110 BEITISH ASSOCIATION TOE THE 



She has been built for the Husum and Hoyer Steam Packet Company, composed 

 of Danish and English proprietors, to ply between those places and the islands, in 

 connection with the Royal Danish Railway, which connects the North Sea with 

 the Baltic. This railway, the result of the skill and enterprise of Sir S. M. Peto 

 and his friends, is now in full operation, and has not only opened a short and 

 expeditious route to the Baltic, but has placed at the disposal of our markets an 

 almost inexhaustible supply of cattle and grain. To the port of Tonuing, on the 

 Eider, the North Sea terminus of this railway, a place but little known a few 

 years since, two large steamers, belonging to the North of Europe Steam Navi- 

 gation Company, ply weekly from London and Hull ; whilst on the opposite 

 side, at Flensburg, on the Baltic, a fleet of smaller steamers, belonging to the 

 same company, maintain the communication with Copenhagen, Husum, Aarhuus, 

 Stettin, Dantzic, Konisberg, and St. Petersburg. 



TH E BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE 



(Concluded.) 



Cheltenham, 6th August, 1856. 



"unequal sensibility of the foramen centrale to light of different colours," 

 by mr. j. c. maxwell. 



When observing the spectrum formed by looking at a long vertical slit through 

 a simple prism, I noticed an elongated dark spot running up and down in the blue, 

 and following the motion of the eye as it moved up and down the spectrum, but 

 refusing to pass out of the blue into the other colours. It was plain that the spot 

 belonged both to the eye and to the blue part of the spectrum. The result to which 

 I have come is, that the appearauce is due to the yellow spot on the retina, com- 

 monly called the Foramen Centrale of Soemmering. The most convenient method 

 of observing the spot is by presenting to the eye, in not too rapid succession, blue 

 and yellow glasses, or, still better, allowing blue and yellow papers to revolve 

 slowly before the eye. In this way the spot is seen to fade away in time, and to 

 be renewed every time the yellow comes in to relieve the effect of the blue. By 

 using a Nicol's prism along with this apparatus the brushes of Haidinger are well 

 seen in connexion with the spot, and the fact of the brushes being the spot ana- 

 lyzed by polarized light becomes evident. If we look steadily at an object behind 

 a series of bright bars which move in front of it, we shall see a curious bending 

 of the bars as they come up to the place of the yellow spot. The part which 

 comes over the spot seems to start in advance of the rest of the bar, and this 

 would seem to indicate a greater rapidity of sensation at the yellow spot than in 

 the surrounding retina. But I find the experiment difficult, and I hope for better 

 results from more accurate observers. 



" ON AN INSTRUMENT TO. ILLUSTRATE POINSOT's THEORY OF ROTATION," BY MR. J. C. 

 MAXWELL. 



In studying the rotation of a solid body according to Poinsot's method, we have 

 to consider the successive positions of the instantaneous axis of rotation with 

 reference both to directions fixed in space and axes assumed in the moving body. 

 The paths traced out by the pole of this axis on the invariable plane and on the 

 central ellipsoid form interesting subjects ofmathematical investigation. But, when 



