PHYSICS. 279 



Becquerel has piiblislied an extended memoir on the magnetic ])roi)- 

 erties of nickel and cobalt compared with those of iron, using the oscil- 

 lation method, the differential method, and the electromagnetic-balance 

 metliod, for comparison, confining himself to the magnetism developed 

 by induction, and not the magnetism which remains permanent. The 

 author's most important conclusion is that for very feeble intensities, 

 under conditions very tar from saturation, or \yith substances in which 

 the magnetic particles are sufflciently removed, so as not to react the 

 one upon the other, the effects developed in the molecules of nickel and 

 of iron at the ordinary ttmperature appear to lie very near each other. — 

 {Ann. Chim. Phys., V, xvi, 227, February, 1879.) 



Hodges has contrived a new instrument for determining the inclination 

 of the needle, founded on the fact that the magnetic polarity of a bar 

 of soft iron is greatest when the bar lies in the line of the dip. In place 

 of a single bar, however, the author uses two, joined to each other at 

 right angles. When the two branches make equal angles with the line 

 of dip, the ends next the junction are of op])osite jjolarity ; and if similar, 

 will neutralize one another so that a needle suspended near them will 

 remain unaffected. The results on trial were very accordant under dif- 

 ferent conditions. — (Aw. J. ^ci., Ill, xvii, 145, February, 1879.) 



Rowland and Jacques have determined the diamagnetic contents of 

 bismuth and calc-spar in absolute measure, the former contributing the 

 theory, and the latter making the measurements. These latter consisted 

 of two : 1st, the determination in absolute measure of the magnetic 

 potential of the field used ; and, 2d, the determination of the time of 

 vibration and the other constants of the little bars of the substances when 

 suspended in this field. The diamagnetic constant of bismuth along the 

 axis was found to be —.000000012554 ; and for calc-spar —.0000000379:50, 

 in absolute measure. — {Am. J. iSci., Ill, xviii, 3G0, November, 1879.) 



2. Electromotors. 



Iloorweg has investigated the conditions of the production of elec- 

 tricity in the voltaic cell, and has advanced a thermic theory of its origin. 

 The following are his conclusions : 1st. Wherever two conductors arc in 

 contact, the heat movement has the production of electricity as a coiise 

 quence ; hence a constant electric difference exists between the bodies. 

 2d. Whenever the sum of the diiferences of potential existing in a cir- 

 cuitis different from zero, a permanent current is produced. 3d. This cur- 

 rent absorbs heat at certain of the points of contact and evolves it at others. 

 4th. All voltaic currents are thermo-currents. 5th. All chemical actions 

 in the cell and in apparatus for electrolytic decomposition are a conse 

 quence of the passage of the current. — {Ann. Phys. Chem., II, ix,552, ISSO; 

 J. Phjs., ix, 352, October, 1880.) 



Varenne has studied the phenomenon of the passivity of iron in nitric 

 acid as when employed as the positive plate of a Grove battery or the 

 positive electrode of a voltameter cell containing nitric acid. He con- 



