1895.] 3Ir Griffiths, The Calibration of a Bridge Wire. 273 



affect the galvanometer readings even if the rate of fall of both 

 batteries is the same. 



I do not see, therefore, that the Von Helmholtz method, as 

 described by Giese, has any advantage over the ordinary Wheat- 

 stone's-Bridge method of Calibration, except in so far as it affords 

 an independent mode of investigation. 



My method was specially designed to eliminate the causes of 

 error above enumerated, and, although I now find that I cannot 

 lay claim to priority as far as the use of a double circuit is 

 concerned, the methods are in all other respects so essentially 

 different that I leave my communication unaltered in the hope 

 that it may be of use to others. 



Monday, 25 February, 1895. 



Mr K. T. Glazebrook, Treasurer, in the Chair. 



Mr C. J. Lay, Fellow of St Catharine's College, was elected a 

 Fellow of the Society. 



The following Communications were made to the Society : 



(1) On Binocular Colour-mixture. By W. H. R. Rivers, 

 M.D. Lond., St John's College. 



There has been much difference of opinion among workers 

 in physiological optics on the question of the occurrence of 

 binocular colour-mixture. Volkers, Dove, Regnault, Foucault, 

 Brlicke, Fechner, Ludwig, Panum, Hering, Aubert, Forster and 

 Chauveau are among those who have seen the appropriate 

 mixture-colour when a different colour-stimulus is presented 

 to each eye; but several observers of the greatest eminence, viz. 

 Wheatstone, Meyer, Volkmann, Meissner, Funke and Helmholtz 

 have been unable to satisfy themselves that binocular mixture 

 occurs. 



The object of the present paper is to bring forward the fact 

 that binocular colour-mixture may be observed in the after-image, 

 and to consider some possible causes of the different results which 

 different observers have obtained. 



I may mention first that there are two methods by which 

 I can most readily see, and show to others, binocular mixture, 

 viz. that described by Hering^, of which I show a modification 

 devised by Mr E. T. Dixon, and by means of Wheatstone's stereo- 

 scope. I see the mixture better with this than with Brewster's 



1 Hermann's Handhuch d. Physiologie, Bd. iii. S. 593. 

 VOL. VIII. PT. V. 21 



