632 PROCEEDINGS OP THE AMERICAN ACADEMY. 



luminous condition of ionization pervading the space between the poles 

 of a battery in a wide tube at a comparatively high pressure of the 

 containing gas, perhaps 3 centimeters. The positive carriers are not 

 restrained or held back by the swifter moving negative carriers, which 

 cannot manifest their energy in a limited free path. On a sudden 

 increase of pressure luminous clouds emerge from the anode. This 

 phenomenon seems to indicate a greater proportional falling off in the 

 energy of the negative carriers and a manifestation of superior energy 

 of the positive carriers. The cloud of collision between the two moves 

 slowly to the negative pole, the conductivity of the gas changing under 

 the difference of potential to which the tube is subjected. Two lumi- 

 nous clouds can be formed by a suitable change of pressure in the tube ; 

 a change of pressure easily produced by condenser discharges in a side 

 tube. These clouds, after the cessation of the condenser discharges, travel 

 slowly to the negative pole in the tube, and coalesce before they disappear 

 in this pole. We seem to have here a picture of the relative energy of 

 the positive and negative carriers with the war of collision between them 

 evidenced by the slow moving luminous clouds. The forms of these 

 slow moving luminous effects are perfectly represented by the illustra- 

 tions in Professor Rhigi's memoir. It is noteworthy that such slow 

 moving electrical clouds can be produced by a steady discharge from a 

 storage battery of ten thousand cells as well as with a powerful dis- 

 charge from a large condenser through a water resistance, as in the case 

 of Rhigi's experiments. 



The form of the electrodes is of considerable importance. If the 

 positive terminal is an aluminum plate of comparatively large diam- 

 eter, four centimeters, and the negative terminal a point, the luminous 

 masses retreat to the positive pole instead of moving to the negative pole 

 on an increase of pressure. The surface density on the positive plate 

 does not seem sufficient to force a volume ionization through the increase 

 in the volume of the gas. 



On the contrary, when the positive terminal is a point and the nega- 

 tive terminal the plane, an increase of pressure, with strong currents, 

 causes a slow movement of the luminous masses to the negative pole. 



A constriction in the glass tube results, in the formation in the con- 

 striction, of a fixed luminous mass which acts as a cathode. The posi- 

 tion of a side entrance to the tube leading to the pump does not seem to 

 have any influence on the position of the luminous masses. Perhaps 

 the most interesting case of slowly moving electric luminous discharges 

 is that of the very slow retreat of the positive column when the anode is 



