Part 1

_ROUGH WAYS MADE SMOOTH_

ROUGH WAYS MADE SMOOTH

A SERIES OF

Familiar Essays on Scientific Subjects

BY RICHARD A. PROCTOR

_NEW IMPRESSION_

LONGMANS, GREEN, AND CO.

39 PATERNOSTER ROW, LONDON

NEW YORK AND BOMBAY

1903

_All rights reserved_

'_Let knowledge grow from more to more_'

TENNYSON

PREFACE.

It is scarcely necessary for me to explain the plan of the present work, because I have already--in introducing my 'Light Science for Leisure Hours,' my 'Science Byways,' and my 'Pleasant Ways in Science'--described the method on which, as I think, such treatises as the present should be written. This work deals with similar subjects in a similar way; but I think the experience I have acquired in writing other works on the same plan has enabled me to avoid some defects in the present work which I have recognised in the others.

The list of subjects indicates sufficiently the range over which the present volume extends. Some of them might be judged by their names to be in no way connected with science, but it will be found that none have been treated except in their scientific significance, though in familiar and untechnical terms.

RICHARD A. PROCTOR.

S.S. 'ARIZONA,' IRISH SEA _October 18, 1879._

CONTENTS.

PAGE THE SUN'S CORONA AND HIS SPOTS 1

SUN-SPOTS AND COMMERCIAL PANICS 26

NEW PLANETS NEAR THE SUN 32

RESULTS OF THE BRITISH TRANSIT EXPEDITIONS 58

THE PAST HISTORY OF OUR MOON 81

A NEW CRATER IN THE MOON 98

THE NOVEMBER METEORS 111

EXPECTED METEOR SHOWER 117

COLD WINTERS 125

OXFORD AND CAMBRIDGE ROWING 148

ROWING STYLES 169

ARTIFICIAL SOMNAMBULISM 178

HEREDITARY TRAITS 205

BODILY ILLNESS AS A MENTAL STIMULANT 236

DUAL CONSCIOUSNESS 259

ELECTRIC LIGHTING 289

ROUGH WAYS MADE SMOOTH.

_THE SUN'S CORONA AND HIS SPOTS._

One of the most important results of observations made upon the eclipse of July 29, 1878, indicates the existence of a law of sympathy, so to speak, between the solar corona and the sun-spots. The inquiry into this relation seems to me likely to lead to a very interesting series of researches, from which may possibly result an interpretation not only of the relation itself, should it be found really to exist, but of the mystery of the sun-spot period. I speak of the sun-spot period as mysterious, because even if we admit (which I think we cannot do) that the sun-spots are produced in some way by the action of the planets upon the sun, it would still remain altogether a mystery how this action operated. When all the known facts respecting the sun-spots are carefully considered, no theory yet advanced respecting them seems at all satisfactory, while no approach even has been made to an explanation of their periodic increase and diminution in number. This seems to me one of the most interesting problems which astronomers have at present to deal with; nor do I despair of seeing it satisfactorily solved within no very long interval of time. Should the recognition of a sympathy between the corona and the sun-spots be satisfactorily established, an important step in advance will have been made,--possibly even the key to the enigma will be found to have been discovered.

I propose now to consider, first, whether the evidence we have on this subject is sufficient, and afterwards to discuss some of the ideas suggested by the relations which have been recognised as existing between the sun-spots, the sierra, the coloured prominences, and the zodiacal light.

The evidence from the recent eclipses indicates beyond all possibility of doubt or question, that during the years when sun-spots were numerous, in 1870 and 1871, the corona, at least on the days of the total solar eclipses in those years, presented an appearance entirely different from that of the corona seen on July 29, 1878, when the sun was almost free from spots. This will be more fully indicated further on. At present it is necessary to notice only (1) that whereas in 1870 and 1871 the inner corona extended at least 250,000 miles from the sun, it reached only to a height of some 70,000 miles in 1878; (2) in 1870 and 1871 it possessed a very complicated structure, whereas in 1878 the definite structure could be recognised only in two parts of the inner corona; (3) in 1871 the corona was pink, whereas in 1878 it was pearly white; (4) the corona was ten times brighter in 1871 than in 1878; lastly, in 1871 the light of the corona came in part from glowing gas, whereas in July, 1878, the light came chiefly, if not wholly, from glowing solid or liquid matter. I must here point out, that the evidence of change, however satisfactory in itself, would be quite insufficient to establish the general theory that the corona sympathises with the solar photosphere in the special manner suggested by the recent eclipse observations. There are few practices more unscientific, or more likely to lead to erroneous theorising, than that of basing a general theory on a small number of observations. In this case we have, in fact, but a single observed correspondence, though the observations establishing it form a series. It has been shown that so far as the special sun-spot period from the minimum of 1867 to the minimum of 1878 is concerned, there has been a certain correspondence between the aspect of the corona and the state of the sun's surface, with regard to spots. To assume from that single correspondence that the corona and the sun-spots are related in the same way, would be hazardous in the extreme. We may indeed find, when we consider other matters, that the probability of a general relation of this sort existing is so great antecedently, that but slight direct evidence would be required to establish the existence of the relation. But it must be remembered that before the eclipse of 1878 was observed, with the special result I have noticed, few were bold enough to assert the probable existence of any such relationship; and certainly no one asserted that the probability was very strong. I believe, indeed, that no one spoke more definitely in favour of the theory that the corona probably sympathises with the sun-spots than I did myself before the recent eclipse; but certainly I should not then have been willing to say that I considered the evidence very strong.

We must then look for evidence of a more satisfactory kind.

Now, although during the two centuries preceding the invention of the spectroscope and the initiation of the solar physical researches now in progress, observations of eclipses were not very carefully conducted, yet we have some records of the appearance of the corona on different occasions, which, combined with the known law of sun-spot periodicity, may enable us to generalise more safely than we could from observations during the present spot-period, though these observations have been far more exact than the older ones. I propose to examine some of these. Necessarily I must make some selection. I need hardly say that even if there were no such relation as that which seems to be indicated by recent observations, and if my purpose were simply to prove, either that such a relation exists or that it does not, I could very readily bring before the reader of these pages what would seem like the most satisfactory evidence that the relation is real. I must ask him to believe, however, that my purpose is to ascertain where the truth lies. I shall neither introduce any observation of the corona because it seems specially favourable to the theory that the corona sympathises with the photosphere, nor omit any, because it seems definitely opposed to that theory. To prevent any possibility of being unconsciously prejudiced, I shall take a series of coronal observations collected together by myself, on account of their intrinsic interest, several years ago, when I had not in my thoughts any theory respecting periodic changes in the corona--the series, namely, which is included in the sixth chapter of my treatise on the sun. Each of these observations I shall consider in connection with the known condition of the sun as to spots, and those results which seem to bear _clearly_, whether favourably or unfavourably, on the theory we are enquiring into, I shall bring before the reader.

Kepler, whose attention had been specially drawn to the subject of the light seen round the sun during total eclipse, by certain statements which Clavius had made respecting the eclipse of 1567, describes the eclipse of 1605 in the following terms:--'The whole body of the sun was completely covered for a short time, but around it there shone a brilliant light of a reddish hue and uniform breadth, which occupied a considerable portion of the heavens.' The corona thus seen may fairly be assumed to have resembled in extent that of 1871. A bright corona, reaching like that seen during the eclipse of July 1878 to a height of only about 70,000 miles from the sun's surface, would certainly not have been described by Kepler as occupying a considerable portion of the heavens, for a height of 70,000 miles would correspond only to about a twelfth of the sun's diameter; and a ring so narrow would be described very differently. It seems, then, that in 1605 a corona was seen which corresponded with that observed when the sun has had many spots on his surface. Now we have no record of the condition of the sun with regard to spots in 1605; but we know that the year 1615 was one of many spots, and the year 1610 one of few spots; whence we may conclude safely that the year 1605 was one of many spots. This case then is in favour of the theory we are examining.

In passing we may ask whether the observation by Clavius which had perplexed Kepler, may not throw some light on our subject. Clavius says that the eclipse of 1567 which should have been total was annular. The usual explanation of this has been that the corona was intensely bright close to the sun. And though Kepler considered that his own observation of a broad reddish corona satisfactorily removed Clavius's difficulty, it seems tolerably clear that the corona seen by Clavius must have been very unlike the corona seen by Kepler. In fact the former must have been like the corona seen in July, 1878, much smaller than the average, but correspondingly increased in lustre. Now with regard to the sun-spot period we can go back to the year 1567, though not quite so securely as we could wish. Taking the average sun-spot period at eleven years, and calculating back from the minimum of spots in the year 1610, we get four years of minimum solar disturbance, 1599, 1588, 1577, and 1566. We should have obtained the same result if we had used the more exact period, eleven one-ninth years, and had taken 1610·8 for the epoch of least solar disturbance (1610·8 meaning about the middle of October, 1610). Thus the year 1567 was a year of few sun-spots, probably occupying almost exactly the same position in the sun spot period as the year 1878. Clavius's observation, then, is in favour of our theory.

But another observation between Clavius's and Kepler's may here be noticed. Jensenius, who observed the eclipse of 1598 at Torgau in Germany, noticed that, at the time of mid-totality, a bright light shone round the moon. On this occasion, remarks Grant, the phenomenon was generally supposed to arise from a defect in the totality of the eclipse, though Kepler strenuously contended that such an explanation was at variance with the relation between the values of the apparent diameters of the sun and moon as computed for the time of the eclipse by aid of the solar and lunar tables. The corona, then, must have resembled that seen by Clavius, and since the year 1598 must have been very near the time of fewest spots, this observation accords with the theory we are examining.

The next observation is that made by Wyberd during the eclipse of 1652. Here there is a difficulty arising from the strange way in which the sun-spots behaved during the interval from 1645 to 1679. According to M. Wolf, whose investigation of the subject has been very close and searching, there was a maximum of sun-spots in 1639 followed by a minimum in 1645, the usual interval of about six years having elapsed; but there came a maximum in 1655, ten years later, followed by a minimum in 1666, eleven years later, so that actually twenty-one years would seem to have elapsed between successive minima (1645 and 1666). Then came a maximum in 1675, nine years later, and a minimum in 1679, four years later. Between the maxima of 1639 and 1675, including two spot periods, an interval of thirty-six years elapsed. There is no other instance on record, so far as I know, of so long an interval as this for two spot-periods. In passing, I would notice how little this circumstance accords with the theory that the sun-spots follow an exact law, or that from observations of the sun, means can ever be found for forming a trustworthy system of weather prediction, even if we assumed (which has always seemed to me a very daring assumption), that terrestrial weather is directly dependent on the progress of the sun-spot period. But here the irregularity of the spot changes affects us only as preventing us from determining or even from guessing what may have been the condition of the sun's surface in the year 1652. This year followed by seven years a period of minimum disturbance, and preceded by three years a period of maximum disturbance; but it would be unsafe to assume that the sun's condition in 1652 was nearer that of maximum than that of minimum disturbance. We must pass over Wyberd's observations of the corona in 1652, at least until some direct evidence as to the sun's condition shall have been obtained from the papers or writings of the observers of that year. I note only that Wyberd saw a corona of very limited extent, having indeed a height not half so great as that of many prominences which have been observed during recent eclipses. If the theory we are examining should be established beyond dispute, we should be led to infer that the year 1652 was in reality a year of minimum solar disturbance. Perhaps by throwing in such a minimum between 1645 and 1666, with of course a corresponding maximum, the wild irregularity of the sun-spot changes between 1645 and 1679 would be to some degree diminished.

We are now approaching times when more satisfactory observations were made upon the corona, and when also we have more complete records of the aspect of the sun's surface.

In 1706 Plantade and Capies saw a bright ring of white light extending round the eclipsed sun to a distance of about 85,000 miles, but merging into a fainter light, which extended no less than four degrees from the eclipsed sun, fading off insensibly until its light was lost in the obscure background of the sky. This corresponds unmistakably with such a corona as we should expect only to see at a time of many sun-spots, if the theory we are examining is sound. Turning to Wolf's list, we find that the year 1705 is marked as a year of maximum solar disturbance, and the year 1712 as that of the next minimum. Therefore 1706 was a year of many sun-spots--in fact, 1706 may have been the year of actual maximum disturbance, for it is within the limits of doubt indicated by Wolf. Certainly a corona extending so far as that which Plantade and Capies saw would imply an altogether exceptional degree of solar disturbance, if the theory we are considering is correct.

In 1715 Halley gave the following description of the corona:--'A few seconds before the sun was all hid, there discovered itself round the moon a luminous ring about a digit' (a twelfth) 'or perhaps a tenth part of the moon's diameter in breadth. It was of a pale whiteness or rather pearl colour, seeming to me a little tinged with the colours of the Iris, and to be concentric with the moon.' He added that the ring appeared much whiter and brighter near the body of the moon than at a distance from it, and that its exterior boundary was very ill-defined, seeming to be determined only by the extreme rarity of the luminous matter. The French astronomer Louville gave a similar account of the appearance of the ring. He added, however, that 'there were interruptions in its brightness, causing it to resemble the radial glory with which painters encircle the heads of the saints.' The smallness of the corona on this occasion corresponds with the description of the corona seen in July 1878; and though Louville's description of gaps is suggestive of a somewhat different aspect, yet, on the whole, the corona seen in 1715 more closely resembles one which would be seen at a time of minimum solar disturbance, if our theory can be trusted, than one which would be seen at a time of maximum disturbance. Wolf's list puts the year 1712 as one of minimum disturbance, with one year of doubt either way, and the middle of the year 1817 as the epoch of maximum disturbance, with a similar range of uncertainty. The case, then, is doubtful, but on the whole inclines to being unfavourable. I may remark that because of its unfavourable nature, I departed from the rule I had set myself, of taking only the cases included in my treatise on the sun. For the corona of 1715 is not described in that treatise, as indeed affording no evidence respecting this solar appendage. The evidence given in this case is probably affected in some degree by the unfavourable atmospheric conditions under which Halley certainly, and Louville probably, observed the eclipse. In any case the evidence is not strong; only I would call attention here to the circumstance that if, as we proceed, we _should_ come to a case in which the evidence is plainly against the theory we are examining, we must give up the theory at once. For one case of discordance does more to destroy a theory respecting association between such and such phenomena, than a hundred cases of agreement would do in the way of confirming it.

In 1724, Maraldi noticed that the corona was broadest first on the side towards which the moon was advancing, and afterwards on the side which the moon was leaving. From this we may infer that the corona was only a narrow ring on that occasion, since otherwise the slight difference of breadth due to the moon's eccentric position at the beginning and end of totality would not have been noticeable. Now, the year 1723 was one of minimum disturbance, with one year of doubt either way. Thus 1724 was certainly a year of few sun-spots, and may have been the actual year of minimum disturbance. The corona then presented an appearance according with the theory we are considering.

Few eclipses have been better observed than that of the year 1733. The Royal Society of Sweden invited all who could spare the time to assist, as far as their ability permitted, in recording the phenomena presented during totality. The pastor of Stona Malm states that at Catherinesholm, there was a ring around the sun about 70,000 miles in height. (Of course these are not his exact words; what he actually stated was that the ring was about a digit in breadth.) This is the exact height assigned to the coronal ring by the observers of the eclipse of last year. The ring seemed to be of a reddish colour. Another clergyman, Vallerius, states also that the ring was of this colour, but adds that at a considerable distance from the sun it had a greenish hue. This suggests the idea that the outer corona was seen also by Vallerius, and that it had considerable breadth. The reddish colour of the inner light portion would correspond to the colour it would have if it consisted in the main of glowing hydrogen. If that really was its constitution, then the theory advanced by one observer of the last eclipse, that at the time of minimum solar disturbance the glowing hydrogen is withdrawn from the corona, would be shown to be incorrect. For 1733 was the actual year of minimum solar disturbance. The pastor of Smoland states that 'during the total obscuration the edge of the moon's disc resembled gilded brass, and the faint ring round it emitted rays in an upward as well as in a downward direction, similar to those seen beneath the sun when a shower of rain is impending.' The mathematical lecturer of the Academy of Charles-stadt, M. Edstrom, observed these rays with special attention: he says that 'they plainly maintained the same position, until they vanished along with the ring upon the re-appearance of the sun.' On the other hand, at Lincopia no rays were seen. On the whole it seems clear from the accounts of this eclipse that the inner corona was bright and narrow; rays issued from the outer faint ring; but they were very delicate phenomena, easily concealed by atmospheric haze, and thus were not everywhere observed. As rays were seen in July 1878, there is nothing in the evidence afforded by the eclipse of 1733, occurring at a time of few spots, which opposes itself definitely to the theory we are considering. But the reddish colour of the corona as already noticed is a doubtful feature: in July, 1878, the bright inner corona was of a pearl colour and lustre.

During the eclipse of February, 1766, the corona presented four luminous expansions, and seems to have presented a greater expansion than we should expect in a year of minimum solar disturbance. Such, however, the year 1766 certainly was. The evidence in this case is unfavourable to our theory--not quite decisively so, but strongly. For we should expect that in the year of actual minimum disturbance the corona would be even narrower than in the year 1878, which was the year following that of least disturbance. And again, a strongly distinctive feature in the corona of July, 1878, was the absence of wide expansions, such as were seen in 1870 and 1871. Now if this peculiarity should really be attributed to the relation existing between the corona and the sun-spots, we should infer that in 1766 the corona would have been still more markedly uniform in shape. The existence of four well marked expansions on that occasion forces us to assume that either the relation referred to has no real existence, or else that the corona may change from week to week as the condition of the sun's surface changes, and that in February, 1766, the sun was temporarily disturbed, though the year, as a whole, was one of minimum disturbance. But as the epoch of actual minimum was the middle of 1766, February 1766 should have been a time of very slight disturbance. I do not know of any observations of the sun recorded for the month of February, 1766. On the whole, the eclipse of 1766 must be regarded as throwing grave doubt on the relation assumed by our theory as existing between the corona and the sun-spots; and as tending to suggest that some wider law must be in question than the one we have been considering--if any association really exists.