40 
The way he found answered best in mounting these lovely 
little plants is, after he had washed and prepared them 
in the cell, to put them with a little 'plain water, 
place a glass cover over them, carefully avoiding the 
enclosure of any air bubbles, and having taken up any 
moisture about the edge of the cell with blotting paper, to 
seal them up with gold size. In some cases the colour goes, 
but in others the bright green colour is retained for many 
years. 
In conclusion, he said there was a want among investi- 
gators in this branch of microscopic work of a uniform scale 
to which to make their drawings. Each man has his own 
scale, and this makes the comparing of drawings, very much 
more difficult than if a uniform scale, say 400 diameters were 
adopted, by means of which one man might at once and 
without the slightest difficulty compare his drawings with 
those of other fellow- workers. 
PHYSICAL AND MATHEMATICAL SECTION. 
November 8th, 1881. 
Joseph Baxendell, F.RA.S., President of the Section, in 
the Chair. 
“ Note on a Passage of Pollux relating to the formation 
of Purple Dye,” by James Bottomley, D.Sc., F.C.S. 
At a meeting of the Society on November 18th, 1879, I 
gave a short passage from Musgrave containing a quotation 
from Pollux. From this passage it was inferred that the 
