August 2 2, 1878] 



NATURE 



431 



netic storms and aurorae, heavy rainfall, and, let me add, 

 no famines to speak of. Associated with these we had a 

 large corona. This year there are no spots, the promi- 

 nences are rare, the magnets were never so quiet, there 

 are no aurorae, and we are passing through a famine 

 period. Associated with these we had a small corona. 

 Hence it is that the astronomers agree that this year 

 another connecting link has been added to the chain 

 which binds together the solar changes. 



On another point mentioned in my telegram the evi- 

 dence is overwhelming. Since the use of the spectroscope 

 in this branch of inquiry the spectrum of the corona has 

 been observed to be a mixed one — that is, bright lines as 

 well as a continuous spectrum have been traced in it. In 

 1869 and 1 87 1 these lines were very bright to the eye — 

 much brighter than the continuous spectrum, while in 

 1875, when the spectrum was photographed for the first 

 time, the record showed the lines to be much brighter 

 than the continous spectrum. Now, as it generally 

 happens that when in our laboratories we study gaseous 

 spectra there is a faint continuous spectrum accompanying 

 the lines, it was thought that the spectrum of the solar 

 corona might have a gaseous origin exclusively. This 

 year's observations have quite dispelled this idea, for the 

 two elements of the corona spectrum, to which attention 

 has been drawn, instead of varying directly, vary inversely. 

 The continuous spectrum has been seen and photographed 

 by itself, without any bright lines. Now for the interpre- 

 tation of this hieroglyphic language. The gases which 

 were high up in the sun's atmosphere at the last epoch of 

 maximum sun-spots (1871), have almost entirely retreated 

 to a lower level ; as these gases are to a large extent 

 carriers of heat from the interior to the exterior of 

 the sun, the exterior is cooler in their absence, and 

 indeed cool enough to allow it to hold in suspension 

 a larger percentage of solid and liquid particles to which 

 the continuous spectrum is due. A natural suggestion 

 touching these particles is that they consist of meteoritic 

 matter, and all the phenomena to which attention has 

 been drawn can be explained by supposing that these 

 meteorites surround the sun, and that at the minimum 

 sun-spot period they can exist lower down in consequence 

 of the reduced temperature of the sun's atmosphere at 

 that time. If this suggestion, which is the one in favour 

 out here, be endorsed we have a partial cause of reduced 

 solar radiation at that time. I cannot quit this part of 

 the subject without referring to the wealth of astronomi- 

 cal resources which have been brought to bear upon it. 

 Paper astronomers have been now for a long time, I 

 doubt not, very lucratively employed in proving that it 

 was impossible to do exactly what has been done. Dr. 

 Draper, who ranks deservedly high among solar ob- 

 servers, bears off the palm by the strength of his attack. 

 He used a camera of six inches aperture and of only 

 twenty-one inches focal length, and, by means of a 

 Rutherfurd grating two inches square, obtained a photo- 

 graph of the corona and two of its spectra with the same 

 instrument. The plates were exposed during the whole 

 of totality, and it is encouraging for future work to know 

 that much less exposure would have sufficed to secure 

 the precious records, although the continuous spectrum 

 recorded is the most difficult to obtain. Prof. Harkness 

 used an instrument of nearly equal power, though of 

 slightly different arrangement. The smallest instruments 

 employed — ordinary portrait cameras with a grating in 

 front — also gave the same result, though, of course, on a 

 much smaller scale. 



Next comes the endorsement of the fact that the 

 coronal light is due partly to solar light — that all the 

 light it sends to us is not its own. Prof. Barker, with 

 Dr. Draper's party at Rawlings, though he saw no bright 

 lines, saw dark ones in abundance ; and Prof. Morton 

 got distinct traces of radial polarisation, thereby endorsing 

 the result obtained in 1871. The object of these observa- 



tions by the polariscope is to determine^ whether and in 

 what plane hght is reflected; and for' the light to be 

 reflected to us by particles in the sun's atmosphere we 

 must imagine our eye, the centre of the sun, and the 

 particle to lie in one plane. If, further, we imagine an 

 infinite series of particles surrounding the sun, we shall 

 have an infinite series of these planes, and each radius of 

 the sun will lie in one of them. I have been particular in 

 stating this, because Prof. Hastings, a great authority in 

 optical matters, declares that the reflection takes place at 

 right angles to these radial planes ; in other words, he 

 declares that the polarisation is tangential and not radial. 

 As has been well remarked, this result is easily explained 

 by supposing ice crystals to be present in the sun' s atmo- 

 sphere, and no other solution lies on the surface. I 

 believe no one is more astonished than Prof Hastings at 

 his observation ; and here again we see the necessity of 

 relaxing no efforts and letting slip no opportunity of 

 garnering the observations with which eclipses alone 

 supply us. 



Finally, as to the construction of the corona. Number- 

 less records of this, both visual and photographic, have 

 been secured, and as usual, though there is almost perfect 

 agreement as to the structure of the lower portion, the 

 rays and streamers have been very variously observed. 

 The upper and lower portions of the sun were graced by 

 the most exquisite tracery, bending over right and left 

 like plumes of ostrich feathers, the intervals between 

 them being of a delicate blue. Near the solar equator 

 the structure was not so obvious. Still, it was there, for 

 Prof. Bass saw it come out and pulsate after he had fixed 

 his eye on one portion for two minutes. The structure was 

 distinctly less filamentous than in 1871. With regard to 

 the streamers there appears to have been two sets— one 

 along the ecliptic, giving rise to the appearance of a wind 

 vane seen by one set of observers; another, at right 

 angles to this, seen by another set. Neither of these 

 systems of streamers was visible in a telescope, though 

 the base of the ecliptical ones appears on the photo- 

 graphs. On this point the greatest weight must be given 

 to the observers on Pike's Peak, 14,147 feet high. Most 

 fortunately the weather there as elsewhere was superb, 

 and the corona was seen as it was never seen before. 

 The clearness of the sky in this region when the weather 

 is good is simply wonderful. The Milky Way seems to 

 have deep holes in it, and the individual stars shine out. 

 Even at Rawlings Prof. Watson could see the satel- 

 lites of Jupiter with the naked eye. At Pike's Peak 

 General Myer saw the corona for fully five minutes after 

 totality was over, while in India, in 1871, the much 

 brighter corona was seen at sea-level for only three 

 minutes after the eclipse was over, f Prof Cleveland 

 Abbe, who, as already stated, observed below the Peak, 

 saw the ecliptic streamers extending to a distance of 

 twelve solar diameters, while he saw nothing of the north 

 and south ones, pretty conclusive evidence in favour of 

 their subjectivity, and from their appearance he has little 

 doubt of their being meteor streams. Prof. Newcomb 

 saw the ecliptic streamers almost equally well at Separa- 

 tion by the help of a novel contrivance. He had a disc 

 erected on a high pole at some distance from his tele- 

 scope so that he could momentarily cover the dark moon 

 and corona and observe the external phenomena with the 

 naked eye. In this way he saw the streamers extending 

 nearly as far as Prof. Abbe did. Still he explains them 

 differently. He considers that they indicate the true 

 zodiacal light. No doubt there are difficulties surround- 

 ing both suggestions, and here again we see the need for 

 future thought and work. The regions in which the 

 various parties were located enabled many of the con- 

 nected phenomena to be observed as they had never been 

 before. From Pike's Peak, with its horizon of 150 miles 

 on all sides, the shadow of the moon sweeping rapidly 

 through the air was a very tangible thing and seemed to 



