306 Proceedings of Philosophical Societies. [April, 



teen years past, whenever his stomach is considerably deranged : 

 another friend was attacked by pain at the left temple, and at 

 the back of the left eye, which was succeeded by this sort of 

 blindness on the right side of each eye ; he can see to write, — 

 see the paper he is writing upon, and the pen he writes with, — 

 but not the hand that guides the pen. The affection in this 

 case, Dr. W. fears, is a permanent one ; the pain first expe- 

 rienced seems to have arisen from some effusion causing a 

 degree of pressure on the brain, and the blindness from the 

 continuance of this pressure on the left thalamus nervorum 

 opticorum. 



Now all these cases seem referable to the partial insensibility 

 of each retina, and they indicate that the left side of the retina 

 in each eye is supplied with nerves from the same thalamus, and 

 the right from the opposite thalamus; so that the nerves supplying 

 the former alone decussate, and not those of the right side ; an 

 arrangement which Dr. Wollaston calls the semi-decussation of 

 the optic nerves. 



Dr. Wollaston proceeded to illustrate this statement of the 

 distribution of the optic nerves, from that observed in those of 

 fishes : in the sturgeon the eyes are diametrically opposite each 

 other, each on one side of the head, the left eye being entirely 

 supplied with nerves from the left thalamus of the brain, and the 

 right eye entirely from the right thalamus. The blindness above 

 described, Dr. W. remarked, does not appear to be rare, but is 

 seldom particularly noticed, like many other things, because it 

 is not understood. 



This very interesting paper concluded with a short section in 

 which Dr. Wollaston applies the sympathy of structure in the 

 eyes, indicated by the effects just noticed, to the explanation of 

 the long agitated question respecting the cause of single vision 

 with two eyes. Every point in each eye is supplied with a pair 

 of filaments from the same nerve, and the two eyes thus sympa- 

 thize with each other in every point : hence arises single vision ; 

 and hence also the reason why infants direct both eyes in a 

 corresponding direction, instead of squinting. 



Feb. 26. — A Catalogue was presented from the Rev. Fearon 

 Fallows, FRS. Astronomer at the Cape of Good Hope, of nearly 

 all the principal Fixed Stars between the zenith of Cape Town, 

 Cape of Good Hope, and the South Pole. 



A paper was read, " On the various Degrees of Intensity of 

 the local Magnetic Attraction in different Parts of Ships ; by 

 George Harvey, MAS. Communicated by John Barrow, Esq. 

 FRS. Secretary to the Admiralty." 



March 4.— William Wavell, MD. and Capt. Philip Parker 

 King, RN. were admitted Fellows of the Society ; the Lord 

 Bishop of Limerick, and the Rev. Dr. E. Maltby, Prebendary of 

 Lincoln, being unable to attend for admission, requested to have 

 their names inserted in the printed lists of the Society, which 

 was granted accordingly. 



