184 C. Bar us — Effect of Magnetization on the 



2/3Xl0 9 = 234 136 110 90 70 48 22 



<pXlO"= 30 50 65 80 105 150 240 



to which add the values on page 183. 



The accelerated rate of increase of <p with p as exhibited by 

 these data has suggested the remarks already made, viz : since <p 

 is independent of the sign of the current in the helix it is prob- 

 able that p may be taken sufficiently small to render these phe- 

 nomena practically available for the measurement of induced 

 or alternating currents. The actual deflection increases with 

 the length of the iron wire. It would be expedient therefore to 

 suspend a light mirror bifilarly from very long filaments of iron 

 and of glass or metal, surrounded by a long cylindrical helix.* 

 The rate of twist temporarily stored iu the soft iron filament is 

 the maximum within the elastic limits. I give the following 

 example of deflections produced by the current of an ordinary 

 induction coil, acting on a relatively thick and short iron wire.f 

 The currents are alternately off and on. The two series were 

 made about an hour apart. 



Nos. 5, 6; 2 / o=0-090 om ; Z=SO cm ; deflection = 



30 



75 



40 



80 



40 



83 



40 



<p:=20XlO' 



52 



85 



40 



75 



35 



73 



35 



g?=19X!0- 



In so thick a wire the heat effect of alternating magnetiza- 

 tions soon becomes apparent. The result is temporary diminu- 

 tion of the rigidity of the wire. Much better results are already 

 apparent when the above thin wires are used. For instance, 

 (same coil), 



Nos. 15, 16; 2 i o=0-034 cm ; Z=30 cm ; deflections= 



50 180 50 200 70 190 70; <p=65XlO- 6 



70 200 60 200 65 200 60; ^=69X10- 6 



Further discussion of these results (the errors of which are 

 largely due to the apparatus) is not now expedient. 



The values of <p in table 5 are means of five observations 

 with the circuit alternately made and broken. A small amount 

 of permanent detorsion is always imparted to the wire after 

 the magnetism has disappeared, as Wiedemann^: first pointed 



* It is needless to state that I am well aware of the difficulties here in the 

 way, difficulties which Wiedemann has so careiully digested. In my apparatus, 

 however, all pivot and pulley rotations are avoided. I have also repeated the 

 results relating to fine wires at length with very light mirrors, by which no 

 errors due to an asj^mmetrical mirror adjustments are encountered. The very 

 small couples which come into play in operating with filamentary wires often 

 make damping by submerged vanes objectionable. I have therefore often dis- 

 carded them. 



f The wire plates at my disposal were such that 2p = 0-02 was the smallest 

 diameter obtainable. But the above series of results are fully sufficient and suffi- 

 ciently in accordance to justify the inferences drawn. 



\ Wiedemann: Galvanismus, p. 689. 



