RECENT PROGRESS IN PHYSICS. 353 



3. Galvanic effects. 



4. Magnetization of steel. 



5. Physiological effects. 



6. Penetration of bad conductors, and 



7. Evolution of heat. 



The needle of a galvanometer inserted in the connecting wire of 

 he outer coatings is not affected when the inner coatings are brouo^ht 

 Into metallic contact with a white and loudly sounding spark, without 

 the interposition of a moist thread ; but it is sensibly affected when a 

 noist thread is introduced there. The magnetizing of a steel needle 

 placed in a spiral was produced with great effect in the first case, 

 iVithout interposition,) but feebly in the second case, (with inter- 

 oosition.^ 



I The contents of one of Dove's papers in Poggendorf's Annalen, 

 'LIV, 305,) bearing the title, " On the current induced in magnetiz- 

 ing iron by means of frictional electricity, 'i will have to be presented 

 later, because this subject is closely related to the corresponding 

 l^ffects of the galvanic current. 



I § 70. HankeVs researches on magnetizing steel needles hy the discharge 

 \parkof the electrical battery. — Hankel has published two large me- 

 fnoirs on this subject, (Pog. Ann., LXV, 537, LXIX, 321.) In the 

 idrst he speaks of Savary's observations, and then proceeds to the 

 ilescription of his own experiments, the resultsof which are as follows: 

 1. When the discharge stroke passes through a spiral in which a 

 iteel needle is placed, a certain minimum of charge is generally ne- 

 jessary to magnetize the needle. Calling the polarity which it receives 

 )y the discliarge stroke of this minimum, normal, the needle will be- 

 lome abnormally magnetic by gradually increasing discharges, and 

 ^gain normal by still stronger charges, &c. The abnormal magnet- 

 iism appears with strong charges of the battery, as the pieces of wire 

 introduced into the circuit of the battery are longer in proportion as 

 ihe charge is stronger. 



i When in addition to the spiral and the pieces of the conducting 

 iircuit remaining constant in all the experiments, an iron wire 34 

 jieet long and 0.1 line in diameter was introduced, abnormal magnet- 

 ism was obtained with a charge 70 (measured by sparks of the measur- 

 ing jar) ; on inserting 82 feet of the same wire a charge of 120 was 

 Required, and a wire of 154 feet required a charge of 160. 

 I 2. When a battery of more, and then one of fewer jars was used 

 ipith the same conducting circuit, the battery of the less number of 

 jars produced the abnormal period with a less charge. ' 



; An iron wire of 202 feet having been introduced, a charge of 20 

 ffith two jars produced abnormal magnetization, while by using 5 

 ars it was only obtained with a charge of 70, and with 9 jars, even 

 Ihe quantity of electricity 230, did not produce abnormal magnetiza- 

 ion. 



I If with gradually increasing charges, the change from normal to 

 .bnormal magnetization is not always obtained, these periods are 

 'levertheless not wholly wanting ; for an increase and decrease of the 

 Itrength of the normal magnetism is observed, and the minima of the 

 ' 23 s 



