\^Q PHENOMENA ACCOMPANYING 



while the raoro contracted, with less capacity of conduction, grow warm, and 

 become luminoud, even when it is the same discharge which traverses them. 

 We shuiild here expect a phenomenon exactly analogous to that which is pro- 

 duced when we place in the circuit of a voltaic jiilc a chain formed of alternate 

 wiresofplatina and silver, having the same length and diameter; although they 

 both tran.<mit the same current, the wires of platina, offering most resistance, 

 grow hot, and become even incandescent, while those of silver, being better 

 conductors, remain cold and opaque. 



To demonstrate that in fact the space remaining opaque offers less resistance 

 to the transmission of electricity in the stratified column than the luminous part 

 of that column, I have arranged two small disks of })latina, 7™™ in diameter, 

 each attached by a point in its circumference to the cud of a wire of platina, 

 enclosed in a tube of glass, in such a way as to be kept parallel to one another 

 at a distance of three centimetres. The two disks are connected in a solid 

 manner, though very carefully isolated, and without any possible electric com- 

 munication except by means of the wires of platina soldered to their circumfer- 

 ence, and enclosed in a tube of glass. The free extremities of the two wires of 

 platina can be respectively placed in communication Avith those of the wire of a 

 galvanometer. The apparatus is arranged in such manner that the two disks 

 of platina may be introduced into the stratified electric stream so as to cut it 

 transversely, and to have their centres situated in the very axis of the stream. 

 They thus serve as sounds destined for the derivation of a part of the current, 

 and the intensity of that derived portion, which is so much less as the conduc- 

 tibility of the interval of derivation is greater, is measured by the deviation of 

 »he needle of the galvanometer put in communication with the free extremities 

 of the platina wires which support the disks ; these wires, as has been said, are 

 themselves enclosed in tubes of glass where they traverse the recipient which 

 contains the rarefied gas, with a view to their remaining well isolated, and that 

 the disks alone may be in contact with the gaseous substance which transmits 

 the discharges. Now, it suffices to change the direction of these discharges in 

 order that the sounds, without being displaced, shall be immersed either in the 

 obscure space near the negative electrode, or in the luminous space Rear the 

 positive one. The apparatus is, moreover, so contrived that the sounds may be 

 placed in other portions of the current. It is proper to add, that the electrodes 

 between which the electric stream passes are two disks of platina, each five cen- 

 timetres in diameter, placed parallel to one another at a distance which may 

 vary from forty to thirty centimetres, and consequently, like the little disks 

 serving as sounds, perpendicular to the axis of the stream. 



Tlu; following are some experiments made successively with nitrogen and 

 hydrogen : 



NITROGEN, OR ATMOSPHKRIC AIR. 

 Pressure of the gas. Intensity of the derived current. 



Sounds near thepositive electrode. Sounds near the negative electrode. 



6""" 70° 18° 



4™"^ 40° 8° 



2™"^ , 18° 3° 



HYDROGEN. 



IS'"'^ 90° 90° 



e""'^ 82° 65° 



4'"'" 52° ... 2° 



^"" \\ 35°[[[[[[[]]" ..].][['.]'.[ 0° 



We see from these tables that the intensity of the derived current diminishes 

 with the pressure, although the transmitted current be much stronger, which 

 Bhows with what rapidity the resistance of the gas diminishes in proportion as 

 ito rarefaction increases. But at the same time the diminution of the derived 



