1881.] 



On Stratified Discharges. 



387 



potash in connexion with the tube). It may be added that when, as is 

 sometimes the case, through greater exhaustion, the striae became 

 feebler in illumination and less compact in appearance, the shadows 

 cast by them lost proportionally in sharpness of definition and in 

 completeness of extinction of the phosphorescent light. 



The reason for not extending the tin-foil beyond the column of striae 

 is, that when this is done the negative discharge from inside the strip 

 combines with that going on in the main dark space behind the anchored 

 striae in such a manner as to shorten the column by the length of the 

 strip. When this takes place, as is often, although not always the 

 case, the experiment is frustrated. 



The brilliancy and definition of the phosphorescent rings may be 

 increased by inserting a small Leyden jar in the circuit, care being 

 taken that the jar shall discharge itself completely each time. If this 

 is not the case, the main discharge is followed by subsidiary discharges, 

 which tend to blur the effect. The angle of dispersion may be increased, 

 or rather supplemented, by placing more than one strip on the tube, 

 distant from one another by an angle of 90° or 120°. By this means 

 the rings may be made to comprise the entire circumference of the 

 tube. 



It should be here mentioned that if the striated column be carefully 

 examined at the moment when the external discharge passes, it will be 

 noticed that the entire column (or more strictly speaking the part of 

 it lying between the positive terminal and the end of the tin-foil nearest 

 to the positive terminal) undergoes a slight displacement. This dis- 

 placement amounts usually to half the distance between two striae. 

 The actual shadows cast in the green phosphorescence are those due 

 to the displaced striae, as may be easily verified. 



It thus appears that the striae are competent to cast shadows in the 

 radiant showers issuing from the inside of the tube adjacent to the tin- 

 foil, which part acts as a negative terminal. Many experiments have 

 contributed to show that these radiant showers, although accompani- 

 ments of the discharge, are not carriers of the discharge ; and that, 

 having once issued from their source, they continue their own course 

 irrespective of that of the discharge proper. They are in fact material 

 showers, and, although not improbably charged with electricity, yet 

 their ulterior course does not appear to depend on their electrical 

 condition. Under these circumstances the most probable explanation 

 of the phenomena above described appears to be that the showers are 

 arrested by material obstacles in the shape of striae ; and consequently 

 if that be the case, we here have an experimental proof that the striae 

 represent local aggregations of matter, and not merely special electrical 

 conditions of the gas. 



