Intelligence and Miscellaneous Articles, 



317 



Variation of Resistance ivith Temperature. 



Steel 



Iron 



Tin 



Thallium 



Cadmium. 



Zinc 



Lead 



Aluminium 



Silver 



Magnesium 



Copper 



Gold 



Silver jflft) 



Palladium 



Platinum 



Brass 



Aluminium bronze 

 German silver 

 Mercury 



B*= 



B (1 + 0- 

 (1 + 

 (1 + 



(i+o- 



(1 + 0' 

 (1+0 

 (1 + 

 (1+0 

 (1 + 

 (1 + 

 (1 + 

 (1 + 

 (1-0 



(i+o 



(1 + 



(i+o 

 (i+o 



(1 + 



(i+o 



'004978*+ 0' 

 004516* + 0' 

 004028* + 0- 

 004125*+O 

 004264* + 

 004192*+O 

 003954*+ 0' 

 003876*+ 0' 

 003972* + 0' 

 003870*+0' 

 •003637* + 

 '003678*+ 

 •003522* + 

 ■002787*+0 

 ■002454* + 

 '001599*) 

 •001020*) 

 •000356*) 

 •000882*+ 



000007351* 2 ) 

 000005828* 2 ) 

 000005826* 2 ) 

 000003488* 2 ) 

 000001765* 2 ) 

 000001481* 2 ) 

 000001430* 2 ) 

 000001320* 2 ) 

 000000687* 2 ) 

 000000863* 2 ) 

 •000000587* 2 ) 

 ■000000426* 2 ) 

 •000000667* 2 ) 

 •000000611* 2 ) 

 •000000594* 2 ) 



000001140* 2 ). 



Comptes Mendus deVAcademie des Sciences, vol. lxxvi. pp. 342-346. 



ON THE CONDITIONS REQUISITE FOR THE MAXIMUM OF RESIST- 

 ANCE OF GALVANOMETERS. BY M. TH. DU MONCEL. 



Mr. Schwendler, and several other physicists previously, have 

 found that, for a galvanometer to be in the best possible conditions 

 of sensitiveness in relation to a circuit of given resistance, the re- 

 sistance of its magnetizing helix must be equal to that of the exterior 

 circuit in communication with it. Several experiments having de- 

 monstrated to me that the sensibility increases with the length of 

 the helix-wire, under other conditions than those thus indicated, I 

 submitted to calculation the galvanometric effects with regard to a 

 circuit of given resistance ; and I have ascertained that those con- 

 ditions of sensitiveness demand a considerably greater length of 

 wire in the multiplier than that which corresponds to the resistance 

 of the exterior circuit. 



To demonstrate the law which he had laid down, Schwendler en- 

 deavours to calculate the number * of the turns of the helix of the 

 multiplier as a function of the space C occupied by the helix-wire, 

 and also as a function of the resistance H of the latter. Designa- 



C 



ting by s the section of this wire, * becomes equal to — , and the 



C* . s 



length II of the helix equal to — ; which supposes wrongly that 



the resistance is proportional to the number of the spiral turns, and 

 inversely as the section of the wire. 



According to these data, it would result from the combination of 



