L. M. Cheesman—Measurement of Electric Currents. 117 
statement it appears that solid bitumen occurs in great abund- 
ance, filling aocieee formed cavities which in no oase pene- 
trates the roof above the mass, ‘‘ but was evidently injected from 
below.” Here the maltha accompanies the water of springs 
from deep-seated strata often in close proximity to active or 
extinct volcanic action of the mild forms observed as cap n 
mud volcanoes or salses. The great similarity ia cur- 
rence of intruded "as bitumens in Albania and ‘California 
is very remarkable. 
It should be borne in mind that while this subject is one of 
speculation, pure and simple, it is a subject that has its valu- 
able consideration outside the domain of scientific enquiry or 
curiosity, as affecting the sources and duration of supplies of 
petroleum, its profitable development and commercial perma- 
nence. If petroleum is the product of a purely chemical shat: 
we should not expect to find Paleozoic petroleums of a compo- 
sition corresponding with the simple animal and segembte 
Art. XVI.—On the Measurement of rey gare Pn ages 
Currents with the Galvanometer ;* by L. M. CHE 
Preliminary.—In view of the frequent use made of rapidly 
alternating electric currents in determining the resistance of 
liquids, ete., a more delicate instrument than the one we now 
have for such determinations has become a desideratum. At 
* From a paper by L. M. Cheesman, read before a = Academy of Sciences 
of Prussia by Professor von Helmholtz, July 13, 188 
