Prof. Gautier on recent Researches relating to Nebule. 101 
cent. The mineral called tetradymite, taking Berzelius’s analyses 
of that from Schoubkau as an example, has the following for- 
mula, (BiTe,)?+BiS,, and other analyses agree closely with 
this, Examples of a compound or complex mineral formed by 
the union of two simple ones are common; for instance, bro- 
myrite (Ag Br) and kerargyrite (Ag Cl) unite to form embolite 
(Ag Cl+AgBr); and others might be cited. It seems therefore 
probable that when sulphur is present in a tellurbismuth, it is due 
‘oan admixture of bismuth glance (BiS,), and that tetrady mite, 
like embolite, is formed by the union of two simple minerals ; 
in the case of tetradymite these minerals are tertellurid of bis- 
muth, BiTe,, and tersulphid of bismuth, BiS,, (bismuth glance, 
& mineral much resembling the other in its physical properties). 
The native tertellurid of bismuth in a pure state, has | 
observed only at Dahlonega, Ga., and the “Tellurium Mine,” 
luvanna Co., Va., and is up to this time at least, a mineral pe- 
culiar to the United States. 
.~4king this view of the subject, the American tertellurid of 
bismuth should be considered a new species, to which the term 
etradymite is hardly applicable. 
In conclusion I would call attention to the fact, that, although 
by artificial means bismuth and tellurium can be fused together 
In all Proportions, in their native combinations one equivalent 
of the former appears to be always united to three equivalents 
of the latter metal; the bornite of Brazil offers the only excep- 
tion to this rule and according to Damour’s analysis differs en- 
y from the other tellurbismuths. 
» Mass., May 20, 1862. 
— 
Art. XVII — Recent Researches relating to Nebule; by Prof. A, 
Gautier. (Translated for this Journal from the Bibliotheque 
Oniverselle, for Sept., 1862.) 
(We have translated Prof. Gautier’s article, both because it furnishes a 
Compact and clear account of the recent researches relating to nebula, 
and for the sake of showing our readers the esteem in which the labors of 
* Serge American astronomers are held abroad. We have taken 
the li tty to add foot notes on one or two points where some change 
“eemed desirable.—Eps. ] 
TuERE is no part of the vast field of practical astronomy 
Which does not require laborious investigation. I propose to 
Me general idea of those researches which relate to a very 
b 8¢ and curious class of celestial ne ska first specially studied 
Y the two illustrious astronomers erschel and Messier, and 
recently by Lord Rosse, by Fathers di Vico and Secchi, 
