STRANGE NEWS ABOUT THE SOLAR PROMINENCES. 
57 
of motion (at that level) sufficient to carry it to a distance of 
350.000 miles from the sun’s surface if unretarded. But as 
the matter (on the hypothesis we are considering) did not 
reach this distance (250,000 miles from its starting place), hut, 
on the contrary, only traversed a distance of 100,000 miles 
before being reduced to rest, it is obvious that its initial velo- 
city (at level 100,000 miles) must have been greatly in excess 
of the velocity which, at that level, would correspond to an 
upward range of 350,000 miles in all. In other words, the 
hydrogen, when at a height of 100,000 miles, was travelling 
much faster than a projectile would cross that level if pro- 
jected in vacuo at a rate of 255 miles per second. So that leaving 
out of consideration all the retardation experienced by the 
hydrogen before it reached the level 100,000 miles, its motion 
at that level corresponded to an initial velocity much exceed- 
ing 255 miles per second. But, if the retardation was so con- 
siderable between the levels 100,000 miles and 200,000 miles, as 
to reduce the hydrogen to rest at the last-named level, whereas 
in vacuo it would have reached a level much exceeding 350,000 
miles, how much more effective must the retardation have 
been in the first 100,000 miles of the hydrogen’s upward 
course ? It is difficult to express how much greater must be 
the average density of the solar atmosphere between the pho- 
tosphere and a height of 100,000 miles, than between the 
height 100,000 miles and 200,000 miles ; but the disproportion 
must be enormous. Apart from this, the retardation being 
always proportioned to the velocity (though the law of this 
proportion is not known), would have been much more effective 
in the lower part of the hydrogen’s course, on this account 
alone. We have, then, this important conclusion (on the hypo- 
thesis we are dealing with), that after traversing a range of 
100.000 miles from the sun's surface under the action of a 
retardation enormously exceeding that operating on the hydro- 
gen in the observed part of its flight , the uprushing hydrogen 
still retained a velocity far exceeding that due to a velocity of 
255 miles per second at the sun's surface in the case of a pro- 
jectile in vacuo . 
But we have now to consider towards which hypothesis we 
should lean, or rather which cause we should consider as chiefly 
operative. 
In the first place, it is obvious that we cannot dismiss the 
hypothesis of retardation entirely, for glowing hydrogen travel- 
ling through an atmosphere even of extreme tenuity at an 
average rate of 167 miles per second must needs be enormously 
retarded. But I think that, apart from this, we cannot for a 
moment accept the belief that the hydrogen wisps which Pro- 
fessor Young watched as they slowly vanished at a height of 
