HKB
all comparable with those derived from photographs; especially as regards the accurate size of the spots as compared with the diameter of the sun. And no doubt he is right.
"What, do I suppose, is the cause of these spots in the sun? Well, that is a very difficult question to answer. Changes are constantly going on at the sun's surface, or, I may rather say, in the sun's interior, and making themselves apparent at the surface. Sometimes they go on with enormous activity; at other times they are more quiet. They recur alternately in periods of seven or eight weeks, while these again are also subject to a period of about eleven years--that is, the short recurring outbursts go on for some years, when they attain a maximum, from which they go on decreasing. I may say that we are now (August 1883) at, or very near, a maximum epoch. There is no doubt that this period has an intimate connection with our auroral displays; but I don't think that the influence sun-spots have on light or heat is perceptible. Whatever influence they possess would be felt alike on the whole terrestrial globe. We have wet, dry, cold, and warm years, but they are never general. The kind of season which prevails in one country is often quite reversed in another perhaps in the adjacent one. Not so with our auroral displays. They are universal on both sides of the globe; and from pole to pole the magnetic needle trembles during their continuance. Some authorities are of opinion that these eleven-year cycles are subject to a larger cycle, but sun-spot observations have not existed long enough to determine this point. For myself, I have a great difficulty in forming an opinion. I have very little doubt that the spots are depressions on the surface of the sun. This is more apparent when the spot is on the limb. I have often seen the edge very rugged and uneven when groups of large spots were about to come round on the east side. I have communicated some of my observations to 'The Observatory,' the monthly review of astronomy, edited by Mr. Christie, now Astronomer Royal,[2] as well as to The Scotsmam, and some of our local papers.[3]
"I have also taken up the observation of variable stars in a limited portion of the heavens. That, and 'hunting for comets' is about all the real astronomical work that an amateur can do nowadays in our climate, with a three-inch telescope. I am greatly indebted to the Earl of Crawford and Balcarres, who regularly sends me circulars of all astronomical discoveries, both in this and foreign countries. I will give an instance of the usefulness of these circulars. On the morning of the 4th of October, 1880, a comet was discovered by Hartwig, of Strasburg, in the constellation of Corona. He telegraphed it to Dunecht Observatory, fifteen miles from Aberdeen. The circulars announcing the discovery were printed and despatched by post to various astronomers. My circular reached me by 7 P.M., and, the night being favourable, I directed my telescope upon the part of the heavens indicated, and found the comet almost at once--that is, within fifteen hours of the date of its discovery at Strasburg.
"In April, 1878, a large meteor was observed in broad daylight, passing from south to north, and falling it was supposed, about twenty miles south of Ballater. Mr. A. S. Herschel, Professor of Physics in the College of Science, 'Newcastle-on-Tyne, published a letter in The Scotsmam, intimating his desire to be informed of the particulars of the meteor's flight by those who had seen it. As I was one of those who had observed the splendid meteor flash northwards almost under the face of the bright sun (at 10.25 A.M.), I sent the Professor a full account of what I had seen, for which he professed his strong obligations. This led to a very pleasant correspondence with Professor Herschel. After this, I devoted considerable attention to meteors, and sent many contributions to 'The Observatory' on the subject.[4]