172 The American Naturalist. February, 
Three fragments of powellite have been obtained by Koenig and Hub- 
bard” from the south Hecla copper mine in Houghton Co., Mich. The 
mineral has a density of 4.349. Its composition was found to be: 
MoO, WO, CaO MgO _ FeO, 
SiO, Cu Total 
67.84 1.65 27.30 .16 96 1 
52 tr = 99.43 
Native lead is reported by Kempton” as occurring’ in thin scales and 
pellets, some of which approach rectangular forms, in a gangue of 
pyroxene of a pale green color. It is associated with iron oxides and 
calcite. The location given is near Saric, Sonora, Mexico. 
Methods and Instruments.—Federow” in a recent article elab- 
orates a new universal method for the measurement of crystals, sug- 
gests a new system for crystallographic nomenclature and illustrates a 
new method of projecting crystal planes, and determining by graphical 
means their symbols. The universal goniometer used in his investiga- 
tions is described at length and pictured in detail. The author illus- 
trates also the application of his method to studies in optical erystallo- 
graphy. He describes two models of universal microscope stages, 
constructed for the purpose of enabling the observer to revolve the 
object under investigation in two directions. The plagioclases ane 
studied and it is shown that the labor of determining their nature 8 
much reduced by the method of work suggested by the author. 
paper is an important one and and one well worthy of close study. 
Czapski” suggests the use of the iris diaphragm between a condense 
of moderate strength and the stage of the microscope for the rapid 
interchange of parallel and converged light, and also the use of the 
same appliance in the ocular tube of the instrument for the isolation of 
the axial figures of very small crystals. 
G. Friedel” gives a new method for determining the value of the 
double refraction in thin sections of minerals that seems to be simple 
in its application. s 
Goldschmidt” and Jolles” discuss two proposed methods for projec 
tion of crystal forms. Jolles article is illustrated by five plates and 
sixty figures. 
*Ib., XLVI, 1893, p. 356. 
Science, June 23, 1893, p. 345. 
*Zeits. f. Kryst., XXI, p.574and XXII, p. 229. 
Ib. XXII, p. 158. 
*Bull. Soc. Min. Franc., XVI, p. 19. 
sib., XXII, p. 20. 
*Ib., XXII, p. 1. 
