52 
fmall degree of expanfion to which they 
are liable when heated. 
Mr. HaTcuHerTT, at the fame meeting 
of the fociety; communicated fome expe- 
yiments on a mineral fubftance formerly 
fuppofed to be zeolite, with fome remarks 
on two fpecies of uran-glimmer, by the 
Rev. W. Grecor. This mineval is 
foutid in Stenna Gwyn, Cornwall, the 
principal produétion of which is the com- 
pound fuiphuret of tin, copper, and iron. 
‘There.are two fpecies of this mineral, 
-affuming a marked difference in external 
character; the firf? and moft common con- 
fits of an affemblage of minute cryftals, 
which are attached to quartz cryftals in 
tufts, which diverge from the point of ad- 
herence, as from acentre. Thefe tufts 
vary, as to the number of cryttals of 
which they are compofed, and are light 
and delicate in the forms which they af. 
fume, or they are grouped together ac- 
cording to a variety of degrees of proxi- 
mity and compactnefs. Sometimes they 
fill the whole-cavity of a ftone, with little 
or no interruption ; in other fpecimens 
they are feen partially fpreading over the 
fides and pointed’ pyramids of quartz cry- 
ftals. In fome cales thefe grouped tufts 
adhere very pertinacioufiy to the ftone 
wh:ch bears them, in others they are eafily 
feparable, in comparatively large pieces, 
from the quariz, the imprefled form of 
which the pieces, thus feparated retain. 
The furtace of thefe which was in imme- 
diate contaét with the quartz, exhibits 
the feveral minute cryftals of which the 
mafs contiits, matted together in various 
direétions. 
Thefe cryfalline afflemblages are, in ge- 
Neral, white; a nearer inipeétion fhews 
that the individual cryffals are tran{parent. 
Sometimes they are of a yellowith hue. 
The fize of the cryflals varies confiderably 
in different {pecimens ; but by the help of 
a powerful microfcope, they appear to 
confit of four-fided prifms; the {eétion 
exh:bits a rhomboidal, approaching to an 
elliptical, figure. | 
Imbedded among thefe cryftals two fpe- 
cies of cryftalline jamine are frequen:ly 
difgoverable ; the one confiding of paral- 
Jelopipedon plates with truncated’angles, 
applied to each other, of a green colour 
of various tints, from the emerald to the 
apple green; the other fpecies, coniifting 
of an aflemblage of {quare plates which 
vary in thicknefs. The angles of the fe- 
veral {quare Jamming are not aiways coin- 
cident. They are of a bright wax yellow, 
the fides of the largeft of them is about 
one-fourth of an inch. This lalt ipecies 
4 
Proceedings of Learned Societies. 
[Feb. 1, 
is frequently found adhering to the fides 
ef quzertz cryftals, in the cavities of gra- 
nite. 
The other fpecies of this mineral con- 
fits of an affemblage of cryftals clofely 
compacted in the form of mammiullary 
protuberances, of the fize of imal: peas, 
connected with each other. A ftratum of 
thefe about one eighth of an inch thick is 
fpread upon a layer of quartz, in the cavt- 
tics or fiflures of a frecies of compact 
granite. he ftrize of which thefe mam- 
mille cenfift diverge from a centre like 
zeolite. Some of the individual — ftrie 
overtop their fellows, in thefle globular af. 
fernblages, and evidently aflume, on their 
projecting po'nts, a cryftallized form. 
Such being the outline of Mr. Gregor’s 
def{cription, he next proceeds to derail the 
experiments very circumitantially. In thefe 
we cannot follow him; they wiii however 
he found highly deferving the attention of 
the chemift. In fpeaking cf the uran- 
gliromer, he fays, if he is not miflaken in 
the ‘ubttance, he has dere&ed the oxyde 
of lead, lime, and filica in it, which have 
not hitherto been confidered as ingredients 
of that fofil. The green cryftals differ 
in no refpect from the yellow, except in 
containing 2 little of theoxyde of copper. 
-PHILOSOPHICAL SOCIETY: oF 
: MANCHESTER. 
Vi% Datton, who is the conftant 
contributor to this literary and phi- 
Jofophical alfociation, has laid before it 
the refuit of an experimental enquiry into 
the proportion of the feveral gafes, or 
elatic fluids, conftituting the atmofphere. 
The cbjeéts of this enquiry are, 1. To 
de‘ermine the weight of each figple at- 
mofphere abitractedly 5 or, in other words, 
what part of the weight of the whole 
compound atmoiphere is due to azote, 
what to oxygen, &c. 2. To determine 
the relative weights of the different gafes 
in a given volume of atmofpheric air, 
fuch as it is at.the earth’s furface. 3. To 
invefiigate the proportions of the gales to 
each other, {uch as they ought to be tound 
at different elevations above the earth’s 
furface. To thofe who confider the at- 
moiphere as 2 chemical comvound, thefe 
threy objeGis are, in fact, bur one; but 
thofe who think with Mr. -Dalton that 
the elaftic power of each particle is con- 
fined to thofe of its own kind, and confe- 
quent’ y that the fo:ce of fuch fluid, re- 
tained in a given veffel, or gravitating, is 
the fame in‘a feparate as ina mixed ftate, 
depending upon its proper denfity, and 
temperature, will fee that they are equally 
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