upon the Electrical Discharge in Rarejied Gases. 129 



become the liglit-pole, in the neighbourhood of which they did 

 not extend as far as the sides of the tube (fig. 11). 



32. On both hnibs of the electro-magnet the two heavy 

 armatures were again placed (fig. 12) with their rounded ends 

 turned to one another. Iq the first instance, the tube was so 

 placed upon these, in an axial position, that the point of the 

 platinum wire which still served as the warmth-pole was situated 

 nearly above the point of maximum action. The diffused light 

 surrounding the platinum wire became, in consequence of the 

 magnetic action, concentrated to an arched disc of violet light, 

 which stood in an axial position upon the two armatures and 

 was bordered approximately by two concentric circular arcs 

 whose centre coincided with the middle point between the 

 higher surfaces of the two armatures. In the inner arc, which 

 touched the extremity of the platinum wire and formed almost 

 a semicircle, light was concentrated in the form of a bright 

 narrow strip, while the remainder of the space, 8 to 9 millims. 

 broad, between the two concentric arcs was more feebly, though 

 for the most part uniformly, illuminated. Towards the end of 

 the tube alone, beneath the platinum wire, the light increased 

 in brightness. The wire itself, as is always the case, remained 

 constantly surrounded by a finely stratified envelope of light. 

 In this case the feebler illumination is also bordered with perfect 

 sharpness by the higher arc, which terminates upon the platinum 

 wire just where it is fused into the bulb. A narrow dark 

 interval separated the light around the warmth-pole from the 

 remaining light of the tube, which had retained its stratification. 

 The form of the layer only followed to some extent that of the 

 border in the neighbourhood of the dark interval. Moreover, 

 the stratified light no longer filled the whole interior space of 

 the tube : it had concenti'ated itself in a horizontal direction on 

 one or other side, in the manner of the previously described 

 horizontal aberration (14), in consequence of the armature 

 placed beneath it. On inverting the magnetic polarity the 

 phsenomenon gradually disappeared, but reappeared again slowly 

 in precisely the same form, with the exception, which we need 

 not further consider, that the stratified light was driven into 

 the opposite side of the tube in a horizontal position, the side 

 view of the tube remaining the same on turning it round. 



33. If the tube (fig. 13), still remaining in an axial position, 

 was so moved endways that the place where it rested upon the 

 armatures approaclicd the light-pole, the appearance was quite 

 changed. TJie two arcs of light, which were before circular and 

 which bordered the ring in which the atmosphere of light had 

 become concentrated around the warmth-pole, assumed the form 

 of magnetic curves. 



Phil. May, S. 4. Vol. 16. No. 105, Aug, 1858. K 



