Royal Institution, 57 



spectrum-observation. Like Galileo searching the heavens with his 

 newly-made telescope, the Professor becomes for the time the wisest 

 of men, and reveals the composition of the sun with a kind of dig- 

 nity worthy of the occasion. 



Before closing his memoir, Kirchhoff enters into a very interesting 

 discussion as to the constitution of the sun's surface and atmosphere. 

 After totally refuting the old physical hypothesis of Sir William 

 Herschel, Arago, and others, he concludes that the sun's spots, instead 

 of being cavities in a photosphere, are black clouds elevated above the 

 luminous surface of the sun's body ; he shows also that the perspect- 

 ive phenomena which led Alexander Wilson to consider the spots as 

 cavities, are at least partially explicable on this cloud theory. After 

 much reflection, however, we are inclined to think that this new pro- 

 position is not only inconsistent with the general testimony and 

 belief of those who have most minutely examined the sun's surface, 

 but is decisively contradicted by the following observation of Sir 

 William Herschel* : — 



"Oct. 13, 1794. The spot in the sun I observed yesterday is 

 drawn so near the margin, that the elevated side of the following 

 part of it hides all the black ground, and still leaves the cavity visible, 

 so that the depression of the black spots and the elevation of the 

 faculse are equally evident." 



We might point also to the original drawing by Wilson of the 

 great spot of 1769 f as partially exhibiting the same appearance. 

 But the subject is one eminently debatable and worthy of debate : 

 no one at all interested in the subject can omit studying Professor 

 Kirchhoff's able arguments ; but every reader is as yet, we think, 

 free to draw his own conclusions. 



XI. Proceedings of Learned Societies. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



June 6, 1862.— The Duke of Northumberland, K.G., F.R.S., 



President, in the Chair. 



ON Force." By John Tyndall, Esq., F.R.S., Professor of 

 Natural Philosophy, Royal Institution. 

 The existence of the International Exhibition suggested to our 

 Honorary Secretary the idea of devoting the Friday evenings after 

 Easter of the present year to discourses on the various agencies on 

 which the material strength of England is based. He wished to 

 make iron, coal, cotton, and kindred matters the subjects of these 

 discourses, — opening the series by a discourse on the Great Exhibi- 

 tion itself. And he wished me to finish the series by a discourse on 

 " Force " in general. For some months I thought over the subject 

 at intervals, and had devised a plan of dealing with it ; but three 

 weeks ago I was induced to swerve from this plan, for reasons which 

 shall be made known towards the conclusion of the discourse. 



* Phil. Trans. 1795, p. 58. f Ibid. 1774, p. 8. 



