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XXXVI. — On Sun-Spots and their Connection with Planetary Configurations. By 



Balfour Stewart, Esq., M.A., F.R.S. 



(Read 18th April 1864.) 



In pursuance of an idea which occurred independently to Professor Tait and 

 myself, a careful examination has been made of the solar autographs, taken at 

 Kew and Cranford, under the superintendence of Mr Warren De la Rue. This 

 was done with the view of detecting, if possible, some reference to planetary con- 

 figurations in the behaviour of sun-spots, and in this undertaking, much aid was 

 derived from a remark once made by Mr Beckley of Kew, when taking pictures of 

 the sun, to the effect that, for a considerable period of time, he did not observe any 

 spots in the act of hreahing out on the visible disc of our luminary. A few words 

 may not be amiss regarding the nature of the scrutiny to which the solar pictures 

 were subjected, and also the value of this as a test of planetary action. In the 

 first place, let us bear in mind, that by the rotation of our luminary, the different 

 portions of his surface are successively presented to each planet in turn. Now, if 

 the bodies of our system have any appreciable influence of this kind upon the 

 sun, it is natural to expect that this should differ for any given portion of his 

 surface, according as this portion is presented to the influencing body, or with- 

 drawn by rotation, so that the sun's diameter is interposed between it and the 

 planet. We should therefore expect to find that, for a given date, the spots 

 should all begin to break out into visibility at or about the same ecliptical longi- 

 tude. Similarly with regard to their healing up ; and, generally, all spots on 

 the sun's disc at a given date should behave in the same manner as they pass 

 a given ecliptical longitude. 



It is needless to conceal the great difficulty, if not impossibility, of a complete 

 and final examination of sun-pictures after this method ; but, on the other hand, 

 very little consideration is required to show us its great value as a test of the/«c^ 

 of planetary action. For if it once be proved (which may easily be done by means 

 of sun pictures), that all the spots on the sun's disc at a given date behave in the 

 same manner, as they pass a given ecliptical longitude, me are then compelled to 

 resort to planetary action as the only conceivable explanation of such a. phenomenon. 

 In the sun pictures taken by the Kew Heliograph, a vertical line denotes a north 

 and south line through the sun's disc — that is to say, such a line denotes a section 

 of the sun's surface, by a plane passing through the earth's axis ; and therefore 

 perpendicular to the plane of the equator. When this plane passes also through 

 the pole of the ecliptic, which it will do twice a year, the vertical diameter of the 

 picture will denote a line of ecliptical longitude; but in the following very 



VOL. XXIII. PART III, 6 T 



