144 Geographical Collections. 
_ Extract of a Letter written on board the Indemnity, arrived in the Downs 
from Demerara.—‘‘ Ship Indemnity at sea, at 3 Pp. M. discovered a rock on the 
starboard beam, distant about three ships’ lengths ; we were then going at the | 
rate of about two and a half miles per hour, with a heavy swell from the N. W. 
With each succeeding swell it was entirely covered, but at intervals it showed 
several feet above water, and perfectly perpendicular. From the mast-head it was 
seen to a great depth below the water, and appeared to be in the shape of a cone. 
At the preceding noon our latitude by observation was 43° 20’ N. and longitude 
by chronometer 25° 10’ W. 

NATURAL-HISTORICAL COLLECTIONS. 
Extract from the Analysis of the Labours of the Academy of Sciences during 
the year 1828. By Baron CUVIER. 
Mineralogy.—Since chemistry, by means of definite proportions, has deter- 
mined the number and relative weight of atoms of different kinds of which 
every chemical body is composed ; since the earths, which were supposed to be 
simple, have been found to be metallic oxides, and silica has to perform in those 
stones where it prevails, the part of a true acid; in fine, since it has been found 
possible to distribute all bodies according to the manner in which they are affected 
by the galvanic pile, the chemical analysis of minerals has received a new direc- 
tion, and an exactness which chemists thirty years ago would scarcely have dared 
to expect; and yet there still remain minerals, and especially silicious stones, 
which, to the present time, we could scarcely believe it were possible to submit 
to the laws, except by supposing that certain of their parts, particularly the silex, 
exist in superabundant quantity over the proportion according to these laws, and 
rather as an accidental mixture than a true combination; and the opponents of 
the theory of definite proportions, not thinking themselves obliged to admit such 
a supposition, draw from these facts very weighty objections against this theory. 
_M. Beudant has devoted himself to extended researches, for the purpose of un- 
folding this kind of phenomena ; and, with this view, he at first applied himseif 
to the study of the salts properly so called, which it was more easy to compose and 
decompose in his experiments. He constantly observed in whatever proportion 
he approximated the elements to each other, that the acid or the base was in su- 
perabundance ; but when once crystallized, the proportions of acid and base were 
the same, provided that the precaution was taken to deprive them as much as ° 
possible of the liquid particles, which are often found lodged between the lamine 
of crystals. In operating upon salts, whose acids themselves are crystallizable, 
the excess of acid crystallizes separately from the neutral salt, and it is more easy 
to mix two different acids in the same crystallization, than to mingle a deter- 
minate acid with the salt of which it forms a constituent part: results evidently 
very much opposed to the supposition of which we have spoken above. 
However, M. Beudant was desirous to see whether it would not turn out other- 
wise in the dry way, in as much as, from the beautiful experiment of M. Mit- 
cherlich, it is probable that more silicates are formed thus than in the wet way. 
He therefore exposed to a convenient heat, mixtures in definite proportions, and- 
others in which the substance which occupied the place of the acid, or that of the 
base, was superabundant. With the former he had perfect success; the others, 
on the contrary, and especially those in which the silex exceeded, did not produce 
one atom of the body which he expected to form ; but in its place there were two 
products, distinctly separated in the crucible, between which the elements had di- 
vided themselves, so that in each of them there were definite proportions. But 
