248 Intelligence and Miscellaneous Articles. 



arrangement is recommended in those cases where the measurement 

 of the angle cannot be carried to a greater nicety by increasing the 

 magnifying-power of the telescope or by large scale-distances. 



In the above-described process for observing diamagnetism, 

 beside the slight action to be measured, an incomparably greater 

 one, the direct induction of the spirals, must be compensated. It 

 is therefore a principal thing with the apparatus to be able to ensure 

 the compensation and preserve it unaltered. This is only possible 

 when the system of commutators (I. and II.) satisfies certain con- 

 ditions in its construction, to be more particularly described in 

 another place, and when the spirals are well insulated, so that in 

 their windings no secondary closings variable with the temperature 

 shall exist. JSTow these conditions, as we learn from observation, 

 can be fulfilled with very remarkable completeness ; and hence, in 

 my institute, diamagnetic measurements will be carried out accord- 

 ing to this method with more powerful spirals. 



I have also executed another (and, so far as I know, undescribed) 

 form of differential inductor, with which the induction produced 

 by the arising and vanishing magnetism upon the principal current 

 is observed. Let four branches A, B, C, D be, after the manner 

 of "Wheatstone's combination, united so that the principal current 

 divides into two branches A-j-B and C + D, and let the bridge 

 together with the galvanometer be inserted between the angle-points 

 A B and C D. Let the branches A and C contain each a single 

 spiral of great magnetizing force. Now let the action of the sta- 

 tionary current upon the galvanometer be compensated by resist- 

 ances in B and D. The action, in general still present, of the extra 

 currents at the closing and opening of the circuit is compensated 

 separately, by micrometrically displacing fine iron rodlets in the less 

 powerful spiral until the galvanometer shows neither stationary nor 

 momentary deflections. Induction, however, is immediately again 

 produced by the opening and closing when a feebly magnetic body 

 is placed in the other spiral ; this can, as before, be multiplied and 

 measured. 



It is true that this last method is far more difficult in practice ; 

 but it might be suitable for the investigation of certain reactions 

 on current-electricity. Thus, for example, by it one might study 

 the question whether the rotation of the polarization of light in 

 magnetic or diamagnetic bodies under the influence of the current 

 reacts on the current, which, with present views on electricity and 

 the luminiferous aether, is not improbable. It was intended obser- 

 vations of this kind that induced me to make the above-described 

 preliminary experiments on electrical induction-currents through 

 diamagnetic bodies. — Kaiserliche Akademie der Wissenschaften in 

 Wien, Sitzung der math.-nat. Classe, January 21, 1875. 



