268 Proceedings of the British Association, 



lines under discussion were concerned, he had no doubt upon his 

 own mind of the completeness of the explanation which he had 

 given. — Prof. Powell had repeated Sir D. Brewster's experiments, 

 and had found the facts to be rigorously as stated by him. He 

 had also read with much care both papers of the Astronomer 

 Royal on the subject, and expressed his conviction that the last 

 one contained a complete explanation of the phenomena at that time 

 described. It was obvious that cases might occur where the pheno- 

 mena were complicated, and where some parts would depend for ex- 

 planation on one principle, others on another, though observed to- 

 gether ; but he did not think it fair, even supposing the phenomena 

 remained still unexplained, to say that therefore they were incapable 

 of being explained by the Undulatory Theory. 



Sir D. Brewster next submitted a notice of Two New Properties 

 of the Retina. — One of these properties related to the inferior sen- 

 sibility of the retina at that part of it which corresponded to the Fora- 

 men centrale of Soemmering, and which opened itself only when the 

 eyes were directed to a faintly illuminated surface. The other pro- 

 perty of the retina appeared after the observer's eye had been im- 

 pressed with the luminous stripes seen by looking out of a railway 

 carriage in rapid motion, at the stones, or rather white bodies lying 

 near the rails. When the eye is quickly shut under this impression, 

 a motion is perceived in a direction transverse to the real impression 

 on the retina ; and there is the appearance of a complementary lens 

 in the same transverse direction. 



'On the Aberration of Light,' by the Rev. Prof. Challis. — The 

 phenomenon of aberration was explained on the undulatory theory of 

 light, by assuming the direction of vision to be always co-incident with 

 the direction of propagation of the waves. A star, according to this 

 supposition, is seen in its proper direction, while an object which 

 moves with the spectator is seen in a direction which, with respect 

 to the earth's motion, is behind its true place. Astronomical obser- 

 vation does not determine whether aberration affects the apparent 

 position of the wire of the telescope, or of the star. Assuming the 

 position of the star to be changed, it follows from this view, that the 

 star must be considered to be in advance of its true place as regards 

 the direction of the earth's motion, and this result is in accordance with 



