in highly Rarefied Elastic Fluids. 



255 



could have no electrical communication except through the plati- 

 num wire soldered to the circumference of each and enclosed in a 

 glass tube. The free extremities of the two platinum wires could 

 be put into connexion respectively with the terminals of a galvano- 

 meter. The apparatus was so arranged that the two platinum disks 

 could be introduced into the stratified electric discharge, so as to 

 cut it transversely and to have their centres in the axis of the dis- 

 charge. They thus served the purpose of a shunt to lead off a part 

 of the current, and the intensity of this derived part, which is less 

 in proportion to the conductivity of the interval contained between 

 the extremities of the branch-circuit, was measured by the deflec- 

 tion of the needle of the galvanometer placed in communication 

 with the free ends of the platinum wires carrying the disks ; the 

 wires, as we have said, were surrounded by glass tubes through- 

 out that portion of their length which traversed the receiver 

 containing the rarefied gas, in order that they might remain 

 well insulated, and that the disks alone might be in contact with 

 the gaseous substance which transmitted the discharges. It was 

 now only needful to reverse the direction of these discharges, in 

 order that, without moving the platinum disks, they might be 

 either in the dark space near the negative electrode, or in the 

 luminous space near the positive electrode.. The apparatus was 

 moreover so constructed that they could be placed in other parts 

 of the electric jet. We may add that the electrodes between 

 which the electric jet passed were two platinum disks, each 5 

 centims. in diameter, placed parallel to each other at a distance 

 which could be varied from 50 to 80 centims., and that they were 

 consequently, like the small -disks which served to lead off the 

 derived current, perpendicular to the axis of the jet. 



The following are the results of some experiments made suc- 

 cessively with nitrogen and hydrogen : — 



Nitrogen or Atmospheric Air, 



Intensity of derived current. 



Pressure of the 



Platinum disks Platinum disks 



near the positivejnear the negative 



electrode. electrode. 



