During the last five or six years a section of the scientific world has been exercised with the question how far the condition of the sun’s surface with regard to spots affects our earth’s condition as to weather, and therefore as to those circumstances which are more or less dependent on weather. Unfortunately, the question thus raised has not presented itself alone, but in company with another not so strictly scientific, in fact, regarded by most men of science as closely related to personal considerations—the question, namely, whether certain indicated persons should or should not be commissioned to undertake the inquiry into the scientific problem. But the scientific question itself ought not to be less interesting to us because it has been associated, correctly or not, with the wants and wishes of those who advocate the endowment of science. I propose here to consider the subject in its scientific aspect only, and apart from any bias suggested by the appeals which have been addressed to the administrators of the public funds. It is hardly necessary to point out, in the first place, that all the phenomena of weather are directly referable to the sun as their governing cause. His rays poured upon our air cause the more important atmospheric currents directly. Indirectly they cause modifications of these currents, because where they fall on water or on moist surfaces they raise aqueous vapour into the air, which, when it returns to the liquid form as cloud, gives up to the surrounding air the heat which had originally vaporized the water. In these So also every drop of rain or snow, every particle of liquid or of frozen water in mist or in cloud, owes its birth to the sun. The questions addressed of old to Job, “Hath the rain a father? or who hath begotten the drops of dew? out of whose womb came the ice? and the hoary frost of heaven, who hath gendered it?” have been answered by modern science, and to every question the answer is, The Sun. He is parent of the snow and hail, as he is of the moist warm rains of summer, of the ice which crowns the everlasting hills, and of the mist which rises from the valleys beneath his morning rays. Since, then, the snow that clothes the earth in winter as with a garment, and the clouds that in due season drop fatness on the earth, are alike gendered by the sun; since every movement in our air, from the health-bringing breeze to the most destructive hurricane, owns him as its parent; we must at the outset admit, that if there is any body I suppose there must have been a time when men were not altogether certain whether the varying apparent path of When this discovery was effected, men made the most important and, I think, the most satisfactory step towards the determination of cyclic associations between solar and terrestrial phenomena. It is for that reason that I refer specially to the point. In reality, it does not appertain to my subject, for seasons and sun-spots are not associated. But it admirably The evidence thus afforded is by no means promising, then, so far as the prediction of special storms, or floods, or droughts is concerned. It would seem that if past experience can afford any evidence in such matters, men may expect to recognize cycles of weather change long before they recognize corresponding solar cycles (presuming always that such cycles exist), and that they may expect to find the recognition of such association utterly barren, so far as the possibility of predicting definite weather changes is concerned. It would seem that there is no likelihood of anything better than what Sir J. Herschel said might be hoped for hereafter. “A lucky hit may be made; nay, some rude approach to the perception of a ‘cycle of seasons’ may possibly be obtainable. But no person in his senses would alter his plans of conduct for six months in advance in the most trifling particular on the faith of any special prediction of a warm or a cold, a wet or a dry, a calm or a stormy, summer or winter”—far less of a great storm or flood announced for any special day. But let us see what the cycle association between solar spots and terrestrial weather actually is, or rather of what nature it promises to be, for as yet the true nature of the association has not been made out. It has been found that in a period of about eleven years the sun’s surface is affected by what may be described as a wave of sun-spots. There is a short time—a year or so—during which scarce any spots are seen; they become more and more numerous during the next four or five years, until they attain a maximum of frequency and size; after this they wane in number and dimensions, until at length, about eleven years from the time when he had before been freest from Now there are some terrestrial phenomena which we might expect to respond in greater or less degree to the sun’s changes of condition with respect to spots. We cannot doubt that the emission both of light and of heat is affected by the presence of spots. It is not altogether clear in what way the emission is affected. We cannot at once assume that because the spots are dark the quantity of sunlight must be less when the spots are numerous; for it may well be that the rest of the sun’s surface may at such times be notably brighter than usual, and the total emission of light may be greater on the whole instead of less. Similarly of the emission of heat. It is certain that when there are many spots the surface of the sun is far less uniform in brightness than at other times. The increase of brightness all round the spots is obvious to the eye when the sun’s image, duly enlarged, is received upon a screen in a darkened room. Whether the total emission of light is increased or diminished has not yet been put to the test. Professor Langley, of the Alleghany Observatory, near Pittsburg, U.S., has carefully measured the diminution of the sun’s emission of light and heat on the assumption that the portion of the surface not marked by spots remains unchanged in lustre. But until More satisfactory would seem to be the measurements which have been made by Professor Piazzi Smyth, at Edinburgh, and later by the Astronomer Royal at Greenwich, into the underground temperature of the earth. By examining the temperature deep down below the surface, all local and temporary causes of change are eliminated, and causes external to the earth can alone be regarded as effective in producing systematic changes. “The effect is very slight,” I wrote a few years ago, “indeed barely recognizable. I have before me as I write Professor Smyth’s sheet of the quarterly temperatures from 1837 to 1869 at depths of 3, 6, 12, and 24 French feet. Of course the most remarkable feature, even at the depth of 24 feet, is the alternate rise and fall with the seasons. But it is seen that, while the range of rise and fall remains very nearly constant, the crests and troughs of the waves lie at varying levels.” After describing in the essay above referred to, which appears in my “Science Byways,” the actual configuration of the curves of temperature both for seasons and for years, and the chart in which the sun-spot waves and the temperature waves are brought into comparison, I was obliged to admit that the alleged association between the sun-spot period and the changes of underground temperature did not seem to me very clearly made out. It appears, however, there is a slight increase of temperature at the time when the sun-spots are least numerous. That the earth’s magnetism is affected by the sun’s condition with respect to spots, seems to have been more clearly made out, though it must be noted that the Astronomer Royal considers the Greenwich magnetic observations inconsistent with this theory. It seems to have been rendered at least extremely probable that the daily oscillation of the magnetic needle is greater when spots are numerous than when there are few spots or none. Magnetic Thus far, however, we have merely considered relations which we might fairly expect to find affected by the sun’s condition as to spots. A slight change in his total brightness and in the total amount of heat emitted by him may naturally be looked for under circumstances which visibly affect the emission of light, and presumably affect the emission of heat also, from portions of his surface. Nor can we wonder if terrestrial magnetism, which is directly dependent on the sun’s emission of heat, should be affected by the existence of spots upon his surface. It is otherwise with the effects which have recently been associated with the sun’s condition. It may or may not prove actually to be the case that wind and rain vary in quantity as the sun-spots vary in number (at least when we take in both cases the average for a year, or for two or three years), but it cannot be said that any such relation was antecedently to be expected. When we consider what the sun actually does for our earth, it seems unlikely that special effects such as these should depend on relatively minute peculiarities of the sun’s surface. There is our earth, with her oceans and continents, turning around swiftly on her axis, and exposed to his rays as a whole. Or, inverting the way of viewing matters, there is the sun riding high in the heavens of any region of the earth, pouring down his rays upon that region. We can understand how in the one case that rotating orb of the earth may receive rather more or rather less heat from the sun when he is spotted than when he is not, or how in the other way of viewing matters, that But of course all such considerations as to antecedent probabilities must give way before the actual evidence of observed facts. Utterly inconsistent with all that is yet known of the sun’s physical action, as it may seem, on À priori grounds, to suppose that spots, currents, or other local disturbances of the sun’s surface could produce any but general effects on the earth as a whole, yet if we shall find that particular effects are produced in special regions of the earth’s surface in cycles unmistakably synchronizing with the solar-spot-cycle, we must accept the fact, whether we can explain it or not. Only let it be remembered at the outset that the earth is a large place, and the variations of wind and calm, rain and drought, are many and various in different regions. Whatever place we select for examining the rainfall, for example, we are likely to find, in running over the records of the last thirty years or so, some seemingly oscillatory changes; in the records of the winds, again, we are likely to find other seemingly oscillatory changes; if none of these records provide anything which seems in any way to correspond I mention this matter at the outset, because many who are anxious to find some such cycle of seasons as Sir John I would not have it understood, however, that I consider all the cycles now to be referred to as unreal, or even that the supposed connection between them and the solar cycle has no existence. I only note that there are thousands, if not tens of thousands, of relations among which cycles may be looked for, and that there are perhaps twenty or thirty cases in which some sort of cyclic association between certain meteorological relations and the period of the solar spots presents itself. According to the recognized laws of probability, some at least amongst these cases must be regarded as accidental. Some, however, may still remain which are not accidental. Among the earliest published instances may be mentioned Mr. Baxendell’s recognition of the fact that during a certain series of years, about thirty, I think, the amount of rainfall at Oxford was greater under west and south-west winds than under south and south-east winds when sun-spots were most numerous, whereas the reverse held in years when there were no spots or few. Examining the meteorological records of The Rev. Mr. Main, Director of the Radcliffe Observatory at Oxford, found that westerly winds were slightly more common (as compared with other winds) when sun-spots were numerous than when they were few. Mr. Meldrum, of Mauritius, has made a series of statistical inquiries into the records of cyclones which have traversed the Indian Ocean between the equator and 34 degrees south latitude, in each year from 1856 to 1877, noting the total distances traversed by each, the sums of their radii and areas, their duration in days, the sums of their total areas, and their relative areas. His researches, be it marked in passing, are of extreme interest and value, whether the suggested connection between sun-spots and cyclones (in the region specified) be eventually found to be a real one or not. The following are his results, as described in Nature by a writer who manifestly favours very strongly the doctrine that an intimate association exists between solar maculation (or spottiness) and terrestrial meteorological phenomena:— “The period embraces two complete, or all but complete, sun-spot periods, the former beginning with 1856 and ending in 1867, and the latter extending from 1867 to about the present time [1877]. The broad result is that the number of cyclones, the length and duration of their courses, and the extent of the earth’s surface covered by them all, reach the maximum in each sun-spot period during the years of maximum maculation, and fall to the minimum during the years of minimum maculation. The peculiar value of these results lies in the fact that the portion of the earth’s surface over which this investigation extends, is, from its geographical position and what may be termed its meteorological homogeneity, singularly well fitted to bring out prominently any connection that may exist between the condition of the sun’s surface and atmospheric phenomena.” The writer proceeds to describe an instance in which It was natural that the great Indian famine, occurring at a time when sun-spots were nearly at a minimum, should by some be directly associated with a deficiency of sun-spots. In this country, indeed, we have had little reason, during the last two or three years of few sun-spots, to consider that drought is one of the special consequences to be attributed to deficient solar maculation. But in India it may be different, or at least it may be different in Madras, for it has been satisfactorily proved that in some parts of India the The hope that famines may be abated, or, at least, some of their most grievous consequences forestalled by means of solar observatories, does not appear very clearly made out. Rather it would seem that the proper thing to do is to investigate the meteorological records of different Indian regions, and consider the resulting evidence of cyclic changes without any special reference to sun-spots; for if sun-spots may cause drought in one place, heavy rainfall in another, winds here and calms there, it seems conceivable that the effects of sun-spots may differ at different times, as they manifestly do in different places. Let us turn, however, from famines to shipwrecks. Perhaps, if we admit that cyclones are more numerous, and blow more fiercely, and range more widely, even though it be over one large oceanic region only, in the sun-spot seasons than at other times, we may be assured, without further research, that shipwrecks will, on the whole, be more numerous near the time of sun-spot maxima than near the time of sun-spot minima. The idea that this may be so was vaguely shadowed forth in a poem of many stanzas, called “The Meteorology of the Future: a Vision,” which appeared in Nature for July 5, 1877. I do not profess to understand precisely what the object of this poem may have been—I mean, whether it is intended to support or not the theory that sun-spots influence the weather. Several stanzas are very “In fame to none will yield, He led the band who reaped renown On India’s famine field. “Was he the man to see thee die? Thou wilt not tax him—come? The dead man groaned—‘I met my death Through a sun-spot maximum.’” The first definite enunciation, however, of a relation between sun-spots and shipwrecks appeared in September, 1876. Mr. Henry Jeula, in the Times for September 19, stated that Dr. Hunter’s researches into the Madras rainfall had led him to throw together the scanty materials available relating to losses posted on Lloyd’s loss book, to ascertain if any coincidences existed between the varying number of such losses and Dr. Hunter’s results. “For,” he proceeds, “since the cycle of rainfall at Madras coincides, I am informed, with the periodicity of the cyclones in the adjoining Bay of Bengal” (a relation which is more than doubtful) “as worked out by the Government Astronomer at Mauritius” (whose researches, however, as we have seen, related to a region remote from the Bay of Bengal), “some coincidence between maritime casualties, rainfalls, and sun-spots appeared at least possible.” In passing, I may note that if any such relation were established, it would be only an extension of the significance of the cycle of cyclones, and could have no independent value. It would certainly follow, if the cycle of cyclones is made out, that shipwrecks being more numerous, merchants would suffer, and we should To return, however, to the sun’s influence upon shipwrecks. Mr. Jeula was “only able to obtain data for two complete cycles of eleven years, namely, from 1855 to 1876 inclusive, while the period investigated by Dr. Hunter extended from 1813 to 1876, and his observations related to Madras and its neighbourhood only, while the losses posted at Lloyd’s occurred to vessels of various countries, and happened in different parts of the world. It was necessary to bring these losses to some common basis of comparison, and the only available one was the number of ‘British registered vessels of the United Kingdom and Channel Islands’—manifestly an arbitrary one. I consequently cast The results may be thus presented:— Taking the four years of each cycle when sun-spots were least in number, Mr. Jeula found the mean percentage of losses in registered vessels of the United Kingdom and Channel Islands to be 11·13, and the mean percentage of losses in the total posted in the entire cycle of eleven years to be 8·64. In the four years when sun-spots were intermediate in number, that is in two years following the minimum and in two years preceding the minimum, the respective percentages were 11·91 and 9·21. Lastly, in the three years when sun-spots were most numerous, these percentages were, respectively, 12·49 and 9·53. That the reader may more clearly understand what is meant here by percentages, I explain that while the numbers 11·13, 11·91 and 12·49 simply indicate the average number of wrecks (per hundred of all the ships registered) which occurred in the several years of the eleven-years cycle, the other numbers, 8·64, 19·21, and 9·53, indicate the average number of wrecks (per hundred of wrecks recorded) during eleven successive years, which occurred in the several years of the cycle. The latter numbers seem more directly to the purpose; and as the two sets agree pretty closely, we may limit our attention to them. Now I would in the first place point out that it would have been well if the actual number or percentage had been indicated for each year of the cycle, instead of for periods of four years, four years, and three years. Two eleven-year cycles give in any case but meagre evidence, and it would have been well if the evidence had been given as fully as The total rainfall at Port Louis, between the years 1855 and 1868 inclusive, is as follows:—
I think no one, looking at these numbers as they stand, can recognize any evidence of a cyclic tendency. If we represent the rainfall by ordinates we get the accompanying
Nothing could be more satisfactory, but nothing, I venture to assert, more thoroughly inconsistent with the true method of statistical research. When we consider that the loss of ships depends, not only on a cause so irregularly variable (to all seeming) as wind-storms, but also on other matters liable to constant change, as the variations in the state of trade, the occurrence of wars and rumours of wars, special events, such as international exhibitions, and so forth, we perceive that an even wider range of survey is required to remove the effects of accidental peculiarities in their case, than in the case of rainfall, cyclones, or the like. I cannot but think, for instance, that the total number of ships lost in divers ways during the American war, and especially in its earlier years (corresponding with two of the three maximum years of sun-spots) may have been greater, not merely absolutely but relatively, than in other years. I think it conceivable, again, that during the depression following the great commercial panic of 1866 (occurring at a time of minimum solar maculation, as already noticed) the loss of ships may have been to some degree reduced, relatively as well as absolutely. We know that when trade is unusually active many ships have sailed, and perhaps may still be allowed to sail (despite Mr. Plimsoll’s endeavours), which should have been broken up; whereas in times of trade depression the ships actually afloat are likely to be, on the average, of a better class. So also, when, for some special reason, passenger traffic at sea is abnormally increased. I merely mention these as illustrative cases of causes not (probably) dependent on sun-spots, which may (not improbably) have affected the results examined by Mr. Jeula. I think it possible that those results, if presented for each year, would have indicated the operation of such causes, naturally masked when sets of four years, four years, and three years are taken instead of single years. I imagine that considerations such as these will have to be taken into account and disposed of before it will be unhesitatingly admitted that sun-spots have any great effect in increasing the number of shipwrecks. If these hopes are really justified by the facts of the case, it would be well that the matter should be as quickly as possible put to the test. No one would be so heartless, I think, as to reject, through an excess of scientific caution, a scheme which might issue in the saving of many lives from famine or from shipwreck. And on the other hand, no one, I think, would believe so ill of his fellow-men as to suppose for one moment that advantage could be taken of the sympathies which have been aroused by the Indian famine, or which may from time to time be excited by the record of great disasters by sea and land, to advocate bottomless schemes merely for purposes of personal advancement. We must now, perforce, believe that those who advocate the erection of new observatories and laboratories for studying the physics of the sun, have the most thorough faith in the scheme which they proffer to save our Indian population from famine and our seamen from shipwreck. But they, on the other hand, should now also believe that those who have described the scheme as entirely hopeless, do really so regard it. If we exonerate them from the charge of responding to an appeal for food by offering spectroscopes, they in turn should exonerate us from the charge of denying spectroscopes to the starving millions of India though knowing well that the spectroscopic track leads straight to safety. I must acknowledge I cannot for my own part see even that small modicum of hope in the course suggested which would suffice to justify its being followed. In my opinion, one ounce of rice would be worth more (simply because it would be worth something) than ten thousand tons of spectroscopes. Of what use can it be to know, for instance, that the three years of least solar maculation will probably give a rainfall less than that for the preceding or following three years, if the middle year of the three, when the spots are most numerous of all, may haply show plenteous rainfall? Or it may be the first of the three, or the last, which is thus well supplied, while a defect in the other two, or in one of the others, brings the total triennial rainfall below the average. What provision could possibly be made under such circumstances to meet a contingency which may occur in any one of three years? or, at least, what provision could be made which would prove nearly so effective as an arrangement which could readily be made for keeping sufficient Government stores at suitable stations (that is, never allowing such stores to fall at the critical season in each year below a certain minimum), and sending early telegraphic information of unfavourable weather? Does any one suppose that the solar rice-grains are better worth watching for such a purpose than the terrestrial rice-grains, or that it is not well within the resources of modern science and modern means of communication and transport, to make sufficient preparation each year for a calamity always possible in India? And be it noticed that if, on the one hand, believers in solar safety from famine may urge that, in thus objecting to their scheme, I am opposing what might, in some year of great famine and small sun-spots, save the lives of a greater number than would be saved by any system of terrestrial watchfulness, I would point out, on the other, that the solar scheme, if it means anything at all, Supposing even it were not only proved that sun-spots exert such and such effects, but that this knowledge can avail to help us to measures of special precaution, how is the study of the sun going to advance our knowledge? In passing, let it be remarked that already an enormous number of workers are engaged in studying the sun in every part of the world. The sun is watched on every fine day, in every quarter of the earth, with the telescope, analyzed with the spectroscope, his prominences counted and measured, his surface photographed, and so forth. What more ought to be or could be done? But that is not the main point. If more could be done, what could be added to our knowledge which would avail in the way of prediction? “At present,” says Mr. Balfour Stewart, “the problem has not been pursued on a sufficiently large scale or in a sufficient number of places. If the attack is to be continued, the skirmishers should give way to heavy guns, and these should be brought to bear without delay now that the point of attack is known.” In other words, now that we know, according to the advocates of these views, that meteorological phenomena follow roughly the great solar-spot period, we should prosecute the attack in this direction, in order to find out—what? Minor periods, perhaps, with which meteorological phenomena may still more roughly synchronize. Other such periods are already known with which meteorological phenomena have never yet been associated. New details of the sun’s surface? No one has yet pretended that any of the details already known, except the spots, affect terrestrial weather, and the idea that peculiarities so minute as hitherto to have escaped detection can do so, is as absurd, on the face of it, as the supposition that minute details in the structure of a burning Lastly, I would urge this general argument against a theory which seems to me to have even less to recommend it to acceptance than the faith in astrology.8 If it requires, |