240 Intelligence and Miscellaneous Articles, 



the polar extremities of all the tubes in contact with them : bat 

 these polar extremities cannot develop a magnetism greater than 

 that which they possess, and that only on those atoms of the 

 shields with which they are in contact; so that the magnetism 

 of the atoms situated on the other side of the shields (that is, at 

 the outside) will be very feeble, in consequence even of the thick- 

 ness of the latter. 



"Moreover, as the free extremities of the tubes of which each 

 core consists have each of them the same magnetic pole, on 

 uniting them to one another by a round shield of iron, between 

 these poles reactions are developed which diminish the magnetic 

 force of the system, just as happens in bundles formed of perma- 

 nent magnets." — CompUs Rendus de VAcademie des Sciences, Feb. 8, 

 1875, vol. lxxx. pp. 382-384. 



ON THE EXPERIMENTAL DETERMINATION OF DIAMAGNETISM BY 

 ITS ELECTRICAL INDUCTIVE ACTION. BY PROF. A. TOEPLER, 

 OF GRATZ. 



As is well known, Faraday and Weber have shown that cliamag- 

 netic bodies, when brought nearer to or moved further from a closed 

 spiral in a powerful magnetic field, generate induction-currents. 

 These certainly very feeble currents produced by the motion of the 

 diamagnet have even been made use of by Weber in order, by means 

 of a very sensitive apparatus, to compare the polarity of bismuth 

 with that of iron. 



The electrical-induction currents, however, can be observed and 

 measured without moving the diamagnet, by means of the diamag- 

 netism which is produced and vanishes — whereby the process is in 

 many respects simplified. I use for this purpose a differential in- 

 ductor with a system of commutators, in the following manner : — 



Let two spirals (A and B) of thick wire be inserted one behind 

 the other in the circuit of a series of constant intensity, and two 

 induction- spirals (a and b) nearly identical in constitution placed 

 in their cavities. Let the latter be likewise one behind the other", 

 but closed at opposite ends by a galvanometer. At the opening 

 and closing of the principal circuit the galvanometer is acted on by 

 only the difference of the two inductions ; and this difference is 

 quite eliminated by adding to the more feebly acting induction- 

 spiral (for instance, b) a small auxiliary spiral, which is inserted 

 with it in the galvanometer-circuit, and shifted by a micrometer- 

 screw towards the principal spiral B until the galvanometric effect 

 of the closing and opening vanishes even with a principal current 

 of great intensity. If now a magnetic or diamagnetic body be 

 placed in the middle of the other coil (a), the galvanometer again 

 gives, on the closing and opening of the principal circuit, the induc- 

 tion of the moment which is produced and vanishes. 



But this method (which, besides, was in like manner recommended 

 by Dove for feebly magnetic bodies such as nickel &c.) is quite in- 



