Hoy al Society. 131 



From the discovery which was made of the non-coincidence of 

 the locality of the maximum magnetic intensity, within the Arctic 

 circle, with that in which the magnetic direction is vertical, it fol- 

 lowed that the generally prevailing opinions respecting the distri- 

 bution of magnetic force at the surface of the earth were erroneous, 

 and that even the broad outline of the picture of terrestrial mag- 

 netism required to be recast. For the purpose of obtaining suffi- 

 ciently copious and accurate materials, by means of which so de- 

 sirable an object could be accomplished, the British Association for 

 the Advancement of Science requested, in the year 1835, a report to 

 be prepared, in which the state of our knowledge, collected from a 

 great variety of sources, with regard to the variations of the mag- 

 netic force at different parts of the earth's surface, should be re- 

 viewed, and properly discussed, and suggestions offered as to the 

 best means of extending the inquiry. In the report so obtained, it 

 was recommended that magnetic surveys of that portion of the 

 North American Continent, which is comprised within certain iso- 

 dynamic lines, should be procured. The present paper contains the 

 results of an expedition towards the accomplishment of this object, 

 recommended by the President and Council of the Royal Society 

 to be undertaken under the auspices and with the assistance of the 

 Hudson's Bay Company. Lieutenant Lefroy, of the Royal Artil- 

 lery, who had received an appointment to the Toronto Observatory, 

 with a special view to this survey, was entrusted with the conduct 

 of an expedition in conformity with that recommendation. 



The author gives a circumstantial narrative of the expedition, 

 together with minute details of the instruments employed, and the 

 methods of observation adopted; and extensive tables of the ob- 

 servations themselves, both as regards intensity and inclination, at 

 the different stations where they were made, occupying altogether 

 about 120 folio pages of manuscript. 



It results from the calculations founded on the data furnished by 

 these observations, that the geographical position of the point of 

 maximum intensity, where its amount is 1*88, is 52° 19'*3 north 

 latitude, and 268° 01* longitude. The angle which the major axis 

 of the ellipse makes with the parallel of geographical latitude is 

 57° 49'*5 ; and the values of the semi-axes of the ellipse of 1*875 

 are 290 and 110 geographical miles respectively. 



May 28. — " An Account of the desquamation and change of 

 colour in a Negro of Upper Guinea, West Africa." By the Rev. 

 Thomas S. Savage, M.D., Corr. Member of the Boston Natural Hi- 

 story Society, &c. Communicated by Richard Owen, Esq., F.R.S. 



The subject of this narrative, named Tahtoo Duari, is a member 

 of the Grebo tribe, the aboriginal inhabitants of Cape Palmas and 

 its vicinity. His parents were members of the same tribe and 

 natives of the same region. The father was of a decidedly black 

 complexion, while the mother was what is termed yellow, the two 

 extremes observable in the tribe, and between which there is found 

 every variety of shade. In March 1844, when about twenty-five 

 years of age, Tahtoo was attacked with a quotidian ague, having 



K2 



