262 Dr. S. Bidwell. On Negative After-images, and 



May 23, 1901. 



Sir WILLIAM HUGGINS, K.C.B., D.C.L., President, in the Chair. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



Professor James Gordon MacGregor was admitted into the Society. 



The following Papers were read : — 



I. " On the Presence of a Glycolytic Enzyme in Muscle." By Sir 

 Lauder Brunton, F.R.S., and Herbert Rhodes. 



II. " On Negative After-images and their Relation to certain other 

 Visual Phenomena." By S. Bidwell, F.R.S. 



III. "The Solar Activity 1833-1900." By Dr. W. J. S. Lockyer. 



Communicated by Sir Norman Lockyer, K.C.B., F.R.S. 



IV. "A Comparative Crystallographical Study of the Double Selenates 



of the Series R 2 M(Se0 4 ) 2 ,6H 2 0. — Salts in which M is Magne- 

 sium." By A. E. Tutton, F.R.S. 



V. " On the Intimate Structure of Crystals. Part V.— Cubic Crystals 

 with Octahedral Cleavage." By Professor W. J. Sollas, F.R.S. 



VI. "Preliminary Statement on the Prothalli of Ophioglosmm pen- 

 dulum, L., Helminthodachys zeylcuiica, Hook., and Psilotum sp" 

 By Dr. W. H. Lang. Communicated by Professor Bower, 

 F.R.S. 



The Society adjourned over the Whitsuntide Recess to Thursday, 

 June 6. 



" On Negative After-images, and their Relation to certain other 

 Visual Phenomena," By Shelford Bidwell, M.A., Sc.D., 

 F.R.S. Received May 1 — Read May 23, 1901. 



I. Preliminary. 



In a former communication I described a curious phenomenon due 

 to the formation of negative after-images following brief retinal 

 excitation after a period of darkness.* The effect is conveniently 

 demonstrated by the aid of a disc, partly black and partly white, 



* < Roy. Soc. Proc.,' 1897, vol. 61, p. 268. 



