through Rarefied Gases. 413 



the chief tube. The following observation shows that this light 

 is not a stationary one, like the light of a flame or like the mag- 

 netic light, but it is light which passes to the end of the tube 

 and back again to form again a portion of the general electric 

 current. 



61. Amongst the tubes constructed by M. Geissler for the 

 sake of effect, there was a cylindrical one of about 35 centimetres 

 in length, and 3 to 4 centimetres in thickness. Inside this was a 

 narrow tube bent several times, its whole length exceeding a metre. 

 One end of this narrow tube carried a platinum electrode, and 

 was fused into the first end of the wider external tube. The 

 other and open extremity of the narrow tube terminated near the 

 end of the wdder tube, at a place where the latter was much con- 

 tracted. The wide tube, after being again widened, received the 

 second electrode. As the electric current was discharged out of 

 the narrower into the wider tube, only a portion of it passed, 

 through the contraction of the latter ; another portion was spread 

 out backwards in the wider tube, forming beautiful rings round 

 the narrower one. On laying the tube in an equatorial position 

 upon the magnet, the light became disposed about its upper and 

 under parts. The current descended from the opening of the 

 narrow tube, passed backwards along its lower side, and then 

 rose, proceeding to the upper side of the tube towards the con- 

 traction. On altering the direction of the current and inverting 

 the magnetic polarity, there resulted the modifications of the 

 phsenomena which were to be anticipated. It was remarkable 

 that, whatever might be the direction of the electric discharge, 

 magnetic light always occurred at the second end of the wider 

 tube. 



Deviation of the Electrical Light-currents by the approximation 

 of Conductors. 



62. A remarkable circumstance is the different kind of devia- 

 tion of the electrical light-current on bringing the hand or other 

 conductor into its neighbourhood. This deviation is very various, 

 according to the difi"erent nature of the ponderable substance in 

 the tubes : it is especially remarkable when the tubes contain 

 traces of fluoride of siliciura. 1 shall here describe an observa- 

 tion made by M. Geissler, in that gentleman's name. 



63. Amongst the diverse forms which M. Geissler has lately 

 given to his tubes, one form is especially remarkable, on account 

 of the varied nature of the pha;nomena which it ofiers. These 

 tubes, 50 to 70 centimetres in length, are composed of several 

 pieces : the middle piece has an ellipsoidal or cylindrical widen- 

 ing. The ends are composed of wider and shorter cylinders, 

 bearing spheres into which the platinum electrodes arc fused. 



