362 Proceedings of the British Association. 



variation of the needle in different parts of the globe, and de- 

 monstrated that there are two magnetic poles in each hemis- 

 phere. He exhibited maps of the variation at different dates, 

 and shewed that the line of no dip was not a great circle, but 

 inflected. He noticed the excursion of Hansteen to determine 

 the magnetic poles and variation in Siberia, the observations of 

 Captain Ross and others ; and concluded by remarking the ab- 

 sence of any data for determining the position of the southern 

 pole. 



15. Professor Wheatstone examined with a prism the line of 

 light formed by the voltaic spark between charcoal points. The 

 spectrum was complete without interruption, but marked by 

 certain lines of more intense brightness. With the electric 

 light from a surface of mercury, a few very bright lines of defi- 

 nite colour appeared separated by wide dark intervals. The 

 same light from different metallic surfaces gave similarly inter- 

 rupted spectra ; the divisions being distributed in a peculiar 

 manner in the spectra for each metal. In alloys and compounds 

 of different metals, the lines peculiar to each wire were com- 

 pounded. The voltaic light from a surface of mercury, and of 

 other metals in succession, gave analogous results. At different 

 points of the connecting wire the light appeared of different co- 

 lour ; that colour was found marked with a peculiarly bright 

 line in the corresponding spectrum. High characteristics afford 

 the means of distinguishing the different metals, and to deter- 

 mine the origin of the electric light in different cases. The 

 light from combustion of metals gave uninterrupted spectra ; 

 thus shewing, that voltaic light is not related to combustion. 

 The light of the electric spark from contact of different metals 

 gives similar light and dark spaces to those in the voltaic. Mr 

 Wheatstone applies these results to the theories of electric light, 

 and thinks they point out the volatilization of ponderable mat- 

 ter from the conductors, as the most probable hypothesis. 



16. The Rev. Mr M'Gauley exhibited and explained a new 

 principle, consisting in the application of magnetism as a mov- 

 ing power. The apparatus consists of two powerful electro- 

 magnets, so arranged that the contact is alternately changed 

 from one pole to the other, and the poles of the magnet thus re- 

 versed. This produces an alternate motion in the bar connect- 



