Intelligence and Miscellaneous Articles. 247 



adequate for the purpose of ascertaining extremely feeble induction- 

 currents through diamagnetic substances. Eor this I combine with 

 it a process of multiplication similar to Weber's, but with three 

 commutators. 



A commutator (I.) alternates in very rapid succession the direc- 

 tion of the current in A and B. A second commutator (II.), moved 

 by the same mechanism, turns the conduction of the spirals a and 

 b to the galvauometer in such wise that all the induction-actions of 

 the diamagnet which arise in a on the alternation of the principal 

 current, arrive in the same direction at the galvanometer. These 

 induction-shocks (10-12 per second) give, according to known laws, 

 a constant displacement from the position of rest. This enduring 

 deflection can be directly observed. In harmony with all the in- 

 vestigations hitherto made, it appears that the arising and vanishing 

 diamagnetism induces in neighbouring conductors currents opposite 

 in direction to those obtained by means of magnetic bodies. 



Observation becomes still more convenient and sensitive when 

 another, a special commutator (III.) is brought into the galvano- 

 meter-conduction, which the observer, after the known method of 

 multiplication, turns at the end of each oscillation until the ampli- 

 tude reaches its extreme value. Of course small deviations from 

 perfect compensation of the coils a and b must be determined by 

 comparing observations with and without a diamagnet, and taken 

 into account. In this way, with proportionally small spirals (A 

 and B 500 turns each ; a, b, and galvanometer each 1000), I ob- 

 tained, the galvanometer being moderately astatized, a constant 

 extreme amplitude of 15 scale-divisions by means of six Bunsen 

 cells and inside the induction-spiral a bundle of rods of bismuth of 

 200 grms. weight ; while a particle of fine iron wire weighing only 

 0*0044 grm. gave 556 scale-divisions in the opposite direction. With 

 very delicate astatizing a single Bunsen cell was sufficient, with the 

 above means, for the perception of the induction-current by the 

 diamagnetism of the bismuth. 



In this place I recommend also for similar observations a very 

 simple modification of the mirror-galvanometer, by which four 

 times instead of twice the angle of deflection is measured. Oppo- 

 site to the galvanometer-mirror a fixed horizontal strip of looking- 

 glass is placed, at a distance from 10 to 15 centims., and the tele- 

 scope and scale adjusted so that the rays of light meet the galvano- 

 meter-mirror twice before entering the telescope — which is easily 

 accomplished if the dimensions of the mirror are suitable. Prom 

 the reading s the deflection-angle a is found according to the for- 

 mula 



tana= , 



4<D+d) 



in which D and d denote the distances of the scale and the fixed 

 auxiliary mirror from the mirror of the galvanometer. This 



