A, M. Mayer on measuring Electrical Conductivities. 307 
the converter as dark smoke, but as incandescent vapor having 
its characteristic spectrum. The lack of sufficient flame may, 
therefore, account for the disappearance of the manganese spec- 
trum. The Bessemer flame presents other problems, and opens 
an intensely interesting field for scientific investigation ; and by 
the use of more delicate instruments than have yet been em- 
ployed for this purpose, discoveries may be made which will 
throw new light upon the subject of spectrum analysis. 
Art. XXIX.—On a simple method of measuring Electrical Con- 
ductivities by means of two equal and opposed magneto-electric 
currents or waves ; by ALFRED M. Mayer, Ph.D. 
[Read before the Troy mecting of the American Association for the Advancement 
of Science.] 
portion of its ee Se projecting beyond a fixed stop (see fig. 2) ; 
over this free end of Pp 
the reverse of those of the other. The spirals are clamped 
together and their four terminal wires are carried vertically 
downward into four separate cavities containing mercury ; these 
mercury-cups are so connected with a reflecting-galvanometer 
