comparison between the quantity of heat received by the whole earth on a day in June and on a day in December. Either way of viewing the matter is instructive; and I believe many of my readers will be surprised when they hear what is the actual amount of difference.

We receive in fact, on June 30th, less heat and light than dwellers at our antipodes receive on December 30th, by the amount which would be lost if an opaque disc having a diameter equal to one-fourth of the sun's,* came upon the sun's face as seen on December 30 at our antipodes. It need hardly be said that no spots whose effects would be comparable with those produced by such a disc of blackness have ever been seen upon the face of the sun. Spots are not black or nearly black, even in their very nucleus. The largest ever seen has not had an extent approaching that of our imagined black disc, even when the whole dimensions of the spot, -nucleus, umbra, and penumbra,-have been taken into account. Moreover, all round a spot there is always a region of increased brightness, making up to a great degree, if not altogether, for the darkness of the spot itself. So that unquestionably the summer heat in the southern hemisphere exceeds the summer heat in our hemisphere to a much more marked degree than the heat given out by the sun when he is without spots exceeds the heat of a spotted sun.

It is, however, rather difficult to ascertain what effect is to be ascribed to this peculiarity. It is certain that the Australian summer differs in several important respects from the European summer; but it is not easy to say how much of the difference is due to the peculiarity we have been considering, and how much to the characteristic distinction between the northern and southern halves of the earth,the great excess of water surface over land surface in the southern hemisphere.

*It is easily shown that such would be the size of the imagined black disc. For the sun's distance varies from about 93 millions of miles to about 90 millions, or in the proportion of 31 to 30.

Hence the size of his disc varies in the proportion of 31 times 31 to 30 times 30, or as 961 to 900. The defect of the latter number 900 amounts to 61, which is about a sixteenth part of the larger number. But a black disc having a diameter equal to a quarter of the sun's would cut off precisely a sixteenth part of his light and heat, which was the fact to be proved.

It is worthy of notice, however, that even in this case, where we cannot doubt that a great difference must exist in the solar action at particular seasons, we find ourselves quite unable to recognise any peculiarities of weather as certainly due to this difference.

I have spoken of a second way of viewing the difference in question, by considering it as it affects the whole earth. The result is sufficiently surprising. It has been shown by the researches of Sir J. Herschel and Pouillet, that on the average our earth receives each day a supply of heat competent to heat an ocean 260 yards deep over the whole surface of the earth from the temperature of melting ice to the boiling point. Now, on or about June 30, the supply is one thirtieth greater, while on or about December 30, the supply is one thirtieth less. Accordingly, on June 30, the heat received in a single day would be competent only to raise an ocean 251 yards deep from the freezing to the boiling point, whereas on December 30 the heat received from the sun would so heat an ocean 2683 yards deep. The mere excess of heat, therefore, on December 30, as compared with June 30, would suffice to raise an ocean more than 17 yards deep and covering the whole earth, from the freezing point to the temperature of boiling water! It will not be regarded as surprising if terrestrial effects of some importance should follow from so noteworthy an excess, not merely of light and heat, but of gravitating force, of magnetic influence, and of actinic or chemical action, exerted upon the earth as a whole. Accordingly we find that there is a recognisable increase in the activity of the earth's magnetism in December and January as compared with June and July. assuredly the effect produced is not of such a character as to suggest that we should find the means of predicting weather if it were posssible for us now to discover any solar law of change resulting in a corresponding variation of solar action upon the earth.

But

This leads us to consider the first great law of solar change as distinguished from systematic variations like the sun's varying change of distance and his varying daily path on the heavens. This law is that which regulates the increase and decrease of the solar spots within a period of about eleven years. The sun's condition does

not, indeed, admit of being certainly predicted by this law, since it not unfrequently happens that the sun shows few spots for several weeks together, in the very height of the time of spot-frequency, while on the other hamd it often happens that many and large spots are seen at other times. Nevertheless, this general law holds, that, on the whole, and taking one month with another, there is a variation in spot-frequency, having for its period an interval of rather more than eleven years. Now, the difference between a year of maximum spot-frequency, and one of minimum frequency, is very noteworthy, notwithstanding the exceptional features just mentioned, which show themselves but for short periods. This will be manifest on the consideration of a few typical instances. Thus, in the year 1837, the sun was observed on 168 days, during which he was not once seen without spots, while no less than 333 new groups made their appearance. This was a year of maximum spot-frequency. In 1843, the sun was observed on 312 days, and on no less than 149 of these no spots could be seen, while only 34 new groups made their appearance. This was a year of minimum spot-frequency. Passing to the next maximum year, we find that in 1848 the sun was observed on 278 days, during which he was never seen without spots, while 330 new spots made their appearance. In 1855 and 1856 together, he was observed on 634 days, on 239 of which he was without spots, while only 62 new groups made their appearance. The next maximum was not so marked as usual, that is, there was not so definite a summit, if one may so speak, to the wave of increase; but the excess of spot-frequency was none the less decided. Thus, in the four years, 1858, '59, '60, '61, the sun was observed on 335, 343, 333, and 322 days, on not one of which he was spotless, while the numbers of new groups for these four years were respectively, 202, 205, 211, and 204. The minimum in 1867 was very marked, as 195 days out of 312 were without spots, and only 25 new groups appeared. The increase after 1867 was unusually rapid, since in 1869 there were no spotless days, and 224 new groups were seen, though the sun was only observed on 196 days. The number of spots in 1870, 1871, and 1872, as well as their magnitude and duration, have been above what

is usual, even at the period of maximum spot-frequency.

From all this it will be manifest that we have a well-marked peculiarity to deal with, though not one of perfect uniformity. Next to the systematic changes already considered, this alternate waxing and waning of spot-frequency might be expected to be efficient in producing recognisable weather changes. Assuredly, if this should not appear to be the case, we should have to dismiss all idea that the sun-spots are weather-rulers.

Now, from the first discovery of spots, it was recognised that they must, in all probability, affect our weather to some degree. It was noticed, indeed, that our auroras seemed to be in some way influenced by the condition of the sun's surface, since they were observed to be more numerous when there are many spots than when there are few or none. Singularly enough, the effect of the spots on temperature was not only inquired into much later (for we owe to Cassini and Mairan the observation relating to auroras), but was expected to be of an opposite character from that which is in reality produced. Sir W. Herchel formed the opinion that when there are most spots the sun gives out most heat, notwithstanding the diminution of light where the spots are. He sought for evidence on this point in the price of corn in England, and it actually appeared, though by a mere coincidence, that corn had been cheapest in years of spot-frequency, a result regarded by Herschel as implying that the weather had been warmer on the whole in those years. It was well pointed out, however, by Arago, that "in these matters we must be careful how we generalise facts before we have a very considerable number of observations at our disposal." The peculiarities of weather in a single and not extensive country like England, are quite insufficient to supply an answer to the wide question dealt with by Herschel. The weather statistics of many countries must be considered and compared. Moreover, very long periods of time must be dealt with.*

* When Herschel made his researches into this subject, the law of spot-frequency had not been discovered. He would probably have found tion of the seven years of plenty and the seven in this law, as some have since done, the explanayears of famine typified by the fat kine and lean

M. Gautier, of Geneva, and later MM. Arago and Barratt made a series of researches into the tabulated temperature at several stations, and for many successive years. They arrived at the conclusion that, on the whole, the weather is coolest in years of spot-frequency.

But recently the matter has been more closely scrutinised, and it has been found that the effects due to the great solar spot period, although recognisable, are by no means so obvious as had been anticipated. These effects may be divided into three classes, those affecting (1) temperature, (2) rainfall, and (3) terrestrial magnetism.

As respects the first, it has been discovered that when underground temperatures are examined, so that local and temporary causes of change are eliminated, there is a recognisable diminution of temperature in years when spots are most frequent. We owe this discovery to Professor C. P. Smyth, Astronomer Royal for Scotland. The effect is very slight; indeed, barely recognisable. I have before me, as I write, Professor Smyth's chart 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 long and careful scrutiny, I find myself compelled to admit that I cannot find the slightest evidence in this chart of a connection between underground temperatures and the eleven years period of sun spots. I turn, therefore, to the chart in which the annual means are given; and noting in the means at the

lesser depths "confusion worse confounded" (this, of course, is no fault of Professor Smyth's, who here merely records what had actually taken place), I take the temperatures at a depth of 24 French feet. Now, neglecting minor features, I find the waves of temperature thus arranged. They go down to a little more than 46 degrees of the common thermometer in 1839-40; rise to about 47 degrees in 1847; sink to 474 degrees in 1849; mount nearly to 47 degrees again in 1852-53; are at 47 degrees in 1856-57; are nearly at 48 degrees in 1858-59; then they touch 47 degrees three times (with short periods of rising between), in 1860, 1864, and 1867; and rise above 47 degrees in 1869. Now if we remember that there were maxima of spots in 1837, 1848, 1859-60, and 1870, while there were minima in 1843, and 1855-56, I think it will be found to require a somewhat lively imagination to recognise a very striking association between the underground temperature and the sun's condition with respect to spots. If many spots imply diminution of heat, how does it come that the temperature rises to a maximum in 1859, and again in 1869? if the reverse, how is it that there is a minimum in 1860 ? I turn, lastly, to the chart in which the sun-spot waves and the temperature waves are brought into actual comparison, and I find myself utterly unable to recognise the slightest association between them. Nevertheless, I would not urge this with the desire of in any way throwing doubt upon the opinion to which Professor Smyth has been led, knowing well that the long and careful examination he has given to this subject in all its details, may have afforded ample though not obvious evidence for the conclusions at which he has arrived. I note also, that, as he points out, Mr. Stone, director of the Cape Town Observatory, and Mr. Cleveland Abbe, director of the Cincinnati Observatory, have since, "but it is believed quite independently, published similar deductions touching the earth's temperature in reference to sun-spots." All I would remark is, that the effect is very slight and very far from being obvious at a first inspection. Next as to rainfall and wind.

Here, again, we have results which can hardly be regarded as striking, except in the forcible evidence they convey of the insignificance of the effects which are to

be imputed to the great eleven-year spot period. We owe to Mr. Baxendell, of Manchester, the most complete series of investigations into this subject. He finds that at Oxford, during the years when sun-spots were most numerous, the amount of rainfall under west and south-west winds was greater than the amount under south and south-east winds; while the reverse was the case in years when spots were few and small. Applying corresponding processes to the meteorological records for St. Petersburg, he finds that a contrary state of things prevailed there. Next we have the evidence of the Rev. R. Main, director of the Radcliffe Observatory at Oxford, who finds that westerly winds are slightly more common when sun-spots are numerous than at other times. And lastly, Mr. Meldrum, of Mauritius, notes that years of spot-frequency are characterized on the whole by a greater number of storms and hurricanes, than years when the sun shows few spots.

The association between the sun-spot period and terrestrial magnetism is of a far more marked character, though I must premise that the Astronomer Royal, after careful analysis of the Greenwich magnetic records, denies the existence of any such association whatever. There is, however, a balance of evidence in its favor. It seems very nearly demonstrated that the daily sway of the magnetic needle is greatest when sun-spots are numerous, that magnetic storms are somewhat more numerous at such times, and that auroras also are more commonly seen. Now it has been almost demonstrated by M. Marié Davy, chief of the meteorological division in the Paris Observatory, that the weather is affected in a general way by magnetic disturbances. So that we are confirmed in the opinion that indirectly, if not directly, the weather is affected to some slight degree by the great sun-spot period.

Still I must point out that not one of these cases of agreement has anything like the evidence in its favor which had been found for an association between the varying distance of Jupiter and the sunspot changes. For eight consecutive maxima and minima this association has been strongly marked, and might be viewed as demonstrated,-only it chances unfortunately that for two other cases the relation is precisely reversed; and in point

of fact, whereas the period now assigned to the great sun-spot wave is eleven years and rather less than one month, Jupiter's period of revolution is eleven years and about ten months, a discrepancy of nine months, which would amount up to five and a half years (or modify perfect agreement into perfect disagreement) in seven or eight cycles.

But accepting the association between weather and the sun-spot changes as demonstrated (which is granting a great deal to the believers in solar weather-prediction), have we any reason to believe that by a long-continued study of the sun the great problem of foretelling the weather can be solved? This question, as I have already pointed out, must not be hastily answered. It is one of national, nay, of cosmopolitan importance. If answered in the affirmative, there is scarcely any expense which would be too great for the work suggested; but all the more careful must we be not to answer it in the affirmative, if the true answer should be negative.

But it appears to me that so soon as the considerations dealt with above have been fairly taken into account, there can be no possible doubt or difficulty in replying to the question. The matter has in effect, though not in intention, been tested experimentally, and the experiments, when carried out under the most favorable conditions, have altogether failed. To show that this is so, I take the position of affairs before Schwabe began that fine series of observations which ended in the discovery of the great spot-period of eleven years. Let us suppose that at that time the question had been mooted whether it might not be possible, by a careful study of the sun, to obtain some means of predicting the weather. The argument would then have run as follows:-"The sun is the great source of light and heat; that orb is liable to changes which must in all probability affect the supply of light and heat; those changes may be periodical and so predictable; and as our weather must to some extent depend on the supply of light and heat, we may thus find a means of predicting weather changes." The inquiry might then have been undertaken, and undoubtedly the great spot-period would have been detected, and with this discovery would have come that partial power of predicting the sun's condition which we now possess,

—that is, the power of saying that in such and such a year, taken as a whole, spots will be numerous or the reverse. Moreover, meteorological observations conducted simultaneously would have shown that, as the original argument supposed, the quantity of heat supplied by the sun varies to a slight degree with the varying condition of the sun. Corresponding magnetic changes would be detected; and also those partial indications of a connection between phenomena of wind and rain and the sun's condition which have been indicated above. All this would be exceedingly interesting to men of science. But,-supposing all this had been obtained at the nation's expense, and the promise had been held out that the means of predicting weather would be the reward, the non-scientific tax-paying community might not improbably inquire what was the worth of these discoveries to the nation or to the world at large. Be it understood that I am not here using the cui bono argument. As a student of science, I utterly repudiate the notion that before scientific researches are undertaken, it must be shown that they will pay. But it is one thing to adopt this mean and contemptible view of scientific research, and quite another to countenance projects which are based ab initio upon the ground that they will more than repay their cost. Now, I think, if the nation made the inquiry above indicated, and under the circumstances mentioned, it would be very difficult to give a satisfactory reply. The tax-payers would say, "We have supplied so many thousands of pounds to found national observatories for the cultivation of the physics of science, and we have paid so many thousands of pounds yearly to the various students of science who have kindly given their services in the management of these observatories; let us hear what are the utilitarian results of all this outlay? We do not want to hear of scientific discoveries, but of the promised means of predicting the weather." The answer would be, "We have found that storms in the tropics are rather more numerous in some years than others, the variations having a period of eleven years; we can assert pretty confidently that auroras follow a similar law of frequency; south-west winds blow more commonly at Oxford, but less commonly elsewhere, when the sun-spots, following the eleven

year period, are at a maximum; and more rain falls with south-westerly winds than with south-easterly winds at Oxford and elsewhere, but less at St. Petersburg and elsewhere, when sun-spots are most numerous, while the reverse holds when the spots are rare." I incline to think that on being further informed that these results related to averages only, and gave no means of predicting the weather for any given day, week, or month, even as respects the unimportant points here indicated, the British tax-payer would infer that he had thrown away his money. I imagine that the army of observers who had gathered these notable results would be disbanded rather unceremoniously, and that for some considerable time science (as connected, at any rate, with promised "utilitarian" results) would stink in the nostrils of the nation.

But this is very far, indeed, from being all. Nay, we may almost say that this is nothing. Astronomers know the great spot period; they have even ascertained the existence of longer and shorter periods less marked in character; and they have ascertained the laws according to which other solar features besides the spots vary in their nature. It is certain that whatever remains to be discovered must be of a vastly less marked character. If then the discovery of the most striking law of solar change has led to no results having the slightest value in connection with the problem of weather-prediction, if periodic solar changes of a less marked character have been detected which have no recognisable bearing on weather changes, what can be hoped from the recognition of solar changes still more recondite in their nature? It is incredible that the complex phenomena involved in meteorological relations regarded as a whole, those phenomena which are but just discernibly affected by the great sun-spot period, should respond to changes altogether insignificant even when compared with the development and decay of a single small sun-spot. It appears to me, therefore, that it is the duty of the true lover of science to indicate the futility of the promises which have been mistakenly held out; for it cannot be to the credit of science, or ultimately to its advantage, if government assistance be obtained on false pretences for any branch of scientific research.-St. Paul's Magazine.