Mineralogy and Geology. 265 
is produced, as in the films formed on metallic plates by Nobili’s pro- 
cess, and by heat, as investigated by the author of this communication : 
or, again, as in mica which has become laminated, &c. But in these 
ases the modus operandi is well understood ;—in the former, from the 
enormously high refractive power, and in the latter from the crystalline 
struc In the case of China ink observed by the author, the ellip- 
ticity appears equally, whether it be in the form of a film or in a solid 
mass—though it is only seen in the purest emia In the numer- 
ower. may s 
theory proposed independently by M. f. Cauchy and by Mr. Tovey be not 
more easily applicable,—since it requires nothing but the very simple 
and admissible hypothesis, that the molecules of ether, for a minute 
depth within the surface, are unsymmetrically distributed. (See the au- 
thor’s treatise on the Undulatory Theory applied to Dispersion, ~ 
In various substances containing but a very small proportion of metal, 
ellipticity has been detected, in addition to those enumerated by the au- 
thor on a former occasion. Among these are Prussian blue, and the 
meteorite from the Cape of Good Hope, described in the Philosophical 
Transactions, 1839 and 1840 »—-which’contains only about 33 per cent. 
of protoxyd of iron, very small portions of oxyds of ee and chrome, 
and a trace of metallic iron, (see Phil. Trans. 1829, i, 8 
Il. MineraLocy anp GEOLOGY. 
1. Analysis of the American Mineral Nemalite ; by Prof. ConNnELL, 
(Proc. Brit. Assoc., from Athen., Sept. 26, No. 987 -)--This~ mineral 
bears a striking resemblance to asbestus, so tha t by the eye it can hardly 
be distinguished from it. It was first chemically examined by Mr. Nuttall, 
who ascertained that it differs entirely in constitution from asbestus, 
and concluded, from his experiments, that it consists essentially of mag- 
hesia and water, with a little oxyd of iron and lime. It was subse- 
ire, ries by Dr, Thomson, according to whom it also contains 
123 per cent. of silica. The constituents found by the latter were— 
fagnchis} ‘ i s 3 . ; §1°721 
Silica, - ‘ ; ; ‘ A . 12-568 
Peroxyd of hat . ; : ‘ : 5874 
Water, ; i : : ; 29-666 
99-829 — 
bi result which I have obtained differs somewhat from both the pre- 
ing. According to each of the previous experimenters the mineral is 
soluble in acids without effervescence. But I have found that even per- 
g 
residue when diadslved: The amount of ee was determined 4 
ascertainin the quantity of water collected by ignition in a tu 
German slane- wink seats and ve at one end fused chlorid of 
Szconp content Vol. HI, No. 8.—March, 34 
