196 WEBER OX THE CONNEXION OP DIAMAGNETISM 



that together with these narrow convolutions, each spiral formed 

 two greater convolutions, which were traversed by the current 

 in an opposite direction, and which embraced an area equal to 

 that embraced by all the narrow convolutions taken together. In 

 accordance with the known laws of electro-magnetism, we could 

 here have no immediate action exerted by the current upon the 

 magnetometer, a conclusion capable of easy proof. The entire 

 action exhibited by the magnetometer was therefore due to the 

 magnetism of the iron alone, and may be determined with equal 

 sharpness and exactitude as that of permanent magnets, accord- 

 ing to the directions given by Gauss in the Intensitas, &c. It 

 is especially to be mentioned that the spirals made use of by 

 Miiller, Buff and Zamminer were shorter than the bars of iron 

 which they were used to magnetize. With Miiller this difference 

 was but trifling, for the iron bar projected only 15 millimetres 

 beyond the ends of the spiral. With Buff and Zamminer 

 it was however much greater, for here the ends of the largest 

 and thinnest bar projected 45 miUimetres beyond the two ends 

 of the spiral. The injurious influence of this was increased by 

 the circumstance that the length embraced within the spiral 

 amounted to only 110 millimetres, whereas in the case of Miiller 

 the enclosed length was 300 millimetres. This circumstance is 

 probably the chief cause of the divergence in the results arrived 

 at by these observers ; for it is manifest that the action of the 

 spiral upon the iron is greatest at the centre, decreasing towards 

 the ends, and that this decrease must, beyond the limits of the 

 spiral, be exceedingly speedy. Hence, although the action pro- 

 duced by the galvanic current upon the central portions of the 

 bar may have nearly attained its limit-value, it by no means 

 follows that this is the case with the portions without the 

 spiral. To effect this approximation at all points of the iron 

 bar simultaneously, in the following experiments a spiral was 

 made use of which was considerably longer than the bar of iron, 

 so that the force exerted by the spiral (whose diameter was very 

 small in comparison to its length) upon the ends of the bar 

 did not differ sensibly from that exerted upon its centre, by 

 which precaution alone secure results could be obtained. 



Without entering upon the details of these experiments, I 

 will here limit myself to a tabular statement of the results ob- 



