156 DOVK ON THE ELECnilCITY OF INDUCTION. 



contrary proceeded from the filled spiral. In this form there- 

 fore the previously non-magnetic brass became magnetic. 



These experiments were now extended to antimony, lead, bis- 

 muth, tin, zinc and mercury. The insulation of the mercury 

 was effected by enclosing it in glass tubes sealed at both ends ; 

 the wires of the other metals were covered with shell-lac. The 

 copper was free from iron, according to the analysis of M. Henry 

 Rose. The lead contained a very slight trace of iron ; tin, anti- 

 mony and bismuth however more ; the zinc, examined by Dr. 

 Marchand, was chemically pure. I shall repeat these experi- 

 ments with some metals which I have since obtained in a per- 

 fectly pure state. 



The thickness of the wires was as follows : — Copper 0"''75, 

 tin l"''10, lead 0"'-80, zinc 0"'-60, brass 0"'-75, antimony 2"'-80, 

 bismuth 2"'"80 ; the mercury was contained in common ther- 

 mometer tubes. In the experiments the same kind of sew- 

 ing-needles (darning-needles) were always employed, and the 

 electric battery always received the same charge by means 

 of a unit-jar. If the compensation of the empty spirals was 

 not complete, it could always be effected by slightly altering 

 the position of the interior spiral towards the outer, or it was 

 established previously by the insertion of brass wires. The ex- 

 periments showed a very appreciable amount of magnetism with 

 copper, quite as much with tin, mercury, antimony and bismuth, 

 less with zinc, and very little with lead. A tube of brass dimi- 

 nishes the action of its spiral, — acts therefore in an unmagnetic 

 manner. A tube of German silver, as also drawn tubes of tin 

 and of lead, had a powerful magnetic action, even more powerful 

 than bundles of tin and lead wires. It is therefore probable 

 that in drawing these soft metals into tubes they become covered 

 with a thin film of iron. 



The positive result obtained with mercury is for this reason 

 of importance, that no possible admixture of iron could result 

 from drawing. In a former paragraph (53) alloys of iron have 

 been mentioned, which in the form of rods, tested in the same 

 manner, show themselves unmagnetic; the admixture of iron 

 cannot therefore, as such, determine the result. The magnetism 

 of these metals however compared with that of iron is so very 

 weak, that a single iron wire of the same thickness is capable of 

 overpowering in its magnetizing action a whole bundle of wires 



