306 STEATIFIED DISCHARGE. SECT. XXIX. 



lastly the indication of a polished one. When the air-pump was 

 filled with attenuated olefiant gas the rings were precisely the 

 same with those seen in thin plates ; hence the effect is the same 

 as that produced by the interference of light. In these experi- 

 ments the luminous appearance extended from three quarters of 

 an inch to an inch round the point of the needle or wire. 



When the silver plate was connected with the negative pole of 

 the battery a polished point appeared upon it opposite the needle, 

 surrounded by a dusky ill-defined areola of a brown colour tinged 

 with purple when viewed in one direction, and greenish- white 

 when seen in another. 



In the present year Mr. Gassiot, Vice-President of the Eoyal 

 Society, has shown that the stratified character of the electric 

 discharge is remarkably developed in the torrecelian vacuum. 

 Among the various experiments made by that gentleman two 

 may be selected as strongly illustrative of this new and singular 

 property of electrical light. 



In a closed glass tube about an inch internal diameter and 33 

 inches long, in which a vacuum had been made, two platinum 

 wires were hermetically sealed, 32 inches apart, and connected 

 with the poles of an inductive battery. The luminous appear- 

 ance at the two poles was very different when electricity passed 

 through the wires. A glow surrounded the negative pole, and in 

 close approximation to the glow a well-defined dark space appeared, 

 while from the positive pole or wire the light proceeded in a 

 stream ; but unless the charge be great or the tube short, the 

 stream will not extend to the black band, which is totally dif- 

 ferent from the intervening space. When discharges of elec- 

 tricity were sent through this vacuum tube a series of bands or 

 stratifications were formed which were concave towards the posi- 

 tive pole ; and as in the changes in making and breaking the 

 circuit the electricity emanates from the different terminals or 

 wires, their concavities were in opposite directions. 



When instead of platinum wires narrow tinfoil coatings were 

 placed round the exterior of the glass tube and connected with 

 the wires of the battery, brilliant stratifications filled the interior 

 of the tube between the foil coatings, but no dark band appeared. 

 At present Mr. Gassiot is inclined to believe that the dark band is 

 due to interference ; but that the stratifications arise from pulsa- 

 tions or impulses of a force acting in a highly attenuated but 



