ye 
814 B. V. Marsh on the Aurora, 
In an aurora the centre of the corona being the vanishing 
point of the nearly parallel streamers which compose it, it 18 
evident that a streamer having its base exactly in this centre 
of the observer (at A, or B, fig. 1) being a continuation of its axis. 
But it is found that this line always coincides with the direction 
of the axis of the dipping needle, at whatever place the obser- 
vation is made, and, since the position of the dipping needle at 
as the appearances in the electric discharge in vacuo are wi 
different at the positive and negative terminals. 
It is true that we have succeeded in tracing the streamers only 
five or six hundred miles, out of the many thousands they must 
traverse to reach their destination in the southern hemisphere, but 
their illumination even thus far beyond the supposed limits of the 
atmosphere is probably due in part to particles of matter carried 
from the arch, just as portions of the platinum wire were con- 
veyed by the currents to the surface 3 the glass in the experi- 
ments of Prof. Pliicker—and the invisibility of the streamers 
beyond this point may result from their great distance from the 
observer combined with the greater diffusion of the current and 
the absence of matter to be illuminated.* 
* The experiment of Prof. Pliicker shows that electric currents have a powerful 
tendency to transport portions of the electrode, the cohesion of even so hard a sub- 
two hemispheres, although simultaneous, are not identical, Pn 
ely 
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