Chemical Science^ 431 



cated by the occurrence of a certain quantity of pyrites and blend. 

 May one not be led to conclude, that the silver was originally 

 united with the sulphur, but that, by the effect of terrestrial mag- 

 netism, it has been carried towards the copper and zinc, or, in 

 other words, that the vein occurring in the direction of the mag- 

 netic meridian, the magnetic force has produced a similar effect in 

 it to that occurring with a platina wire in the voltaic circuit? — Ann. 

 de Chimiey xxxviii. 201. 



4. On the Magnetism of Galvanometer Wires^ and of Metals gene- 

 rally. — Every electrician is acquainted with the beautifully delicate 

 galvanometer, contrived by M. Nobili, in which two magnetic 

 needles nearly neutralize each other's tendency to point in obe- 

 dience to the earth's magnetism, and are conjointly acted upon by 

 a wire conducting voltaic electricity, so as by their deflection to in- 

 dicate the presence and force of the current in the wire. M. Nobili 

 has often observed that the needle of his instrument, when out of 

 use, instead of pointing to zero, and taking up a position parallel 

 to the conducting wires, deviated to the right or the left, sometimes 

 by as much as 16° or 20°. This deviation only occurred in those 

 instruments, which were so thoroughly neutralized, that the earth 

 possessed scarcely any directive influence over them. On examin- 

 ing the wires of the galvanometer no iron could be detected in 

 them, and, afler much research, M. Nobili concluded that the effect 

 was due to an attraction exerted by the copper wires of the instru- 

 ment, analogous in its nature to that observed by M. Arago be- 

 tween the magnetic needle and various metals*. Six or seven 

 copper wires, about one hundredth of an inch in diameter, being 

 united and placed about the twenty-fiflh of an inch from the needles 

 in the plane of their motion, drew them from 15° to 20° from their 

 place of rest, when uninfluenced. The same effect took place with 

 platina wires, but more weakly ; silver wires were found to be 

 almost without action on the galvanometer needles. . By using sil- 

 ver wires M. Nobili was able to construct a galvanometer, far more 

 sensible than with wires of any other metals, in consequence of its 

 freedom from interfering action. This instrument he intends 

 shortly to describe. — Bib. Univ. 1818, p. 79. 



5. Early History of Electro-Magneizsm.'-^ln the year 1801 

 Gautherot brought two fine pianoforte strings in contact, one with 

 the upper and the other with the lower, end of the pile, keeping 

 the extremities fluttering in the air. When these ends touched each 

 other, he says {Ann. de Chimie, xxxix. 209,) ** A very decisive ad- 

 hension took place ; they seemed united as by a magnetic power, 

 which was so strong, that he could move the united wires in every 

 direction to a distance of some centimetres." Thus it may be seen 

 that, in the investigation of nature, a few detached- observations are 



♦ Accofdiug to M. Arago, this is rather a repulsion than an atlrac'tibri.— -Ed. 



2G2 ' ' 



