46 Prof. Phillips Physical Aspect of the Sun. [Jan. 26, 



Mr. Main's observations with the splendid Oxford Heliometer give as the 

 most probable result, the large fraction of g^g for 1862. This excellent 

 astronomer has continued his observations during the late opposition. My 

 own attempts to obtain the ellipticity with the micrometer eyepiece reading 

 to 0"'2 of arc failed to give satisfactory measures. The ellipticity, indeed, 

 seemed to be small, and was merely observable, not really measurable or 

 even to be approximately estimated by the help of this apparatus. 



IV. " Notices of the Physical Aspect of the Sun." By JOHN PHIL- 

 LIPS, M.A., LL.D., F.R.S., F.G.S., Professor of Geology in the 

 University of Oxford. Received January 13, 1865. 

 PART I. 



Frequently, during many years, the peculiarities of the physical aspect 

 of the sun have arrested my attention, and induced me often to sketch 

 and sometimes to measure ; but until Mr. Cooke furnished me with the 

 accurate and convenient equatorial which I now employ, there seemed 

 little hope of my being able to draw correctly or observe systematically. 

 During some late occasions I have endeavoured to obtain trustworthy 

 representations not only of some of the darker tracts, denominated " spots," 

 and the brighter parts which are near them, called " faculee," but also of 

 the general uneven groundwork of the sun's disk. 



In tracing the path of a " spot " across the disk of the sun, I employ a 

 Kelluer (positive) eyepiece of about 50 linear, on which are engraved 

 five transit-lines, at intervals of about T 1 i V of the sun's diameter, and there- 

 fore, near the centre of the disk, about equal to 10. Having, with this 

 eyepiece applied to the diagonal sun-glass, and the clock movement, de- 

 termined the position of the spots, I replace the Kellner by ordinary 

 (negative) eyepieces, whose powers range from 75 to 300, the latter 

 being seldom beneficial except for objects near the limb, and in very fa- 

 vourable weather which, in my experience, means a partially clouded 

 sky, westerly winds, and morning hours by preference. Some of the 

 clearest views which I have experienced were had in the intervals of 

 storms and snow-clouds the slowly drifting snow-flakes of those clouds 

 being visible as dark spots in the field of view, when the eyepiece was 

 adjusted to their very moderate distance *. 



I present a diagramf showing the appearance of the sun's disk on the 

 29th of March, 1864, and other sketches of the bright and shady parts 

 of the surface. From the variations in the appearance of the spots, 

 faculae, and ground surface, many suggestions arise ; but I limit myself on 

 this occasion to some inferences which appear justified by the observations 

 of the least variable of them. So great is the diversity in the short 



* I have occasionally employed the telescope to measure the distances and heights of 

 clouds, employing for the purpose a well-known formula. 



t Of the drawings accompanying this paper, which are referred to by numbers, Nos. 

 3, 4, and 5 are given in Plate III. ; the rest are preserved in the Archives. 



