19 



excitement of the fibres. It is supposed, however, that even a 

 perfectly homogeneous colour, red for example, excites, though 

 feebly, the fibres conveying green and violet. Consequently it is 

 believed that a perfectly pure colour has never been seen. 



"After images" due to the fatigue of nerve fibres recently 

 excited, were shown by aid of the magnesium light. 



Colour blindness is supposed to be due to the paralysis of one 

 set of the fibres just described, generally of the red, with the result 

 that there is inability to distinguish between scarlet and green, and 

 rose tint and blue. About twenty men, but only one woman, in a 

 thousand, are colour blind. Alcohol, tobacco, and santonate of 

 soda can temporarily cause colour blindness. 



The lecturer, finally, endeavoured to explain why, since our 

 vision is limited to the formation of a very small inverted image on 

 a plane surface, we see objects as if erect, and solid ; and how we 

 are enabled to estimate their distance and position. 



SATURDAY, JUNE 18th. 



The members and their friends spent the afternoon at Kew 

 Gardens, which they visited under the guidance of W. T. 

 Thiselton Dyer, Esq., F.E.S. At 6 o'clock a cold collation was 

 provided at the "Coach and Horses Hotel," Kew Green. 



SATURDAY, OCTOBER 22nd. 



The members and their friends visited the Zoological Gardens, 

 Regent's Park. The party assembled at the north entrance of the 

 Gardens, at 2.30 p.m. Here they were met by J. Jenner "Weik, 

 Esq., F.L.S., F.Z.S., who conducted them round a portion of the 

 grounds, and gave a most instructive account of the more important 

 and interesting of the animals. The party dined in the evening at 

 the Caf6 Restaurant Royal, Regent Street. 



