356 M. E. Goldstein on Electric Discliarges 



ing as the position of the tube is equatorial or axial. One of 

 the two arms of this figure is always more or less narrow, 

 and pressed against the wall of the tube ; the other arm is 

 wide, and in the equatorial position spread out like a sail. This 

 sheet appears continuous if tlie discharges are not very strong; 

 if the discharges are strong, it breaks up into distinct magnetic 

 curves. If the discharges are very intense the two arms are 

 separated, and we have the appearance which I have described 

 in a former communication as the magnetic effect on '' thick 

 sparks"*. 



The inclined bridge between both arms of the figure appears 

 also in the form of a wide sheet made up of magnetic curves. 

 The narrow arm joins this bridge to the positive pole, the wide 

 arm to the negative pole. If the tube is shifted parallel to 

 itself, the position of the bridge shifts towards the other side. 



9. The phenomenon just described allows us to convince 

 ourselves that the magnet can set parts of the positive light 

 into magnetic curves. If the positive pole lies in the line 

 joining the poles of the meagnets, the positive light close to the 

 pole sets into the lines of magnetic force. I have also inves- 

 tigated the green light which appears on the glass under cer- 

 tain circumstances, chiefly round the negative electrode. 



10. 1 have found that this luminosity of the glass is rather 

 due to phosphorescence than to fluorescence, as it lasts a good 

 deal longer than the discharge. The colour of this light may 

 even change during its existence, as it does in a common 

 glass, from green towards a yellowish red. 



11. The negative light which produces this phosphorescence 

 is, as Ilittorf has already assumed, propagated in straight 

 lines which emanate from the electrode into the surrounding 

 space. I have been able to confirm this by many experiments. 

 There are, however, phenomena which distinguish this propa- 

 gation in straight lines from others which also take place in 

 straight hnes like that of hght. Hittorf has observed that a 

 body situated between an electrode which has been reduced 

 to a point, and the walls of the glass, throws a shadow on the 

 wail in the phosphorescent light. But even if the electrode 

 consists of a sheet of some extension, we can obtain well de- 

 fined, though not absolutely sharp shadows of bodies which 

 are not too far away from the electrode. A simple sheet of 

 light emanating from the electrode would only throw a hardly 

 visible penumbra on the Avail. 



Every surface-element of the negative pole, instead of ra- 

 diating equally towards all sides, only sends out a small cone 

 of light, the axis of which lies in a direction normal to the sur- 

 * Plnl. Mag. May 1875. 



