Chapter XII. Fossils found in the peat bogs of Denmark and Scandinavia,

for example, prove that since the final disappearance of the continental ice cap at the close of the Wisconsin there has been at least one period when the climate of Europe was distinctly milder than now. Directly overlying the sheets of glacial drift laid down by the ice there is a flora corresponding to that of the present tundras. Next come remains of a forest vegetation dominated by birches and poplars, showing that the climate was growing a little warmer. Third, there follow evidences of a still more favorable climate in the form of a forest dominated by pines; fourth, one where oak predominates; and fifth, a flora similar to that of the Black Forest of Germany, indicating that in Scandinavia the temperature was then decidedly higher than today. This fifth flora has retreated southward once more, having been driven back to its present latitude by a slight recurrence of a cool stormy climate.[123] In central Asia evidence of post-glacial stages is found not only in five distinct moraines but in a corresponding series of elevated strands surrounding salt lakes and of river terraces in non-glaciated arid regions.[124]

In historic as well as prehistoric times, as we have already seen, there have been climatic fluctuations. For instance, the twelfth or thirteenth century B. C. appears to have been almost as mild as now, as does the seventh century B. C. On the other hand about 1000 B. C., at the time of Christ, and in the fourteenth century there were times of relative severity. Thus it appears that both on a large and on a small scale pulsations of climate are the rule. Any hypothesis of climatic changes must satisfy the periods of these pulsations. These conditions furnish a problem which makes difficulty for almost all hypotheses of climatic change. According to the present hypothesis, earth movements such as are discussed in Chapter XII may coöperate with two astronomical factors. One is the constant change in the positions of the stars, a change which we have already called kaleidoscopic, and the other is the fact that a large proportion of the stars are double or multiple. When one star in a group approaches the sun closely enough to cause a great solar disturbance, numerous others may approach or recede and have a minor effect. Thus, whenever the sun is near groups of stars we should expect that the earth would show many minor climatic pulsations and stages which might or might not be connected with glaciation. The historic pulsations shown in the curve of tree growth in California, Fig. 4, are the sort of changes that would be expected if movements of the stars have an effect on the solar atmosphere.

Not only are fully a third of all the visible stars double, as we have already seen, but at least a tenth of these are known to be triple or multiple. In many of the double stars the two bodies are close together and revolve so rapidly that whatever periodicity they might create in the sun's atmosphere would be very short. In the triplets, however, the third star is ordinarily at least ten times as far from the other two as they are from each other, and its period of rotation sometimes runs into hundreds or thousands of years. An actual multiple star in the constellation Polaris will serve as an example. The main star is believed by Jeans to consist of two parts which are almost in contact and whirl around each other with extraordinary speed in four days. If this is true they must keep each other's atmospheres in a state of intense commotion. Much farther away a third star revolves around this pair in twelve years. At a much greater distance a fourth star revolves around the common center of gravity of itself and the other three in a period which may be 20,000 years. Still more complicated cases probably exist. Suppose such a system were to traverse a path where it would exert a perceptible influence on the sun for thirty or forty thousand years. The varying movements of its members would produce an intricate series of cycles which might show all sorts of major and minor variations in length and intensity. Thus the varied and irregular stages of glaciation and the pulsations of historic times might be accounted for on the hypothesis of the proximity of the sun to a multiple star, as well as on that of the less pronounced approach and recession of a number of stars. In addition to all this, an almost infinitely complex series of climatic changes of long and short duration might arise if the sun passed through a nebula.

5. We have seen in Chapter VIII that the contrast between the somewhat severe climate of the present and the generally mild climate of the past is one of the great geological problems. The glacial period is not a thing of the distant past. Geologists generally recognize that it is still with us. Greenland and Antarctica are both shrouded in ice sheets in latitudes where fossil floras prove that at other periods the climate was as mild as in England or even New Zealand. The present glaciated regions, be it noted, are on the polar borders of the world's two most stormy oceanic areas, just where ice would be expected to last longest according to the solar cyclonic hypothesis. In contrast with the semi-glacial conditions of the present, the last inter-glacial epoch was so mild that not only men but elephants and hippopotamuses flourished in central Europe, while at earlier times in the middle of long eras, such as the Paleozoic and Mesozoic, corals, cycads, and tree ferns flourished within the Arctic circle.

If the electro-stellar hypothesis of solar disturbances proves well founded, it may explain these peculiarities. Periods of mild climate would represent a return of the sun and the earth to their normal conditions of quiet. At such times the atmosphere of the sun is assumed to be little disturbed by sunspots, faculæ, prominences, and other allied evidences of movements; and the rice-grain structure is perhaps the most prominent of the solar markings. The earth at such times is supposed to be correspondingly free from cyclonic storms. Its winds are then largely of the purely planetary type, such as trade winds and westerlies. Its rainfall also is largely planetary rather than cyclonic. It falls in places such as the heat equator where the air rises under the influence of heat, or on the windward slopes of mountains, or in regions where warm winds blow from the ocean over cold lands.

According to the electro-stellar hypothesis, the conditions which prevailed during hundreds of millions of years of mild climate mean merely that the solar system was then in parts of the heavens where stars--especially double stars--were rare or small, and electrical disturbances correspondingly weak. Today, on the other hand, the sun is fairly near a number of stars, many of which are large doubles. Hence it is supposed to be disturbed, although not so much as at the height of the last glacial epoch.

After the preceding parts of this book had been written, the assistance of Dr. Schlesinger made it possible to test the electro-stellar hypothesis by comparing actual astronomical dates with the dates of climatic or solar phenomena. In order to make this possible, Dr. Schlesinger and his assistants have prepared Table 6, giving the position, magnitude, and motions of the thirty-eight nearest stars, and especially the date at which each was nearest the sun. In column 10 where the dates are given, a minus sign indicates the past and a plus sign the future. Dr. Shapley has kindly added column 12, giving the absolute magnitudes of the stars, that of the sun being 4.8, and column 13, showing their luminosity or absolute radiation, that of the sun being unity. Finally, column 14 shows the effective radiation received by the sun from each star when the star is at a minimum distance. Unity in this case is the effect of a star like the sun at a distance of one light year.

It is well known that radiation of all kinds, including light, heat, and electrical emissions, varies in direct proportion to the exposed surface, that is, as the square of the radius of a sphere, and inversely as the square of the distance. From black bodies, as we have seen, the total radiation varies as the fourth power of the absolute temperature. It is not certain that either light or electrical emissions from incandescent bodies vary in quite this same proportion, nor is it yet certain whether luminous and electrical emissions vary exactly together. Nevertheless they are closely related. Since the light coming from each star is accurately measured, while no information is available as to electrical emissions, we have followed Dr. Shapley's suggestion and used the luminosity of the stars as the best available measure of total radiation. This is presumably an approximate measure of electrical activity, provided some allowance be made for disturbances by outside bodies such as companion stars. Hence the inclusion of column 14.

TABLE 6

THIRTY-EIGHT STARS HAVING LARGEST KNOWN PARALLAXES

Star Code 1 Groombr. 34 2 ++[Greek: ê] Cassiop. 3 4 ++[Greek: k] Tucanæ 5 [Greek: t] Ceti 6 [Greek: d]_2 Eridani 7 ++[Greek: e] Eridani 8 ++40(0)^2 Eridani 9 Cordoba Z. 243 10 Weisse 592 11 ++[Greek: a] Can. Maj. (Sirius) 12 ++[Greek: a] Can. Min. (Procyon) 13 ++Fedorenko 1457-8 14 Groombr. 1618 15 Weisse 234 16 Lalande 21185 17 Lalande 21258 18 19 Lalande 25372 20 ++[Greek: a] Centauri 21 ++[Greek: x] Bootes 22 ++Lalande 27173 23 Weisse 1259 24 Lacaille 7194 25 ++[Greek: b] 416 26 Argel -0.17415-6 27 Barnard's star 28 ++70p Ophiuchi 29 ++[Greek: S] 2398 30 [Greek: s] Draconis 31 ++[Greek: a] Aquilæ (Altair) 32 ++61 Cygni 33 Lacaille 8760 34 [Greek: e] Indi 35 ++Krüger 60 36 Lacaille 9352 37 Lalande 46650 38 C. G. A. 32416

(++ Double star.)

(1) (2) (3) (4) (5) (6) Right Declination Visual Spectrum Proper Radial Star Ascension [Greek: d] Mag. m Motion Velocity code [Greek: a] 1900 km. per 1900 sec. ------------------------------------------------------------------ 1 0^h 12^m.7 +43°27' 8.1 Ma 2".89 + 3 2 43 .0 +57 17 3.6 F8 1 .24 + 10 3 43 .9 +4 55 12.3 F0 3 .01 ..... 4 1 12 .4 -69 24 5.0 F8 .39 + 12 5 39 .4 -16 28 3.6 K0 1 .92 - 16 ------------------------------------------------------------------ 6 3 15 .9 -43 27 4.3 G5 3 .16 + 87 7 28 .2 - 9 48 3.8 K0 .97 + 16 8 4 10 .7 - 7 49 4.5 G5 4 .08 - 42 9 5 7 .7 -44 59 9.2 K2 8 .75 +242 10 26 .4 - 3 42 8.8 K2 2 .22 ..... ------------------------------------------------------------------ 11 6 40 .7 -16 35 -1.6 A0 1 .32 - 8 12 7 34 .1 + 5 29 0.5 F5 1 .24 - 4 13 9 7 .6 +53 7 7.9 Ma 1 .68 + 10 14 10 5 .3 +49 58 6.8 K5p 1 .45 - 30 15 14 .2 +20 22 9.0 ... .49 ..... ------------------------------------------------------------------ 16 57 .9 +36 38 7.6 Mb 4 .78 - 87 17 11 0 .5 +44 2 8.5 K5 4 .52 + 65 18 12 .0 -57 2 12.0 ... 2 .69 ..... 19 13 40 .7 +15 26 8.5 K5 2 .30 ..... 20 14 32 .8 -60 25 0.2 G 3 .68 + 22 ------------------------------------------------------------------ 21 14 46 .8 +19 31 4.6 K5p .17 + 4 22 51 .6 -20 58 5.8 Kp 1 .96 + 20 23 16 41 .4 +33 41 8.4 ... .37 ..... 24 17 11 .5 -46 32 5.7 K .97 ..... 25 12 .1 -34 53 5.9 K5 1 .19 - 4 ------------------------------------------------------------------ 26 37 .0 +68 26 9.1 K 1 .33 ..... 27 52 .9 + 4 25 9.7 Mb 10 .30 - 80 28 18 0 .4 + 2 31 4.3 K 1 .13 ..... 29 41 .7 +59 29 8.8 K 2 .31 ..... 30 19 32 .5 +69 29 4.8 G5 1 .84 + 26 ------------------------------------------------------------------ 31 45 .9 + 8 36 1.2 A5 .66 - 33 32 21 2 .4 +38 15 5.6 K5 5 .20 - 64 33 11 .4 -39 15 6.6 G 3 .53 + 13 34 55 .7 -57 12 4.8 K5 4 .70 - 39 35 22 24 .4 +57 12 9.2 ... .87 ..... ------------------------------------------------------------------ 36 59 .4 -36 26 7.1 K 6 .90 + 12 37 23 44 .0 + 1 52 8.7 Ma 1 .39 ..... 38 59 .5 -37 51 8.2 G 6 .05 + 26

(7) (9) (11) (13) (14) Present Minimum Magnitude Luminosity Effective Parallax Distance at Min. Dist. | radiation [Greek: p] Light Yrs. | | at | | | | minimum | (8) | (10) | (12) | distance Star | Maximum | Time of | Absolute | from sun Code | Parallax | Minimum | Magnitude | | | | | Distance | | | | ----------------------------------------------------------------------- 1 ".28 ".28 11.6 -4000 8.1 10.3 0.0063 0.000051 2 .18 .19 17.1 -47000 3.5 4.9 0.91 0.003110 3 .24 .... .... ...... .... 14.2 0.00017 ........ 4 .16 .23 14.2 -264000 4.2 6.0 0.33 0.001610 5 .32 .37 8.8 +46000 3.3 6.1 0.30 0.003840 ----------------------------------------------------------------------- 6 .16 .22 14.8 -33000 3.6 5.3 0.63 0.002960 7 .31 .46 7.1 -106000 3.0 6.3 0.25 0.004970 8 .21 .23 14.2 +19000 4.3 6.1 0.30 0.001470 9 .32 .68 4.8 -10000 7.6 11.7 0.0017 0.000074 10 .17 .... .... ...... .... 9.9 0.009 ........ ----------------------------------------------------------------------- 11 .37 .41 8.0 +65000 -1.8 1.2 27.50 0.429000 12 .31 .32 10.2 +34000 0.5 3.0 5.25 0.051300 13 .16 .16 20.4 -24000 7.9 8.9 0.023 0.000055 14 .18 .23 14.2 +69000 6.3 8.1 0.048 0.000238 15 .19 .... .... ...... .... 10.4 0.0057 ........ ----------------------------------------------------------------------- 16 .41 .76 4.3 +20000 6.2 10.7 0.0044 0.000238 17 .19 .22 14.8 -20000 8.2 9.9 0.009 0.000041 18 .34 .... .... ...... .... 14.7 0.00011 ........ 19 .19 .... .... ...... .... 9.9 0.009 ........ 20 .76 1.03 3.2 -28000 -0.5 4.6 1.20 0.117500 ----------------------------------------------------------------------- 21 .17 .22 14.8 -598000 4.0 5.8 0.40 0.001815 22 .18 .19 17.1 -36000 5.6 7.1 0.12 0.000412 23 .18 .... .... ...... .... 9.7 0.011 ........ 24 .19 .... .... ...... .... 7.1 0.12 ........ 25 .17 .17 19.2 +21000 5.7 7.1 0.12 0.000329 ----------------------------------------------------------------------- 26 .22 .... .... ...... .... 10.8 0.004 ........ 27 .53 .70 4.7 +10000 9.1 13.3 0.0025 0.000114 28 .19 .... .... ...... .... 5.7 0.44 ........ 29 .29 .... .... ...... .... 11.1 0.0030 ........ 30 .20 .23 14.2 -49000 4.5 6.3 0.25 0.001238 ----------------------------------------------------------------------- 31 .21 .51 6.4 +117000 -0.7 2.8 6.30 0.153600 32 .30 .38 8.6 +19000 5.1 8.0 0.053 0.000715 33 .25 .26 12.6 -11000 6.6 8.6 0.030 0.000189 34 .28 .31 10.5 +17000 4.6 7.0 0.13 0.001230 35 .26 .... .... ....... .... 11.3 0.0025 ........ ----------------------------------------------------------------------- 36 .29 .29 11.2 -3000 7.1 9.4 0.014 0.000111 37 .17 .... .... ....... .... 9.9 0.009 ........ 38 .22 .22 14.8 -7000 8.2 9.9 0.009 0.000041 -----------------------------------------------------------------------

On the basis of column 14 and of the movements and distances of the stars as given in the other columns Fig. 10 has been prepared. This gives an estimate of the approximate electrical energy received by the sun from the nearest stars for 70,000 years before and after the present. It is based on the twenty-six stars for which complete data are available in Table 6. The inclusion of the other twelve would not alter the form of the curve, for even the largest of them would not change any part by more than about half of 1 per cent, if as much. Nor would the curve be visibly altered by the omission of all except four of the twenty-six stars actually used. The four that are important, and their relative luminosity when nearest the sun, are Sirius 429,000, Altair 153,000, Alpha Centauri 117,500, and Procyon 51,300. The figure for the next star is only 4970, while for this star combined with the other twenty-one that are unimportant it is only 24,850.

Figure 10 is not carried more than 70,000 years into the past or into the future because the stars near the sun at more remote times are not included among the thirty-eight having the largest known parallaxes. That is, they have either moved away or are not yet near enough to be included. Indeed, as Dr. Schlesinger strongly emphasizes, there may be swiftly moving, bright or gigantic stars which are now quite far away, but whose inclusion would alter Fig. 10 even within the limits of the 140,000 years there shown. It is almost certain, however, that the most that these would do would be to raise, but not obliterate, the minima on either side of the main maximum.

In preparing Fig. 10 it has been necessary to make allowance for double stars. Passing by the twenty-two unimportant stars, it appears that the companion of Sirius is eight or ten magnitudes smaller than that star, while the companions of Procyon and Altair are five or more magnitudes smaller than their bright comrades. This means that the luminosity of the faint components is at most only 1 per cent of that of their bright companions and in the case of Sirius not a hundredth of 1 per cent. Hence their inclusion would have no visible effect on Fig. 10. In Alpha Centauri, on the other hand, the two components are of almost the same magnitude. For this reason the effective radiation of that star as given in column 14 is doubled in Fig. 10, while for another reason it is raised still more. The other reason is that if our inferences as to the electrical effect of the sun on the earth and of the planets on the sun are correct, double stars, as we have seen, must be much more effective electrically than single stars. By the same reasoning two bright stars close together must excite one another much more than a bright star and a very faint one, even if the distances in both cases are the same. So, too, other things being equal, a triple star must be more excited electrically than a double star. Hence in preparing Fig. 10 all double stars receive double weight and each part of Alpha Centauri receives an additional 50 per cent because both parts are bright and because they have a third companion to help in exciting them.

According to the electro-stellar hypothesis, Alpha Centauri is more important climatically than any other star in the heavens not only because it is triple and bright, but because it is the nearest of all stars, and moves fairly rapidly. Sirius and Procyon move slowly in respect to the sun, only about eleven and eight kilometers per second respectively, and their distances at minimum are fairly large, that is, 8 and 10.2 light years. Hence their effect on the sun changes slowly. Altair moves faster, about twenty-six kilometers per second, and its minimum distance is 6.4 light years, so that its effect changes fairly rapidly. Alpha Centauri moves about twenty-four kilometers per second, and its minimum distance is only 3.2 light years. Hence its effect changes very rapidly, the change in its apparent luminosity as seen from the sun amounting at maximum to about 30 per cent in 10,000 years against 14 per cent for Altair, 4 for Sirius, and 2 for Procyon. The vast majority of the stars change so much more slowly than even Procyon that their effect is almost uniform. All the stars at a distance of more than perhaps twenty or thirty light years may be regarded as sending to the sun a practically unchanging amount of radiation. It is the bright stars within this limit which are important, and their importance increases with their proximity, their speed of motion, and the brightness and number of their companions. Hence Alpha Centauri causes the main maximum in Fig. 10, while Sirius, Altair, and Procyon combine to cause a general rise of the curve from the past to the future.

Let us now interpret Fig. 10 geologically. The low position of the curve fifty to seventy thousand years ago suggests a mild inter-glacial climate distinctly less severe than that of the present. Geologists say that such was the case. The curve suggests a glacial epoch culminating about 28,000 years ago. The best authorities put the climax of the last glacial epoch between twenty-five and thirty thousand years ago. The curve shows an amelioration of climate since that time, although it suggests that there is still considerable severity. The retreat of the ice from North America and Europe, and its persistence in Greenland and Antarctica agree with this. And the curve indicates that the change of climate is still persisting, a conclusion in harmony with the evidence as to historic changes.

If Alpha Centauri is really so important, the effect of its variations, provided it has any, ought perhaps to be evident in the sun. The activity of the star's atmosphere presumably varies, for the orbits of the two components have an eccentricity of 0.51. Hence during their period of revolution, 81.2 years, the distance between them ranges from 1,100,000,000 to 3,300,000,000 miles. They were at a minimum distance in 1388, 1459, 1550, 1631, 1713, 1794, 1875, and will be again in 1956. In Fig. 11, showing sunspot variations, it is noticeable that the years 1794 and 1875 come just at the ends of periods of unusual solar activity, as indicated by the heavy horizontal line. A similar period of great activity seems to have begun about 1914. If its duration equals the average of its two predecessors, it will end about 1950. Back in the fourteenth century a period of excessive solar activity, which has already been described, culminated from 1370 to 1385, or just before the two parts of Alpha Centauri were at a minimum distance. Thus in three and perhaps four cases the sun has been unusually active during a time when the two parts of the star were most rapidly approaching each other and when their atmospheres were presumably most disturbed and their electrical emanations strongest.

The fact that Alpha Centauri, the star which would be expected most strongly to influence the sun, and hence the earth, was nearest the sun at the climax of the last glacial epoch, and that today the solar atmosphere is most active when the star is presumably most disturbed may be of no significance. It is given for what it is worth. Its importance lies not in the fact that it proves anything but that no contradiction is found when we test the electro-stellar hypothesis by facts which were not thought of when the hypothesis was framed. A vast amount of astronomical work is still needed before the matter can be brought to any definite conclusion. In case the hypothesis stands firm, it may be possible to use the stars as a help in determining the exact chronology of the later part of geological times. If the hypothesis is disproved, it will merely leave the question of solar variations where it is today. It will not influence the main conclusions of this book as to the causes and nature of climatic changes. Its value lies in the fact that it calls attention to new lines of research.

FOOTNOTES:

[Footnote 120: Lewis Boss: Convergent of a Moving Cluster in Taurus; Astronom. Jour., Vol. 26, No. 4, 1908, pp. 31-36.]

[Footnote 121: F. R. Moulton: in Introduction to Astronomy, 1916.]

[Footnote 122: A. Penck: Die Alpen im Eiszeitalter, Leipzig, 1909.]

[Footnote 123: R. D. Salisbury: Physical Geography of the Pleistocene, in Outlines of Geologic History, by Willis and Salisbury, 1910, pp. 273-274.]

[Footnote 124: Davis, Pumpelly, and Huntington: Explorations in Turkestan, Carnegie Inst. of Wash., No. 26, 1905.

In North America the stages have been the subject of intensive studies on the part of Taylor, Leverett, Goldthwait, and many others.]