112 Scientific Intelligence. q 
contain the pigment. They are distinguished by the large proportion of 
pith, which begins a short distance from the point and very soon constit 
tutes almost the entire thickness of the hair. The pith consists of large 
polygonal cells. Thus the opposite electrical state of the two ends may 
possibly be caused by the prevalence of the cortical fibre in the upper 
and of the pithy substance in the lower part, this pith being filled with 
air ce.ls. 
rof. Kobell considers a closer ey of ee — prope . 
_ erystals, induced by friction, very des rable ; he nds 
deer-skin stretched over a wooden eats asa a im ie xe = 
latter with other fibre. Employing this rabber, (and in case of thin 
laminz, as those of mica, merely the dry fingers,) and soe examining 
the electricity with the “ Gemsbart,” he has made the following electrical 
groups of minerals: 
I Groupe. Good insulators 
When rubbed attract the indicator. ; 
i De. Electro-positive insulators 
repel th indicator 
: 
Calcite, aragonite, fluor, barytes, Ais rite, gypsum, anhydrite, oii 
quartz, topaz, emerald, grossular, idocrase, kyanite, orthoclase, albite, to a 
maline, axinite, zircon, muscovite (Grafton, N. H.), spinel, alum, wa i. 
t, ete. oo 
2. Ey, bia ahi, ala insulators i 
repel the — indicator. oe 
Tale, sulphur, orpiment, amber, asphaltum. 
Group. Good conductors. : | 
Do not attract the serene and are coated by a oaon frags when 7 
immersed with a zinc holder lution of sulph. ¢ : : 
gold, vo Line) pyrites, ibiplaess stiitoopy tite: eobaltin ne, amt i 
magnet 
Il ee Bad conductors and bad insulator as compared with 
Group II. 
Do not attract the indicator, or only feebly, and are not coated with 
so, eae if treated as in Group IL 
ond, celestine, almandine, melanite, biotite and hinge: ride 
lite any clinochlore, pennine, analcime, sphene, stibnite, hemati 
linite, zinkenite, jamesonite, chromic iron, red copper, pea et = 
ganite, psilomelane, hausmannite. 
To determine the kind of electricity of Groups IT and ITI, the minerals 
must be insulated; this is readily done by fastening them with wax o® 
the end of a glass ‘rod of sufficient diameter, taking care e face to 
be rubbed projects far enough beyond the wax, to prevent ney rubl 
from coming in contact with the latter. a 
_ In the examination of small sasiali st it is often convenient to mount 
them on shape rated insulating them to thes merannen 7 the mi 
the crystal with Etiek, when Ww fit be - 
not loose its sey. : 
