600 SCIENTIFIC RECORD FOR 1882. 



November, II, i, 477) ; by G. Wiedemann {EJectroteclinisclie Zeitschrift, 

 July ; Phil. Mag., V, xiv, p. 258) ; and by Rayleigb {Phil. Mag., Novem- 

 ber, V, XIV, p. 329.) 



Naccari and Guglielmo bave studied tbe electromotive forces ot bat- 

 teries which are not constant, and find that the nature of the plate on 

 which the hydrogen is evolved affects the value of the electromotive 

 force of a single liquid cell ; and that the electromotive force of such a 

 couple varies always inversely to the intensity of the current, and that 

 this variation does not appear to be produced by the oxygen dissolved 

 or by the zinc sulphate produced. {II Nuovo Cimento, III, ix, p. 1G2 ; J. 

 Phys., November, II, i, p. 521.) 



Mazzotto has examined the constants of various cells, the internal 

 resistance being determined by Mance's method, and the electromotive 

 force being calculated from this and the current strength. He finds 

 that in all the batteries tested the electromotive force diminishes con- 

 tinuously when the current strength increases, and conversely. The 

 internal resistance is greater as the battery is longer in action and as 

 the current is weaker. {J. Phys., November, II, i, 522.) 



Minchin, in a paper on the determination of electromotive force in 

 absolute electrostatic measure, has discussed the theory of and given 

 the results obtained with his absolute sine electrometer (referred to 

 in this report a year ago). He finds, for example, the electromotive 

 force of a Daniell cell with his instrument to be 0.00352 absolute electro- 

 static unit ; while the value as obtained by Sir William Thomson, was 

 0.00374. {Nature, January, xxv, p. 278.) 



Rayleigh, in a paper read before the Physical Section of the British 

 Association upon the absolute measurement of electrical currents, said 

 that the measurement of current strength in absolute measure was 

 more difficult than that of resistance. All the methods hitherto em- 

 ployed require either accurate measurements of the horizontal intensity 

 of the earth's magnetism or of coils of small radius and many turns. 

 This latter is difficult to evaluate. Kohlrausch's method is free from 

 this objection, but it requires a knowledge of the moment of inertia, a 

 quantity not easy accurately to determine. Mascart's method is simple 

 to think about but not calculated to secure precise results. {Nature, 

 September, xxvi, p. 465.) 



With the aid of a Mascart electrometer, Berthelot has studied the 

 polarization of a zinc-carbon couple. When first set up, the electro- 

 motive force surpasses that of a zinc-platinum couple in the ratio 1 : 1.7(>, 

 and a Daniell cell in the ratio 1 : 1.29, or even 1: 1. 37. It falls, how- 

 ever, very rapidly on closed circuit, becoming equal to that of a Dan- 

 iell in a few minutes, and falling to 0.83 of a Daniell in a few hours. 

 After thirty-six hours it became only half that of the Daniell. If the 

 plates be now washed several times in water frequently renewed, they 

 give the original electromotive force again. {Ann. Chini. Phys., Sep- 

 tember, y, XXVII, p. 106.) 



