610 



to some extent, when we fix the eye's axes in a given direction ; and 

 severely, whenever we wilfully strain our vision thus astonishing us 

 by the flitting away of objects from our sight, burying some in quasi- 

 lucid clouds, as if they had overspread one another, and as the 

 origin of the phenomenon was undetected, occasioning many sur- 

 mises upon the inherent qualities of the special nervous structure in 

 order to account for them. An observation upon the inverted image 

 of a candle formed at the posterior face of the crystalline lens is 

 mentioned, which indicates other muscular action besides that which 

 rotates the eyeball, when the eye is vehemently strained, as if the 

 lens becomes flattened. The phenomena which inform us of a dif- 

 ferential structure in the retinal surface, with respect to the punctum 

 caecum, foramen centrale, and the elementary rods and cones, which 

 II. Muller believes to constitute the sentient layer, are adduced ; as well 

 as the conclusions to which we are led, after eliminating the various 

 phenomena studied, as regards the ultimate structure of the sentient 

 surface. 



VIII. " On Hourly Observations of the Magnetic Declination, 

 made by Captain Rochfort Maguire, R.N., and the Officers 

 of H. M. Ship ' Plover/ in 1852, 1853 and 1854, at Point 

 Barrow, on the shores of the Polar Sea." By Major-General 

 EDWARD SABINE, R.A., D.C.L., Treas. and Vice- President 

 R.S. Received August 14, 1857. 



(Abstract.) 



Point Barrow is the most northern cape of that part of the Ame- 

 rican continent which lies between Behring Strait and the Mackenzie 

 River. It was the station, from the summer of 1852 to the summer 

 of 1854, of H.M.S. 'Plover,' furnished with supplies of provisions, 

 &c. for Sir John Franklin's ships, or for their crews, had they suc- 

 ceeded in making their way through the land-locked and ice-encum- 

 bered channel by which they sought to effect a passage from the 

 Atlantic to the Pacific. In this most dreary, and apparently unin- 

 teresting abode, Captain Maguire and his officers happily found an 

 occupation in observing and recording, for seventeen months unre- 

 mittingly, the hourly variations of the magnetic declination and of the 



