March 31, 1910] 



NA TURE 



143 



two discharges in the shape of narrow triangles the bases 

 of which are close to a dark space separating the glow 

 surrounding them from a central rosette. The pointed 

 ends are close to a second dark space, and are terminated 

 by tuft discharges. These appearances show only imper- 

 fectly in the reproduction, but are exceedingly definite on 

 the original negatives. The remarkable feature is the 

 very sharp and well-defined edges which these triangles 

 possess. It is suggested that there may be a connection 



It is noteworthy that the positive figures in various gases 

 present very few differences from each other. 



When a small metallic triangle placed on the sensitive 

 film forms the electrode, some striking differences are 

 obtained according as it is made the positive or the negative 

 terminal. When it is positive the ramifications start in 

 the main from the corners (Fig. 3) ; on the other hand, 



Fig. I. — Discharge at a pressure of about 17 cm, 



between these and the phenomena of electrostriction, but 

 so far no definite theory has been formulated. In very 

 many cases there is visible a dark continuation of these 

 squirts on the side of their bases, which suggests that the 

 effects seen represent a part only of the electrical effects 

 taking place. The shape of the squirts suggests that in 

 one region they experience a pressure from the disturb- 

 ance which creates the luminous glow through which they 

 stretch, and that this pressure is replaced by a tension 

 as soon as the second dark space is passed. The luminous 



Fig. 3. — Positive ramifications from comers of triangular electrode. 



when it is negative a preference is shown to leave at 

 right angles to the edges (Fig. 4). 



Throughout these descriptions it has been assumed that 

 the discharges leave the electrode. It must be admitted 

 that at present there is no proof that thfe streamers do 

 not represent currents that advance toward the electrodes. 



For some further details, as well as for numerous other 



Fig. 2. — Negative! figure in coal-gas at ordinary pressure. 



glow bordered by the two dark spaces suggests a single 

 stria as seen in a vacuum tube ; the phenomena of ionisa- 

 tion in the two cases may be similar. 



When the gas in which the plate is immersed is changed 

 the effects obtained change also. Each gas produces a 

 negative figure characteristic of itself. The triangular 

 squirts above referred to are given by air alone. The 

 negative figure in coal-gas at ordinary pressure is shown 

 in Fig. 2. The figure in nitrogen is also very singular. 1 



NO. 2IOQ, VOL. 83J 



Fig. 4. — Negative streamers exhibiting a preference to leave the triangle 

 at rigtit angles to edges. 



reproductions, reference must be made to the paper in the 

 Journal of the Rontgen Society from which the figures 

 illustrating this article have been selected. Perhaps it 

 should be added that these are photographic positives from 

 the original photographic negatives. 



Alfred W. Porter. 



