H. Haug on the Electro-motive Force, etc. 381 
scribed. ‘T'o do this requires a little dexterity; the diameter of 
the paper must be six or seven times that of the mouth of the 
funnel, it must be folded across in two rectangular directions in 
the ordinary way, then opened and reversed and from opposite 
points in the edges folded some distance past the middle. The 
funnel is then passed into it and the edges are passed round 
the neck of the funnel, the muslin is next placed over the pa- 
per and the whole is secured round the neck with cord. 
Art. Ll.—Ezperiments on the Electro-motive Force and the Re- 
sistance of a Galvanic Circuit; by HERMANN Have. 
constants I used Ohm’s method. A single galvanic cell was, by 
means of short, thick copper wires, connected with a tangent 
compass and a rheochord. The tangent compass was 0: 
gendorff’s construction, the needle suspended by a hair, and 
modified according to Gaugain, thus securing the proportion- 
ality between the intensity and the tangent. The rheochord 
was of thin platinum wire, of Poggendorft’s construction, mod- 
ified by Dubois-Reymond. Both instruments were made by the 
best artists in Germany. ; 
The law of the maximum of the effect of a galvanic battery 
requires both the internal and the external resistances to be the 
8a important reasons, which, however, have no 
ords. 
rom a careful study of the problem of ety application 
of the electro-magnetism as motive power, | have become con- 
Vinced that it is merely a question of economy—economy in 
any material to be consumed, as well as economy in power to 
Am. Jocr. Sct.—Szconp Srxses, Vou. XLII, No. 126.—Nov., 1866. 
49 
