RECENT PROGRESS IN PHYSICS. S57 



18 a long wire introduced into the circuit is extended in a straight 

 line or wound into a spiral, will be considered helow under No 6. 



4. It appears in general, as Hankel infers from his experiments, 

 ;hat with coarse needles the phenomena do not change ; the anomalous 

 periods occur only with stronger charges, and also appear to have lost 

 n strength. 



5. New experiments on the influence of the surface of the battery, 

 iorresponding to the previous ones, indicated that a diminution of the 

 lurface brought about the anomalous periods with decreasing charges, 

 )ut so shortened them .that, with a certain size of the battery, they 

 ;eased to appear as abnormal magnetization ; weak and strong normal 

 )eriod8 only were then observed. 



6. Besides the short insertion, with which the results in fig. 69 were 

 )btained, Hankel made experiments with inserted copperwires extended 

 n a straight line 0.23 millimetre diameter^ and varying between 0.375 

 md 96.4 metres in length. The curves 1 and 2, fig. 70, represent 

 he results which he obtained with the wires 12 and then 96.4 metres 

 ong. These curves seem to indicate that with longer insertions the 

 eparate small periods disappear, until at last only a large normal pe- 

 iod is observed with stronger magnetism, after which follows a very 

 )road negative period, (from 30 to 100,) in which, however, very weak 

 nagnetism is observed. 



With reference to the disappearance of the smaller periods, these 

 jxperiments do not admit, in my opinion, of any certain conclusion, 

 because the charge of the battery was increased from 5 to 5 for the 

 onger insertions, and from 2 to 2 for the medium, while they increased 

 [nly by 1 in the shortest. Where is the guarantee that in the longer 

 *^ires single periods are not passed over ? Hankel preserves silence 

 n this point. 



In relation to the influence of the coils, Hankel compares the result 

 epresented by the second curve of fig. 70 with those which are given by 

 03 metres of the same wire wound into 70 coils. While, with straight 

 /ires, a normal period extends to 30, and is then followed by a long 

 legative weak one, he observed, with coiled wires, 3 normal and 3 ab- 

 ormal })eriods. 



When 26 metres of a very thick (30.76 square millimetres in sec- 

 ion) quadrangular copper wire were inserted, no change was seen in 

 he succession of the periods, but they were generally feebler. When, 

 b addition, 113 metres of a round (1.3 millimetre) wire were inserted, 

 jtretclied in a straight line, the results represented in the third curve 

 |f fig. 70 were obtained. Nearly all reversions disappeared^ the needles 

 leemed but i'eebly magnetic. 



When 94 metres of the thick wire were coiled into a spiral and 

 pserted in the circuit, the results presented in the fourth curve of 

 ig. 70 were obtained. The enfeebling of the magnetism appeared 

 .ere in the thick coiled wires still more strikingly than in that ex- 

 pended at length. 



The influence of the coiling upon the thick and the thin copjier wires is 

 •vidently very different ; yet, says Hankel, (page 336 of his 2d Memoir,) 

 he influence is the same in both cases. The discussion, by means of 

 f/hich he seeks to prove this, is incomprehensible to me ; indeed, I 

 annot call Hankel's reasoning in general clear and precise. 



