546 Mr. A. W. Rlicker and Prof. T. E. Thorpe. [Apr. 11, 



Jacob! (A.) Contributions to the Anatomy and Pathology of the 

 Thymus Gland. 8vo. Philadelphia 1888. The Author.' 



Lewis (T. R.) Effigy Mounds in Northern Illinois. 8vo. St. Paul, 

 Minn. 1888. The Author. 



Sharp (W.), F.R.S. Therapeutics ought to become a Science. 

 Essay 52. 8vo. London 1888; Therapeutics can become a 

 Science.' Essay 54. 8vo. London 1889. The Author. 



Siemens (C. W.) The Scientific Works of C. William Siemens, 

 F.R.S. Edited by E. F. Bamber, C.E. 3 vols. 8vo. London 

 1889. Executors of the late Sir William Siemens. 



Wolf (R.) Astronomische Mittheilungen. December 1888. 8vo. 

 [Zurich']. Dr. Wolf. 



Photograph of the portrait of John Evelyn, F.R.S., in the possession 

 of the Royal Society. Dr. Frankland, F.R.S. 



April 11, 1889. 

 Professor G. G. STOKES, D.C.L., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The Bakerian Lecture was delivered as follows : 



BAKERIAN LECTURE. "A Magnetic Survey of the British Isles 

 for the Epoch January 1, 1886." By A. W. RiJCKER, M.A., 

 F.R.S., and T. E. THORPE, B.So., Ph.D., F.R.iS. Received 

 (in abstract) April 11, 1889. 



(Abstract.) 



Two magnetic surveys of the British Isles have been made previous 

 to that of which an account is given in this paper. The necessary 

 observations were taken between the years 1834-38 and 1857-62, and 

 the results were reduced to the epoch 1842*5 by Sir E. Sabine (' Phil. 

 Trans.,' 1870, p. 265). The stations in these were very irregularly 

 distributed over the area under investigation, the declination was 

 determined at but few places, and the force in the earlier survey was 

 only determined relatively to London. 



In the five years 1884-88, both inclusive, the authors have made an 



