Proceedings. 5 



The following note " On Dust Figures " was also read 

 by Professor ARTHUR SCHUSTER, F.R.S., the author : — 



"In the house which I occupy at present there are two 

 sitting rooms, separated by a wide opening, with a slightly 

 curved top. The opening is closed by a curtain hanging 

 down from a pole about four inches above its highest point. 

 The former tenant used a wooden pole on one side of the 

 opening. That pole was removed, and I substituted a brass 

 pole on the other side of the wall, so that the wall above 

 the opening, where the previous pole was, is now perfectly 

 clear on that side on which the previous pole had been 

 placed. I took possession of the house two years ago. The 

 wall paper in both rooms was carefully removed, the walls 

 cleaned, and a white paper put up, which was subsequently 

 distempered with a uniform tint. About a year ago I 

 noticed, what seems to me to be a very remarkable fact. 

 A black band was seen stretching across the wall above the 

 opening, exactly at the place from which the pole had been 

 removed. This black band, it was ascertained, is due to 

 dust having deposited in greater quantity where the pole 

 had previously been than in other places. Leaving out of 

 account any possible effect of the brass pole on the other 

 side of the wall, we are driven to the conclusion : that a 

 wall which has been stripped of its paper, been washed and 

 then been repapered, shows, by the way the dust deposits 

 on it, the place where, two years ago, a wooden pole had 

 been placed, while the old paper was still on the wall." 



(Added, October 2j.) — "Since writing the above, and 

 partly in consequence of the remarks made by some of the 

 speakers at the meeting, I have made further inquiries, and 

 heard from the former tenant that he believes an iron beam 

 is imbedded in the brick wall at the place where the dust 

 line shews. This beam was not visible when the paper was 

 removed, and is therefore completely covered with plaster. 

 Nevertheless it may account for the dust mark by causing 



