JPeirce and Willson — Resistance of Batteries, etc. 465 



lar condition of their surfaces induced by rolling, two bars 

 from the same steel, one rolled and the other pressed, were 

 magnetized and then measured. The ratio of the specific mag- 

 netism of pressed to rolled was as 9 to 5, the rolled having the 

 smaller amount. The existing difference, in this case, is prob- 

 ably owing to a difference in hardness, rather than to any 

 molecular condition of the surfaces. 



The specific magnetisms of all the bars are small when com- 

 pared with good steel magnets. Kohlrausch says that good 

 magnets, of common form, should have #=40. The bar of 

 ordinary tool steel, however, retained but 7*46. Still it was 

 soft, and by tempering would doubtless have doubled this 

 value. 



If forged nickel and tungsten can be made to maintain a 

 specific magnetism of 10, it will form a useful addition to the 

 resources of physical laboratories. From the high polish 

 of which it is susceptible and its freedom from damaging 

 atmospheric influences, it will be most happily suited for the 

 manufacture of mirror magnets where magnetic damping is to 

 be employed. 



Jefferson Physical Laboratory. 



Aet. LYII. — Note on the Measurement of the Internal Resist- 

 ance of Batteries ; by B. O. Peirce and K. W. Willson. 



That galvanic cells, even under constant temperature condi- 

 tions, have no fixed internal resistance in the sense that a cop- 

 per wire has resistance, but that what we call the internal 

 resistance of a battery varies somewhat with the strength of 

 the current which is passing through the battery, is well known. 



Asa consequence of this variableness the value of the resist- 

 ance of even a so-called nonpolarisable cell, as determined by 

 any of the older methods, depends upon the resistances of the 

 outside circuits used in making the measurement. 



By the use of alternating currents,* however, it is possible to 

 get a value for the resistance of a battery, which remains con- 

 stant even though the resistance in the bridge and the intensity 

 of the current sent interruptedly through the primary coil of 

 the inductive apparatus be made to vary between rather wide 

 limits. 



Some time ago we had occasion to measure the quantity of 

 electricity which passed through the circuit when the poles of 

 a battery were connected by a conductor of moderate resist- 



*F. Kohlrausch, Pogg. Ann Jubelband, p. 220, 1874. Pogg. Ann., cliv. p. 1, 

 1875. Wied. Ann., vi, p. 1, 1879. Wied. Ann., xi, p. 653, 1880. 



