Royal Society. 545 
As these subjects are inferior to few in the interest that attaches to 
them, and would be more generally attended to if the mathematical 
calculation by which the reasoning in most of them is necessarily 
conducted could be simplified, any attempt, like that in the work 
before us, to do this, is deserving of our approbation. 
XCIII. Proceedings of Learned Societies. 
ROYAL SOCIETY. 
1836. PAPER was read, “ On an artificial Substance resem- 
Feb, 25.— bling Shell; by Leonard Horner, Esq., F.R.S. L. 
and Ed.: with an account of the examination of the same; by Sir 
David Brewster, K.H., LL.D., F.R.S., &c.”’ 
The author, having noticed a singular incrustation on both the in- 
ternal and external surfaces of a wooden dash-wheel, used in bleach- 
ing, at the Cotton Factory of Messrs. J. Finlay and Co., at Catrine, 
in Ayrshire, instituted a minute examination of the properties and 
composition of this new substance. He describes it as being compact 
in its texture, of a brown colour, and highly polished surface, with a 
metallic lustre, and presenting in some parts a beautiful iridescent 
appearance: when broken, it exhibits a foliated structure. Its ob- 
vious resemblance, in all these respects, to many kinds of shell, led 
the author to inquire into its intimate mechanical structure, and into 
the circumstances of its formation. He found, by chemical analysis, 
that it was composed of precisely the same ingredients as shell ; 
namely, carbonate of lime and animal matter. The presence of the 
former was easily accounted for ; as the cotton cloths which are placed 
in the compartments of the wheel, in order that they may be tho- 
roughly cleansed by being dashed against its sides, during its rapid 
revolutions, have been previously steeped and boiled in lime water, 
But it was more difficult to ascertain the source of the animal matter; 
this, however, was at length traced to the small portion of glue, which, 
in the factory where the cloth had been manufactured, was employed 
as an ingredient in forming the paste, or dressing, used to smooth 
and stiffen the warp before it is put into the loom. These two ma- 
terials, namely lime and gelatine, being present in the water in a state 
of extreme division, are deposited very slowly by evaporation; and 
thus compose a substance which has a remarkable analogy to shell, 
not only in external appearance, and even pearly lustre, but also in 
its internal foliated structure, and which likewise exhibits the same 
optical properties with respect to double refraction and polarizing 
powers. 
A letter from Sir David Brewster, to whom the author had sub- 
mitted for examination various specimens of this new substance, is 
subjoined ; giving an account of the results of his investigations of 
its mechanical and optical properties. He found that it is composed 
of laminz, which are sometimes separated by vacant spaces, and at 
others, only slightly coherent; though generally adhering to each 
Third Series. Vol, 8. No. 50, Supplement. June 1836, 31 
