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the more frequent the spots. If we made a white globe to represent the sun, and made a black dot on it for every spot during a number of years, the dotting would make the globe look as represented in the figure.

Collections of numerous small spots brighter than the photosphere in general are frequently seen on the sun. These are often seen in the neighbourhood of a spot, and occur most frequently in the regions of greater spot frequency, but are not entirely confined to those regions. They are, however, rare near the poles of the sun.

That the spots and faculæ proceed from some one general cause has been brought out by the spectro-heliograph, an instrument devised by Professor George E. Hale for taking photographs of the sun by the light of a single ray of the spectrum, that emitted by calcium, for example. The effect is the same as if we should look at the sun through a glass which would allow the rays of calcium vapour to pass, but would absorb all the others. We should then see the calcium light of the sun and no other.

When the sun is photographed by calcium light with this instrument, the result is wonderful. The sun-spot regions are now seen to be brighter than the others, and faculæ are found on every part of the sun. We thus learn that eruptions of gas, of which calcium is the best marked ingredient, are taking place all the time; but they are more numerous in the sun-spot zones than else-