FEB. 18, 1894.
FEB. 19, 1894.
X.—Photographs of the Sun taken at the Royal Observatory, Greenwich, Shewing Sunspots.
Attracted little attention,
This brief announcement is all that the discoverer says upon the subject; and it is perhaps not remarkable that it attracted very little attention, especially when we remember that it related to a matter which the astronomical world had agreed to put aside as unprofitable and not worth attention. Next year, in giving his usual paper on the spots for 1844 he recurs to the subject in the following sentence: “The periodicity of spots of about ten years which was indicated in my summary published last year, is confirmed by this year’s observations.” I have added in brackets to the table above reproduced the numbers for 1844 subsequently given, and it will be seen how nearly they might have been predicted.
Still the subject attracted little attention. Turning over the leaves of the journal at random, I came across the annual report of the Astronomer Royal of England, printed at length. But in it there is no reference to this discovery, which opened up a line of work now strongly represented in the annual programme of the Royal Observatory at Greenwich. Mr. Johnson remarks that the only person who had taken it up was Julius Schmidt, who then resided near Hamburg.until eight years later. But Schwabe went on patiently accumulating facts; and in 1851 the great Von Humboldt in the third volume of his Cosmos, drew attention to the discovery, which was accordingly for the first time brought into general notice. It will be seen that there are not many facts of general interest relating to the actual discovery beyond the courage with which the work was commenced in a totally unpromising direction, and the scant attention it received after being made for us. We may admit that interest centres chiefly in the tremendous consequences which flowed from it. We now recognise that many other phenomena are bound up with this waxing and waning of the solar spots.Other phenomena sympathetic We might be prepared for a sympathy in phenomena obviously connected with the sun itself; but it was an unexpected and startling discovery that magnetic phenomena on the earth had also a sympathetic relation with the changes in sun-spots, and it is perhaps not surprising that when once this connection of solar and terrestrial phenomena was realised, various attempts have been made to extend it into regions where we cannot as yet allow that it has earned a legitimate right of entry. We have heard of the weather and of Indian famines occurring in cycles identical with the sun-spot cycle; and it is obvious how tremendously important it would be for us if this were found to be actually the case. For we might in this way predict years of possible famine and guard against them; or if we could even partially foretell the kind of weather likely to occur some years hence, we might take agricultural measures accordingly. The importance of the connection, if only it could be established, is no doubt the reason which has misled investigators into laying undue stress on evidence which will not bear close scrutiny.and others not. For the present we must say decidedly that no case has been made out for paying serious attention to the influence of sun-spots on weather. Nevertheless, putting all this aside, there is quite enough of first-rate importance in the sequel to Schwabe’s discovery.
Let us review the facts in order. Most of us, though we may not have had the advantage of seeing an actual sun-spot through a telescope, have seen drawings or photographs of spots. There is a famous drawing made by James Nasmyth (of steam-hammer fame), in July, 1864, which is of particular interest, because at that time Nasmyth was convinced—and he convinced many others with him—that the solar surface was made up of a miscellaneous heap of solid bodies in shape like willow leaves, or grains of rice, thrown together almost at random, and the drawing was made by him to illustrate this idea. Comparing a modern photograph with it, we see that there is something to be said for Nasmyth’s view, which attracted much attention at the time and occasioned a somewhat heated controversy. But since the invention of the spectroscope it has become quite obsolete; it probably does not correspond in any way to the real facts.Greenwich sun records. But instead of looking at pictures which have been enlarged to show the detailed structure in and near a spot, we will look at a series of pictures of the whole sun taken on successive days at Greenwich in which the spots are necessarily much smaller, but which show the behaviour of the spots from day to day. (See Plates [X.] and [XI.]) From the date at the foot of each it will be seen that they gradually cross the disc of the sun (a fact first discovered by Galileo in 1610),The sun’s rotation. showing that the sun rotates on an axis once in about every twenty-five days. There are many interesting facts connected with this rotation; especially that the sun does not rotate as a solid body, the parts near the (Sun’s) Equator flowing quicker than those nearer the Poles; but for the present we cannot stop to dwell upon them. What interests us particularly is the history, not from day to day, but from year to year, as Schwabe has already given it for a series of years.