125 



rections, and exerting an important influence on all the phenomena of 

 terrestrial magnetism, both such as are general, and also such as 

 appear to be local anomalies. The later researches of the author 

 have satisfied him that the directions of these currents are probably 

 much influenced by the geological structure of the globe ; which 

 would in most cases tend to give them more or less obliquity to the 

 parallels of latitude. The author ascribes the diurnal changes in the 

 direction and intensity of terrestrial magnetism to the successive 

 action of the sun on the different portions of the surface of the globe. 

 With reference to the causes that have determined the juxtaposition 

 and arrangement of rocks in the interior of the earth, the author ex- 

 amines their comparative expansibility by heat. Granite, porphy- 

 ritic feldspar, and clay-slate expanded from one-50th to one-7/th by 

 a red heat ; while the expansion of serpentine, by the same heat, 

 could not be rendered sensible. He concludes by calling in ques- 

 tion the theory which ascribes the spheroidal form of the earth to its 

 having been once a mass of plastic matter in igneous fusion or in 

 aqueous solution. 



May 17, 1832. 



The Rev. WILLIAM BUCKLAND, D.D., Vice President, 

 in the Chair. 



The reading of a Paper, entitled, "On Harriot's Astronomical 

 Observations contained in his unpublished Manuscripts belonging to 

 the Earl of Egremont," by Stephen Peter Rigaud, Esq. M.A. F.R.S. 

 Savilian Professor of Astronomy in the University of Oxford, — was 

 commenced. 



May 24, 1832. 



DAVIES GILBERT, Esq. D.C.L., Vice President, in the Chair. 



The reading of Professor Rigaud's Paper was resumed and con- 

 cluded. 



In the Memoirs of the Royal and Imperial Academy of Brussels, 

 for the year 1788, the Baron de Zach published a paper on the pla- 

 net Uranus, in a note to which he states that, in the summer of 1784, 

 he found in the library of Lord Egremont at Petworth, some old ma- 

 nuscripts of the celebrated Thomas Harriot, which he alleges afforded 

 proofs that he had observed the solar spots, and the satellites of Ju- 

 piter before Galileo. In the Berlin Ephemeris for 1788, Baron 

 Zach gave a full account of his alleged discovery, drawn up from 

 Harriot's papers \ an English translation of which was circulated in 

 this country, and has been perpetuated by its being inserted in Dr. 

 Hutton's Mathematical Dictionary. The author, having been en- 

 trusted by Lord Egremont with Harriot's original papers, has ex- 

 amined them with every attention he could apply to the subject, and 

 gives in the present memoir the result of his inquiry. 



The observations of Harriot on the spots on the sun, fill seventy- 

 four half-sheets of foolscap, the first being dated December 8, 1610. 



k 2 



