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POPULAR SCIENCE REVIEW. 
poles there is no vast depression to cross ; the molecules in their passage 
encounter the resistance of a continuous layer, and cannot acquire the same 
velocity as at the poles. Hence the light -will mostly he produced at the 
poles, and especially at the pole actually deprived of solar light. 
What is the Cause of Solar Scoria ? — This important question has been 
taken up by M. Faye, who answers M. Zollner’s views at length in the 
“ Comptes Rendus ” of the French Academy. He says that the spots are 
scoriae produced by local cooling of the incandescent liquid which forms the 
solar globe. Their relatively low temperature gives rise to currents analo- 
gous to those about our coasts and islands ; only in the sun they do not 
alternate. The lower currents flow perpendicularly to the sides of the islet 
from within outwards ; the upper from without inwards. Hence a con- 
tinual series of vertical movements, the horizontal axes of which are 
tangential to the contours of the scoriae. Naturally the solar radiation is 
partly suppressed by such an islet ; and if the temperature sinks to the 
point of condensation of vapours in the atmosphere, clouds are formed, jsvhose 
figure depends on the upper currents flowing from all parts towards the 
vertical axis of the islet. They will especially be produced towards the 
central part, and the scoriae will appear as a dark nucleus with its enceinte of 
penumbra. This local cooling, and the descending movement of the atmo- 
sphere towards the interior, will explain the depression observed at the dark 
nucleus of spots, and the effects of perspective as they approach the edge of 
the disc. If the ascending currents outside of the islet are strong they will 
leap up and give the appearance of ordinaiy protuberances. As to the 
eruptive protuberances, they are due to a local diminution of atmospheric 
pressure. The gases included and compressed, or simply dissolved in the 
liquid mass, escape like the gas-bubbles in seltzer water when the cork is 
drawn. The movements of spots are explained by “ trade-winds ” from the 
poles to the equator. The component of this action in the direction of the 
parallels diminishes the velocity of rotation, and retards the spots more in 
regions near the pole than at the equator, where the action is nil. Large 
scoriae often break up and form several spots, the incandescent ocean ap- 
pearing from below. Remarking on this theory, M. Faye points out that the 
spots on nearing the edge ought, according to it, to show a projection at the 
side of the sort of vase of which the scoriae form the bottom ; but there is 
nought of this, and the orifice becomes even with the edge of the disc. The 
depth of the spots has been measured, and found on an average three to four 
seconds. Everything indicates that the spots are cavities and not projec- 
tions. On the other hand, the theory is more closely related to his (M. 
Faye’s) own than P. Secchi’s ; both supposing a circulation and down rush 
of hydrogen ; the axis, however, being, according to. the author, vertical. 
And it is also preferable to the eruption theory in that it agrees with laws 
of movement of the spots, one of these being that each spot follows the 
movement of the parallel in which it is, and if it passes into another parallel 
takes the movement of that. But then one would suppose that the islets 
of scoriae would be driven by the trade-winds supposed, towards the equa- 
tor (like our ships). There is no such movement, and one even finds neigh- 
bouring spots which have limited movements in opposite directions, one 
towards the equator, the other towards the poles. The elliptic oscillation, 
