Intelligence and Miscellaneous Articles. 463 



with the nature of the gas, being as much more considerable as the 

 gas is a better conductor of electricity. 



In the same memoir, we next studied the effect of the magnet 

 upon a discbarge which takes place along the line joining its two 

 poles. In this case we observed, on the contrary, a very percep- 

 tible augmentation of the intensity of the current. We confined 

 ourselves to establishing that this diminution of resistance, occa- 

 sioned in the Geissler tube placed axially between the two magnetic 

 poles, is the more marked the better conductor the gas and the less 

 its pressure. With a view to complete our first observations, we have 

 resumed and varied this experiment. May we be permitted to ex- 

 plain here briefly, though they are still far from complete, the re- 

 sults to which our latest researches have conducted. 



Instead of arranging our electromagnet in the shape of a horse- 

 shoe as in our former experiments, with the two horizontal bobbins 

 in a line with each other and the two opposite magnetic poles, se- 

 parated by an interval of 10 centims., which compelled the Geissler 

 tube to be introduced into the cylindrical aperture pierced in the 

 axis of each of the two soft-iron cores, we here employed the elec- 

 tromagnet in a column, so as to cause only one of the magnetic 

 poles to act upon the discharge. The apparatus in which the dis- 

 charge took place (Greissler tube or a large bell) rested on the upper 

 extremity of the soft-iron cylinder, the line of the electrodes being 

 in the prolongation of the axis of the magnet. 



We commenced by operating with cylindrical Geissler tubes of 

 30 centims. length and 32 millims. breadth, presenting interior 

 electrodes of platinum wire. One of these tubes contains nitrogen, 

 the other hydrogen, both at a very low pressure, about 1 millim. or 

 even less — at least, judging from the appearance affected by the dis- 

 charge in their interior. The induction-current, furnished by a 

 Bnhmkorff machine of medium size excited by four of Grove's 

 couples, passed through the Geissler tube and then the derivation- 

 apparatus employed in our previous researches. It was on a very 

 small portion of the current, derived into a galvanometer placed far 

 enough from the magnet to be uninfluenced by it, that we observed 

 the variations of intensity of the discharge, according as it was or 

 was not submitted to the action of the magnet, which was excited 

 by 20, 25, 30, and sometimes even 40 Bunsen couples. 



Traversed by the discharge from the Euhmkorff machine, each 

 of the two Geissler tubes exhibits around the negative electrode a 

 beautiful blue aureola extending to the sides of the tube, beyond this 

 a long dark interval, and thence to the positive electrode streaks 

 wide apart. The appearance of this discharge is completely changed 

 as soon as it is submitted to the action of the magnet and when the 

 negative electrode is at the bottom or under the immediate action 

 of the magnetic pole. Indeed, as soon as magnetization commences, 

 the negative aureola, which, with a length of about 35 millims., oc- 

 cupied the whole diameter of the tube, is transformed into a cylinder 

 of only 8 or 9 millims. diameter, very luminous, extending to the 

 positive electrode, across the interval previously occupied by the 



