VI. 0)1 the Fonnation of Definite FiffiD-es by the Dejjositioii of Dust 
By W. J. llussELL, Fh.D., F.li.S. 
Received Jaimary 29,—Read February 19, 1903. 
When trying’ soni6 expcriniBiits which had an object other than that described in the 
following communication, it was noticed that a fine powder when allowed to settle 
on a slightly warmed plate produced figures which were remarkably clear and 
definite. So striking and peculiar were these figures, and so simple were the 
conditions of their formation, that a careful study of them was undertaken. These 
figures are so clear and sharp that it is easy to obtain exact photographic records of 
them, an important point, for, at present, it does not seem possible to offer a simple 
explanation of the complicated relationships which exist between the external 
conditions and the figures formed. Sensitive as these figures are to outside 
influences, the forms they assume are very characteristic of different conditions, are 
perfectly constant, and are easily produced. 
The general method of obtaining these figures is as follows ; The plate on which 
the figure is to be deposited is best supported on three pins about l-g- to 2 inches 
hiuh, and the dust most convenient to use is that made by burning magnesium 
ribbon. It is kindled and allowed to burn in a receiver. A circular glass dish with 
straight sides, about 4 inches high and 9 inches in diameter, is a convenient form 
of vessel to use; and if the vessel be large enough (there should be about 2 inches 
lietween the plate and the inside of the receiver); the shape and the material 
of this dust containing vessel is not of much consequence. After the magnesium has 
burnt out, this receiver is allowed to stand for a minute or so, and it is then placed 
over the plate on its stand and allowed to remain there for six to seven minutes. 
On removing,' it a clear and definite figure will be found to have formed on the plate.^ 
If the plate has been a square one, then a cross consisting of four rays, each starting 
from a corner and meeting, but not necessarily joining, in the centre, is produced. 
If the corners be varnished or covered by a small piece of tinfoil (fig. 1) the cross is 
still formed. 
* A photograph of the figure was obtained by placing the plate on a varnished black backgiound, 
illuminating it by an arc lamp, so that the beam of light fell upon it at an angle of about 30 degrees, and 
the camera was placed directly in front of the plate. Process plates were used, and the exposure was fiom 
two to two and a-half minutes. 
VOL. cci.— A 336. 2 b 
28.5.03 
