Astronomical Discovery

contrary to

earch, and others accidentally in the course of work directed to a totally different end; but so far we have n

as first made in 1843, though he had himself been convinced some years earlier. In 1857 the Royal Astronomical Society awarded him their gold medal for the discovery; and in the address delivered on the occasion the President commenced by drawing attention to this very fact,Nothing expected from

, more thoroughly than his predecessors had done, the laws of a remarkable phenomenon, which it had long been the fashion to neglect. He could hardly have anticipated the kind of result at which he has arrived; at the same time we cannot imagine a course of proceeding better calculated for its detection, e

t aut evanescunt,' says Keill in 1739.-

oint de règle certaine de leur formation, ni de leur nombre et de l

loi dans leur apparitions,' says Le M

nitude, number, or in the time of their appearance or c

'ont rien de regulier,' says Lalande in

lume of his 'Astronomy' (p. 20), published in 1814, where treating of the solar s

trary to expectation. It is a lesson to us that not even the most unlikely line of work is to be despised; for the outcome of Schwabe's work was the first step in the whole series of discoveries whi

's anno

s for further material, in 1843 he ventured to make his definite announcement as follows:-"From my earlier observations, which I have communicated annually to this journal, there was manifest already a certain periodicity of sun-spots; and the probability of this being really the case is confirmed by this year's results. Although I gave in volume 15 the total numbers of groups for the years 1826-1837, nevertheless I will repeat here a complete series of all my observations of sun-spots, giving not only the number of groups, but also the number of days of observation, an

Numb

s. Da

pots.

rvat

118 2

161

225

199

190

149

84

33 13

51 12

173 1

272

33

282

162

152

102 1

68

34 14

(52) (1

about five years they are so numerous that during this period few days, if any, are free from spots. The sequel must show whether this period is constant,

18,

19,

ken at the Royal Observatory

little a

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 indicate

ed 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 fami

ee 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.)

20,

21,

aken at the Royal Observator

s num

cope, and the results when submitted to certain necessary calculations are published year by year. It is clearly a more accurate estimate of the spottedness of the sun to take the total area of all the spots rather than their mere number, for in the latter case a large spot and a small one count equally. Hence the Greenwich records will perhaps give us an even better idea of the periodicity than Wolf's numbers. Now, at the same observatory magnetic observations are also made continuously. If a magnet be suspended freely we are accustomed to say that it will point to the North Pole; but this is only very roughly true. In the first place, it is probably well known to you that there is a considerable deviation from due north owing to the fact that the magnetic North Pole is not the same as the geographical North Pole; but this for the present need not concern us.Magnetic fluctuations. What does concern us is, that if the needle is hung up and left long enough to come to rest, it does not then remain steadily at rest, but executes slow and small oscil

te

little stronger or a little weaker than before, and these variations are not represented by any actual movement of the needle, though they can be measured by proper experiments. We can, however, imagine them represented by a movement of the end of the needle if we suppose it made of elastic material,Daily curves. so that it would lengthen when the force was greater and contract slightly when the force was less. If a pencil were attached to the end of such an elastic needle so as to make a mark on a

from month to month in any particular year, and the law of change is such that in years when there are many sun-spots we get a large open curve similar to those found in the summer, while for years when there are few sun-spots we get small close curves very like those in the winter. Hence we have two definite conclusions suggested: firstly, that the changes of force are sympathetic with the changes in the sun-spots; and secondly, that times of maximum sun-spots correspond to summer, and times of minimum to winter. And here I must admit that th

te

te

such occasions it is often necessary to replace it by hand. Then again, the vane may turn in the opposite direction, sending the pencil inconveniently to the other side of the record. During the year it is easy to count the number of complete changes of wind in either direction, and subtracting one number from the other, we get the excess of complete revolutions of the vane in one direction over that in the other. Now if these rather arbitrary numbers are set down year by year, or plotted in the shape of a diagram, we get a curve which may be compared with the sun-spot curve, and during a period of no less than sixteen years-from 1858 to 1874-there was a remarkable similarity between the two diagrams. From this evidence alone it might fairly be inferred that the sun-spots had some curious effect upon the weather at Greenwich, traceable in this extraordinary way in the changes of the wind. But the particular way in which these changes are recorded is so arbitrary that we should naturally feel surprise if there was a real connection between the two phenomena; and fortunately

follo

ge of the sun's disc; but even with this limitation it can easily be established that the facul? vary in number and size from year to year much in the same way as the spots, and this conclusion is amply confirmed by the beautiful method of observing the facul? with the new instrument designed by Professor Hale of the Yerkes Observatory. With this instrument, called a spectroheliograph, it is possible to photograph the facul? in all parts of the sun's disc, and thus to obtain a much more complete history of them, and there is no doubt whatever of the

year by the Osler Anemometer Vane of the Royal Observatory, Greenwich (the

er I

the Vane Curve. The break in 1882 in the Vane Curve is due

te

ph; and Professor Hale has succeeded in photographing spots, facul?, and prominences all on the same plate. But although many have made the attempt (and Professor Hale, perhaps, a more

ses o

iles in length possibly, but still not more than 200 miles wide;Total eclipses rare. and in order to see the sun totally eclipsed even on the rare occasions when it is possible at all (for, as already remarked, in the majority of cases the eclipse is only partial), we must occupy some station in this narrow belt or track, which often tantalisingly passes over either the ocean or some regions not easily accessible to civilised man. Moreover, if we travel to such favoured spots the whole time during which the sun is totally eclipsed cannot exceed a few minutes, and hence observations are made under rather hurried and trying conditions. In these modern days of photography it is easier to take advantage of these precious moments than it used to be when there was only the eye and memory of an excited observer to rely upon. It is perhaps not surprising t

ance for our immediate purpose, it has gradually been established by comparing the photographs of one eclipse with those of another,Corona follows spots. that the corona itself undergoes distinct changes in form in the same period which governs the changes of sun-spots. When there are many sun-spots the corona spreads out in all directions from the edge of the sun's disc; when there are few sun-s

in sun-spots seem to influence changes in our magnets on the earth; but one of the theories put forward in explanation, and one by no means the least plausible, is that this influence may come, not from the sun-spots themselves, but from some other solar phenomenon which varies in sympathy with them; and in particular that it may come from the corona.Corona may influence magnets. These wings which reach out at sun-spot minimum can be seen to extend a considerable distance, and there is no reason to suppose that they actually cease at the point where t

mportance

ntion to proper conditions results of overwhelming practical importance have been obtained from these forces, which might have been, and for many centuries were, neglected as too trivial to be worth attention. Recently the world has been startled by the discovery of new elements, such as radium, whose very existence was only detected by a triumph of scientific acuteness in investigation, and yet which promise to yield influences on our lives which may overwhelm in import

ots which he had been assured were of no interest and exhibited no laws, and were generally unprofitable-that he was taking the first step in the invention of the great science of Solar Physics!