119 
The quantity of soluble silica is not more than might be 
expected in any specimen of lime and cannot be attributed to 
the action of the sand on the lime. The quantity of BC? is 
equivalent to 49:9 of CaO, and the remainder of the lime ap- 
peared to be partly in the form of sulphate, and probably partly 
in the form of CaCO*, CaH?O?, since treatment of the mortar 
with water failed to extract any appreciable quantity of hydrate. 
The water is more than would be combined in the sulphates, so 
that perhaps a small quantity of the CaCO* was in the hydrated 
form, such as is precipitated spontaneously from a solution of - 
CaH’O? in syrup. 
November 9, 1868. 
The PRESIDENT (PROFESSOR SELWYN, D.D.) in the Chair. 
The following new Fellows were elected : 
H. JAcKSoN, M.A., Trinity. 
T. Dats, M.A., Trinity. 
G. H. Darwin, B.A, Trinity. 
In noticing the presents, the President called attention to a 
beautiful engraving of the nebula in the sword-handle of Orion, 
presented to the Society by Lord Rosse. 
The Astronomer Royal made some remarks on the en- 
graving, calling attention to the fact that it was the first in 
which dark stood for dark sky and light for the brighter parts. 
Communications to the Society: 
: if 
(1) On the factorial resolution of x" ~2cosna+—. 
z 
By the AstrRonoMER Rovyat. 
This was a proof of the well-known resolution by the use 
of ordinary algebra, without the aid of imaginary quantities, 
against the use of which as a mode of education the author 
of the paper spoke strongly. 
