptions may be enabled to explain their formation. The formation of these dust figures appears to be due principally to three causes : (l) the convection currents set up by the hot plate ; (2) to gravitation ; and (3) to the repelling action of the hot surface. It seems trivial to remind the reader that gravitation plays a part in the formation of these figures, but it is to be feared that it is from not keeping the effects of gravitation fully in view that difficulty has been experienced in explaining them. It is principally owing to gravitation, or rather to an after-effect of gravitation, that no dust is deposited on certain parts of the plate. Gravitation acts on the dust under the plate as well as on the dust over it, thus causing the film of air flowing along the under surface of the plate to be dustfree, all the dust having fallen out of it.