The sun's spots, which we will next refer to, are deep, relatively dark, but in fact extremely bright depressions in the photosphere. "Many spots are of enormous size" (see article, "Sun"); "one had a diameter exceeding fifty thousand miles, and many far larger than this have been seen. The spots are not scattered over the whole surface of the sun, but are for the most part confined to two belts between latitude five degrees and thirty degrees, on either side of the solar equator. An equatorial zone six degrees wide is almost entirely free from spots.... The inclination of the solar equator is about seven degrees.... The spots on the sun usually have a dark central region called the umbra, within which is a still darker part called the nucleus, while around this there is a fringe of fainter shade than the umbra, called the penumbra. Although the umbra and nucleus appear dark, however, it is not to be supposed that they are really dark; ... though the nucleus looks perfectly black by contrast with the general surface, it shines in reality with a light unbearably brilliant when viewed alone, while his thermal measurements show that the heat from the nucleus is even greater proportionately than the light, and not very greatly below the heat of the surrounding surface.... The recognition of a nucleus within the umbra would seem to indicate that a third cloud layer (besides the outer or photosphere and a darker cloud layer beneath) exists within the second or internal layer of Herschel's theory. But the observations of Professor Langley show that most probably all the features of the solar photosphere yet observed are phenomena of cloud envelopes, since he has been able to recognize cloud forms at one level floating over cloud forms at a lower level, while even in the (relatively) darkest depths of the nucleus clouds are still to be perceived, though so deep down that their outlines can be barely discerned." Professor Ball says of the heat-wave of 1892, "As to the activity of the sun during the past summer, a very striking communication has recently been made by one of the most rising American astronomers, Mr. George E. Hale, of Chicago. He has invented an ingenious apparatus for photographing on the same plate at one exposure both the bright spots and the protuberances of the sun.... On the 15th of July a photograph of the sun showed a large spot. Another photograph taken in a few minutes exhibited a bright band; twenty-seven minutes later a further exposure displayed an outburst of brilliant faculæ all over the spot. At the end of an hour the faculæ had all vanished and the spot was restored to its original condition. It was not a mere coincidence that our magnetic observatories exhibited considerable disturbances the next day, and that brilliant auroras were noted." Carrington's observations have shown that spots in different solar latitudes travel at different rates. "Taking two parts of the visible solar surface in the same