460 



NATURE 



\_August 29, 1878 



tion of the corona for polarisation, and this byabi-quartz 

 or a Savart polariscope, held in the hand so as to take in 

 the whole corona in one view. In the organisation of the 

 expedition, Dr. Hastings was requested to prepare a plan 

 by which the question as to whether the polarisation of 

 the corona was radial or tangential, or absent, could be 

 definitively settled. This was accomplished by an 

 arrangement of apparatus essentially novel. 



*' The four-inch telescope had a Savart polariscope at 

 its eye end. A diaphragm perforated with holes, 3', 4', 

 5', 8', 10', 16' was interposed between the polariscope and 

 the objective, and the polarisation phenomena of a defi- 

 nite and limited portion of the corona were thus seen. 

 Diaphragms of 3' and 5' were alone used. The telescope 

 was pointed by Lieut. Very to six points, the first one 

 above the sun and 50' from the circumference ; the 

 second one 25' from the circumference and 45° from the 

 vertical ; the third i^' from the sun and to the right of 

 it; the fourth 16' from the sun and to the right of it; 

 the fifth 16' from the sun and 135° from the vertical ; the 

 sixth 8' from the sun and 135° from the vertical. These 

 points were selected before the eclipse, but it was not known 

 to Dr. Hastings in what order they would be viewed, so 

 that the readings were absolutely free from bias. The 

 position of the pointer of the polariscope was carefully 

 verified before and after the totality. The readings were 

 reduced immediately, and each reading (which was, as 

 is evident, independent of every other) agreed in showing 

 that the plane of polarisation was perpendicular to the 

 sun's radius through the point examined— that is, tan- 

 ^ential — a most unexpected result, about which, however, 

 there is no doubt whatever. Four of the readings were 

 made with a dark band in the centre, and two with a 

 bright band. This result does not agree with others from 

 the same eclipse, for the reason that in the method 

 adopted by Prof. Morton, Mr. Lockyer, aad others, there 

 was, first, no means adopted for isolating a definite por- 

 tion of the corona and determining its special polarisa- 

 tion. Second, that in the use of the Savart form, the 

 phenomena of radial or tangential polarisation alike pre- 

 sent bands radial to the sun. Third, that, with the 

 bi-quartz, the field is so small that it becomes extremely 

 difficult to interpret the tints of colour seen, if indeed 

 any are seen. The novel fact was shown, by the use of 

 thi^ method, that the polarisation of the corona was ex- 

 ceedingly strong near to the sun's limb (one and a half 

 minutes), and was relatively weak far from it." 



I believe that no one is more astonished than Prof. 

 Hastings himself at the result of bis work, which, it has 

 been laughingly said, goes to demonstrate the existence 

 ice crystals in the corona. With reference to the 

 remarks made on my 1871 work in the foregoing, I may 

 add that I used a bi-quartz and a large field, so that the 

 objections raised to the method do not apply. 



This brings me to the end of my notes for the present 

 on the photographic, spectroscopic, and polariscopic 

 results obtained. Of course there was a whole world of 

 wonders outside these fields of inquiry. 



The view of the shadow of the moon from the summit 

 of Pike' s Peak cleaving its way along the lower air has 

 been described to me as one of the most striking pheno- 

 mena which it is possible to witness or imagine. The 

 shadow, the boundary of which was seen curved, was 

 preceded and followed by a spectrum. Where I was, 

 nearly 8,000 feet high, and therefore a little over mid- 

 height, there was no effect on the air, but after the close 

 of totality the shadow was observed passing over clouds 

 near the horizon. I may add, however, that the pheno- 

 mena at the beginning and end of totahty hardly existed 



for me, for I had to uncover and cover my photographic 

 plates at those times. 



It was not to be expected that in this country, where the 

 anxiety for news and views seems always to be at fever 

 heat, the astronomers would be allowed to quit their stations 

 without giving an idea of the tendency of their work, and 

 even its connection with the torrid temperature through 

 which we have had to make our dusty way, or in which 

 we have had to exist when locomotion had become 

 impossible. 



The utter disappearance of the large bright red corona 

 of former years in favour of a smaller and white one in 

 this year of minimum, struck everybody. Indeed it is a 

 remarkable thing that after all our past study of eclipses 

 this last one should have exhibited phenomena the least 

 anticipated. It isolates the matter that gives us the con- 

 tinuous spectrum from the other known gaseous con- 

 stituents. The present eclipse has accomplished, if 

 nothing else, the excellent result of intensifying cur 

 knowledge concerning the running down of the solar 

 energy. With the reduction of the number of spots or 

 prominences for the last four years the terrestrial mag- 

 netism has been less energetic than it has been for the 

 preceding forty years, while at both ends of this period 

 we have had famines in India and China. 



As the sun is the great prime mover of earth, and as 

 every cloud, every air current depends upon it, its present 

 quiet condition is worthy of the most minute study. The 

 absence of lines from the corona spectrum shows a great 

 reduction in the temperature of the sun, and such a 

 marked change in the sun should produce a correspond- 

 ing change on the earth, so that the associated terrestrial 

 phenomena should be carefully observed. Hence I 

 regard this eclipse as the most important that has been 

 observed for many years as it throws much needed light 

 on many points hitherto obscured in doubt. 



Prof. Morton, of the Stevens Institute of Technology, 

 remarked that the thing which impressed him most 

 was the very curious character of the result ; while on 

 former occasions there has been projected into the space 

 surrounding the sun a quantity of self-luminous gaseous 

 matter which has no fixed place there, we now see that 

 this was merely a temporary occupant which has, either 

 by diffusion into space or absorption into the body of the 

 sun, been removed. He also holds that the marked 

 changes in the sun' s condition would seem to call for cor- 

 responding marked changes in the condition of the earth. 

 The results, in fact, recall to his mind one of the early 

 theories of the maintenance of the sun's heat, which was 

 that it was maintained by the impact of meteoric matter 

 constantly falling in upon the sun from surrounding 

 space. The quantity of heat produced by such an infall 

 may be realised from the fact that a body so falling would 

 develop by impact as much heat as 5,000 times its weight 

 of carbon burnt in oxygen. Portions of the meteoric 

 matter in the shape of meteorites fall upon the earth, and 

 we thus know that most of them consist largely of iron, 

 containing considerable quantities of absorbed gases ; 

 others are of a metallic character and devoid of such 

 gases. If, now, we suppose that for a considerable period 

 the sun's fires were fed with hydrogen-charged faggots, 

 and then again that the main supply was of mineral 

 matter, w^e might have at first a far-reaching atmosphere 



