Nov. 1 8, 1886] 



NATURE 



69 



The Sun and Met€oroloi;y. — The study of tlie solar surface has 

 been carried on very persistently by Sptirer, in Germany, as 

 well as by others, and a great a uount of material has been col- 

 lected bearing upon the theory and nature of sunspots, and their 

 periodicity. The extensive series of photographs obtained at 

 Kew, and at Dehra Doon, in India, constitutes almost a con- 

 tinuous record of the solar surface for several years. The rela- 

 tion between this periodicity and terrestrial conditions has been 

 assiduously examined, but on the whole the outcome seems to 

 me to leave this connection as doubtful as it ever was, in most 

 cases at least. While in some parts of the earth it looks as if 

 there were a slight but marked increase of storm and rainfall at 

 the time of sunspot maximum, the reverse seems to be true in 

 other countries. In South America, Dr. Gould thinks that he 

 has demonstrated a very perceptible efiect of the condition of 

 the sun's surface in modifying the strength and direction of the 

 winds ; but thus far similar investigations elsewhere show no 

 such result. It will evidently be necessary to wait for a longer 

 and more widely extended collection of statistics to settle the 

 question. We do not even know as yet whether we get more 

 or less than the average heat from the sun during the sunspot 

 maximum. 



But I think it may be set down as certain that the condition 

 of the sun's surface exerts, if perhaps a real, yet only a very slight 

 effect upon oar earthly meteorology. With terrestrial magnetism 

 the case is markedly and singularly different, and one of the 

 most interesting problems now pressing for solution is the nature 

 of the connection between solar disturbances and magnetic 

 storms. 



Solar Heat. — A great deal of labour has been expended upon 

 the study of the sun's heat during the last decade. The in- 

 vestigations that strike me on the whole as most worthy of 

 mention are those of our own Langley and of the Italian Rosetti, 

 whose early death a few months ago is a great loss to science. 

 Secchi and Ericsson, on the one side, had contended for a 

 solar temperature of some millions of degrees, basing their 

 results on Newton's law of cooling ; while, on the other, Crova 

 and Violle, from their measures of the solar radiation, reduced 

 according to the so-called law of Didong and Petit, maintained 

 that the temperature does not much exceed that of many ter- 

 restrial furnaces, somewhere from 1500° to 2500° C. Kosetti's 

 experiments upon the radiation of the electric arc and other 

 sources of intense heat showed pretty clearly the inapplicability 

 of Dulong and Petit's law to high temperatures, and indicate a 

 solar temperature not far from 10,000° C., or 18,000° F. But 

 they also make it clear that the limits of uncertainty are still 

 very great. 



Prof. Langley, by his invention of the bolometer, has been 

 able to investigate separately the amount of energy transmitted 

 to the earth in the solar rays of every possible wave-length, and 

 to determine the effect of our atmosphere in absorbing each kind 

 of ray. He has shown that the older method of investigating 

 this solar radiation, in a lump so to speak, gives fallacious 

 results on account of atmospheric absorption ; and that the 

 necessary correction compels us to increase our estimate of the 

 sun's energy at least 20 per cent. In my own little book upon 

 the sun, published in 1S81, I had set the so-called solar con- 

 stant at twenty-five calories per square metre per minute. It is 

 now certain that it must be put at least as high as thirty. Prof. 

 Langley's investigations seem also to show another remarkable 

 fact — that we do not receive from the sun any at all of the low- 

 pitched, slowly-pulsing waves, such as we get from surfaces at 

 or below the temperature of boiling water. The solar spectrum 

 appears to be cut off abruptly at the lower end ; and this cutting 

 off we know cannot have been effected in the earth's atmosphere, 

 because we receive from the moon in considerable quantity just 

 this very sort of low-pitched rntys. Langley finds them also 

 abundant in the radiation of the electric arc, so that we can 

 hardly suppose them to be originally wanting in the solar heat. 

 It now looks as if we must admit that they have been suppressed 

 either in the atmosphere of the sun itself, or in interplanetary 

 space. Another striking conclusion first clearly pointed out by 

 Langley is that, if the sun's atmosphere were removed, its light 

 would be strongly blue. 



The Solar Surface and Spots. — As regards the general make- 

 up of the solar surface, I do not think there has been any new 

 fact of extreme importance brought out within ten years. Janssen 

 has, however, carried solar photography to higher excellence 

 than ever attained before, and has obtained plates that show the 

 " granules " and their grouping on a scale previously unknown. 



He thinks that his plates prove a peculiar constitution of the 

 solar surface, consisting in collections of clearly-defined and 

 rounded granules, separated by regions or streaks where they 

 ate ill defined and elongated ; and he calls the phenomenon the 

 " reseau photospherique," or photospheric network. According 

 to him the "net" remains approximately constant for some 

 minutes at a time, as shown by plates taken in quick succession, 

 but is subject to rapid and enormous changes in periods exceed- 

 ing a quarter of an hour or so. I find some scepticism among 

 high authorities as to the trustworthiness of his conclusions. 

 There are suggestions that the appearances presented may be 

 due to currents of air in the telescope tube and at the surface of 

 the sensitive plate ; but I am disposed to think he is right, for, 

 on several occasions when the seeing has been exceptionally fine, 

 I have observed with my own eyes something quite analogous, 

 in our large telescope at Princeton. 



The spots have been carefully studied by several observers, by 

 Sporer especially, in a statistical way, and by Vogel, I^ohse, 

 Tacchini, and others, as to 'structure and detail. Sporer has 

 brought out very clearly the connection between the number and 

 average latitude of the spots. It appears that, speaking broadly, 

 the disturbance which produces the sunspots begins in two belts 

 on each side of the sun's equator in a latitude of over 30' ; these 

 belts or spot-zones then gradually move in towards the equator, 

 the sunspot maximum occurring when their latitude is about 

 16", while the disturbance gradually and finally disappears at 

 a latitude of 8° or 10°, some twelve or fourteen years after its 

 first appearance. But two or three years before this disappear- 

 ance a new zone of disturbance shows itself in the same latitude 

 as its predecessor, so that for a while, about the time of sun- 

 spot minimum, there are two well-marked zones of spots on each 

 side of the sun's equator — one pair near the equator, due to the 

 expiring disturbance which began some ten or eleven years ago ; 

 the other far from the equator, and due to the newly-arising out- 

 burst, which will reach its maximum in three or four years, and 

 then pass away like the former. 



There can be no doubt that the phenomenon is a very sig- 

 nificant one, but its explanation, like that of the periodicity 

 itself, is still to be found. 



Nor is the problem of the spots themselves yet fully solved. 

 Not that there is any reasonable question that they are hollows 

 in the solar photosphere ; but how they originate, how deep 

 they are, and what are the causes of their darkness, and the 

 condition and temperature of the darkening substance — -these are 

 questions to which only uncertain answers can now be given. A 

 long and important series of observations upon the widening of 

 the lines of certain elements in the sunspot spectra has been 

 made by Mr. Lockyer, and establishes clearly the fact that those 

 lines, of iron for instance, which are conspicuously black and 

 wide in the sunspots, are often just those which do not show 

 themselves conspicuously in the prominences ; and moreover 

 both in spots and prominences the iron lines that do show them- 

 selves are most frequently those which closely coincide with 

 lines in the spectra of other substances. Singularly, also, and 

 so far quite without explanation, it appears according to his 

 observations that at the sunspot maximum those iron lines 

 which at other times are conspicuous in spot-spectra entirely 

 disappear. 



Peihaps I may be allowed to mention here a recent observa- 

 tion of my own upon these spot-spectra : with a high dispersion 

 the darkest part of the spot-spectrum is found to be not con- 

 tinuous, but made up of fine lines overlapping or almost touching 

 each other, with here and there a clear space left, like a fine 

 bright line. It means, I think, that the absorbing vapours 

 which darken the interior of the spot are wholly gaser us, and 

 tends to disprove the idea that they are mostly of the nature of 

 smoke or steam. We mention also, in passing, another thing 

 which has been shown by our large instrument at Princeto.i — 

 that the apparently bulbous, finger-tip-like terminations of the 

 penurabral filaments are often, under the best circumstances of 

 vision, resolved into fine, bright, sharp-pointed hooks which look 

 like the tips of curling flames. 



(Ti; Oc continued.) 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 

 Cambridge. — At the biennial election of members of the 

 Council of the Senate, Prof. iVIich.ael Foster and Dr. Donald 

 MacAlister were elected to serve for four years. 



