404 report— 1879. 



DEPARTMENT OF ANATOMY AND PHYSIOLOGY. 



Chairman op the Department.— P. H. Pye-Smith, B.A., M.D. 

 Vice-President of the Section. 



[For Dr. Pye Smith's Address see p. 406.] 



TRURSBA Y, A UG UST 21. 



The Department did not meet. 



Flill) A Y, A UG UST 22. 



The following Papers were read : — 



1. Observations on the Automatic Mechanism of the Batrachian Heart. 

 By Professor J. Burdon Sanderson, M.D., F.B.8. 



2. The Influence of Domestication on Brain-growth. 

 By W. F. Crtchton Browne. 



3. On a Daw of Retinal Activity. 

 By Professor Silvanus P. Thompson, B.A., D.Sc, fyc. 



A memoir was read by the author in 1877 before the Physical Section of the 

 Association ' On some new Optical Illusions,' some of which did not appear to accord 

 with any explanation hitherto offered. The illusions in question are those of the 

 subjective motion observed in apparent existence after the eye has for some time 

 been fixed upon a moving object, and which are executed, apparently in an opposite 

 direction. The most striking of these illusions are those produced by slight move- 

 ments given to certain patterns of lines and circles drawn in black upon a white 

 ground, and described in the author's memoir. The oldest illusions of apparent 

 motion are those recorded by R. Addams and by Brewster. While pointing out 

 that persistence of the retinal images failed to account for the production of these 

 illusions, the author abstained from advancing any completed theory until experi- 

 mental evidence was more complete. 



Quite recently Dr. Javal, Director of the Ophthalmological Laboratory of the 

 Sorbonne, has advanced an explanation of a different nature. He refers the pro- 

 duction of the subjective sensation of motion to small muscular movements uncon- 



