32 
Ordinary Meeting November 29th, 1881. 
E. Angus Smith, Ph.D., F.E.S., &c., in the Chair. 
The following letter from Mr. Joseph Sidebotham, 
F.E.A.S., was read: 
“ Some few years ago when I was at Mentone, I wrote to 
yon concerning the aniline colours, so much used on the 
Continent in water colour drawings. Since that time 
Holman Hunt and others have called attention to the fading 
of these and some other colours prepared for artists, and I 
hoped the practice of making and using these colours had 
ceased ; however, I find this is not the case. A friend of mine 
was on his way to the South of France, and I asked him to see 
if these colours were still sold and used, and he tells me they 
are extensively, and sent me cakes of them ; he also sent 
the enclosed sheet of the colours on drawing paper, half of 
it having been exposed to the light, a fortnight, the other 
half covered up. He thought that by putting gum over the 
colours they might be made more permanent, and you will 
see he has put a band of gum across them; the colours ex- 
posed have faded in a great degree, some of them almost 
disappearing. The band of gum has retarded the fading, but 
the colours are even there much lighter and all the bright- 
ness gone. It is most desirable that artists should entirely 
give up the use of all these colours, and then the makers 
would cease to supply them. When we see the sad effects 
of a fortnight’s light upon them, what can we expect to see 
in drawings hung on the walls of a room for a few years ? ” 
“ On Cyclic Motions in a Fluid, and the Motion of a Vortex 
Eing of varying Curvature,” by E. F. Gwyther, M.A. 
The possible kinds of fluid motion are divided into irro» 
tational, which is either cyclic or acylic, and rotational or 
