TRANSACTIONS OP SECTION A. 687 



nomers to the point in question in a paper read before the Royal Astronomical 

 Society in June, 1886, soon after which Mr. Cowper Ranyard, the late Mr. Whipple 

 of the Kew Observatory, and the late Father Perry of Stonyhurst, expressed them- 

 selves in close agreement on the whole with the author, the two former emphati- 

 cally so ; as also, quite lately, has Father Sidgreaves, Durector of the last-mentioned 

 observatory. 



Professor Sporer, also, of Munich, in a copious resumS of his labours in con- 

 nection with the solar spots (read at Geneva in August, 1885) denies that the spots 

 possess the character of funnels (tonnoirs) so commonly attributed to them. 



Not, however, that the statements of Wilson at the time when they were brought 

 forward remained unchallenged. For not only did the Rev. Francis WoUaston 

 (father of the great chemist) demur to them, but the great mathematician and 

 observer De la Lande (as recorded in the French Academy ' Memoirs ' for 1776) 

 admitted tliat whilst some spots behaved as Wilson states, yet that the rule by no 

 means always held good. Wilson's spot, moreover, of November, 1769, had so large 

 a size as a length and breadth of one minute of arc, and he states that the effects 

 of foreshortening even in a spot of such extensive dimensions was to cause the 

 central umbra to completely disappear when about 24" from the limb, whilst the 

 side of the penumbra nearest the limb still continued to be eminently conspicuous, 

 which would necessitate, of course, a very large amount of depth and of shelvino- 

 indeed ! _ The author of this paper, however, can only say that in repeated 

 observations he has never found any of this asserted foreshortening, nor con- 

 sequent apparent relative displacement of the umbra, when spots of the above- 

 mentioned size have been no more than 20", 15", or even 5" from the limb. The 

 author does not wish to affirm that no measure whatever of the foreshortening 

 ever occurs, but he emphatically affirms that where it does it is only in the ver'i/ 

 slightest degree, though it necessarily is somewhat more apparent in very small 

 spots. 



All these appearances can be readily exhibited on a globe of a foot or so in 

 diameter, in which depressions have been worked of various sizes and various 

 depths ; and from which it will at once be seen how very shallow must be the 

 spots which admit of the umbra remaining apparently central in the midst of the 

 penumbra, when so near the limb as has just been mentioned. 



Such, then, is the experience of the author of this paper, who also would wish 

 to state that in the present year he requested leave (and was most courteously 

 permitted) to corapare his hand-drawings of the sun for the last ten years em- 

 bracing two maximum and one minimum period of solar spot activitv — with the 

 photographic record at the Royal Observatory at Greenwich ; and when, as far 

 as could be perceived by means of a magnifying lens, his contention was found to 

 hold good in every instance in which the concurrent dates of observation admitted 

 of such a comparison, as was allowed by both Mr. Hollist and another junior mem- 

 ber of the assistants, who aided in the investigation. 



The appearance of a spot may, occasionally, seem to militate against the author's 

 views, and strongly to favour Wilson's, but, as Mr. Turner, chief assistant at 

 Greenwich, wrote him lately, ' the history of a spot needs studying.' And this is 

 very essential, because, on various occasions, a spot which when near the limb 

 seemed to favour Wilson was found not to do so when further from the limb, when 

 it was plainly evident that the umbra was not central. 



The results, finally, of the author's protracted observations and measurements 

 lead him to the conclusion that both the photospheric and also penumbral envelopes 

 of the sun are comparatively extremely shallow, and that the photosphere consists 

 of one layer only of the so-called ' rice-grain ' entities, lying in close contiguity to 

 the_ subjacent penumbra, and at most not more than the ^J^th part of the sun's 

 radius, or, say, about one thousand miles in thickness, and that the penumbral 

 stratiun is but little, if any, thicker ; otherwise the umbra could not remain jilainly 

 central within the penumbra (as it almost always does) when the latter is no more 

 than ten, or even five, seconds from the sun's limb. 



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