SCIENTIFIC SUMMARY. 
91 
MINERALOGY. 
Amblygonite. — The new mineral species, triploidite, described by Brush 
and Dana, is shown by them to be isomorphous with wagnerite, and closely 
related in composition to triplite. These three minerals have respectively the 
formulae (Mn, Fe) P 2 0 8 + (Mn, Fe) (0 Ii) 2 , Mg 2 P 2 0 8 + Mg F 2 and (Fe, 
Mn) 2 P 2 0 8 + (Fe, Mn) F 2 . From a comparison of these formulae it is 
argued that the relation between the minerals requires the assumption that 
the hydroxyl in triploidite must play the same part as the fluorine in the 
other two. In a paper on the chemical composition of amblygonite, by 
Samuel L. Penfield ( Amer . Jour. Sc., 1879, xviii. 295), the writer 
endeavours to show that in this mineral also the hydroxyl group is isomor- 
phous with fluorine, and that in chemical composition the original ambly- 
gonite does not differ from the American and Montebras varieties, which 
have been called hebronite. He also shows from the results of his ana- 
lysis, that a new and more simple formula than any previously accepted 
must be taken to represent its composition. The specimens examined are 
three from the Maine localities, from Branchville, Connecticut, two varieties 
from Montebras, and one from Penig, Saxony. All the specimens gave 
numbers approaching closely to the ratio 1 : 1 : 1 : 1 ; hence he proposes the 
formula Al 2 P 2 0 8 + 2 E (0 H, F), or \ j + { & \° 0 1 . as the 
true formula for all varieties of the mineral. Des Cloizeaux, from a difference 
of optical characters made out by him, has divided the mineral into two 
species : the original amblygonite, including the specimens for Penig, Saxony, 
and from Montebras, France ; and a second species, for which he proposes 
the name of montebrasite, the hebronite of Von Kobell, including all the 
other localities. Owing to the close identity in chemical composition, it seems 
that a slight variation in optical properties is hardly sufficient ground for 
dividing the mineral into two species ; and it is proposed that the old name 
of amblygonite should be retained, and that the varieties be included in it. 
PHYSICS. 
Photometric Researches on Coloured Flames form the subject of an impor- 
tant communication by M. Gouy to the Annales de Chimie et de Physique. 
In an introduction he gives a summary of what has been done in this depart- 
ment since the work of Bouguer, in 1729. His photometer — those of Rom- 
ford, of Foucault, and of Bunsen, the double refraction instrument of Arago, 
that by polarised light of Becquerel — are adverted to, all of which are exclu- 
sively confined to white light. The first prismatic photometer seems due to 
M. Gouy, and a very similar instrument to Vierordt. The latter consists of 
a spectroscope with two continuous slits, the breadth of which can be varied 
by means of a micrometer screw. The spectra being adjusted to equal inten- 
sity, the screw gives the relative breadth of the slits, and, consequently, the 
comparative brightness of the sources of light. Monsieur Gouy has success- 
fully employed two photometers. The former acts by throwing on the slit 
