PHYSIOLOGICAL ACTION OF LIGHT. too 
These experiments show—(1), that the part of the spectrum which to our con- 
sciousness is the most luminous, namely, the yellow rays, produce the greatest 
effect in altering the electro-motive force of the retina; (2), that if we divide 
the spectrum into two parts, as, forexample, into one portion above the high 
green, and another portion below the high green, the summation of the effects 
produced is about equal to that of white light; and (3), that certain of 
the colours of the spectrum may be arranged in the following order, in their 
ereater relative power in altering the electro-motive force—yellow, green, 
red, blue. 
VY .—CRUuCIAL EXPERIMENT AS TO THE EFFECTS OF LIGHT ON TWO EYES PLACED ON THE 
GALVANOMETER CUSHIONS IN REVERSED POSITIONS. 
Two eyes of the same frog were dissected out in the ordinary way. The ° 
first, which we will call No. 1, was so placed on the cushions as to give a 
deflection of nearly 400° to the right (the observer being supposed to be seated 
with his back to the galvanometer and his face to the scale). The other eye, 
No. 2, was placed in the reversed position. A current was thus obtained from 
No. 2, which passed through the galvanometer in the opposite direction to that 
of No. 1; but as the current of No. 1 was stronger than that of No. 2, the 
deflection of No. 1 was only considerably reduced. It is evident that we could 
now study the effect of light on No. 1 by placing a small black paper cap on 
No.2, and vice versd. The effects were what might have been anticipated. 
When one eye was thrown out of gear by not being subjected to the action of 
light, the deflection produced by the electro-motive force of the other eye was 
altered in the usual way. Suppose, for instance, that the impact of light in 
both cases produced (as in this instance it did) an increase in the electro-motive 
force, we would expect that when No. 2 was covered, the spot of light on the 
galvanometer scale would go to the right (as indicated by the rise of numbers 
in the following figures) ; whereas, if No. 1 was covered, the spot of ight would 
go to the left (as indicated by the fall of numbers in the following figures). 
That is to say, when No. 2 was covered, and No. 1 acted, light caused an 
increase in the electro-motive force of No. 1 (to the right) ; whereas when No. 
1 was covered, light caused an increase in the electro-motive force of No. 2 (to 
the left). Such was the case. 
Paper cap on No. 1, the deflection of which is to the right. No. 2 was in action. 
Obs. 164 Before light, 165 Impact, 163 Continued, 153 Removal of light, 150 
» 165 i 175 ee vc eh RE 4 160 
166 bar eae) me ad Gy f 165 
salle in 175 173 Mogae ; 160 
» 168 ie 176 ETT sr ABS p 160 
