
PHYSIOLOGICAL ACTION OF LIGHT. 151 
Obs. 81. Stationary at 100. On impact of diffuse light, rose to 104, that is, 
arise of four degrees. During continuance of light, fell to 102. On turning 
the light off, a slight and barely perceptible rise was observed. 
SERIES I].—EVYE or Froa. 
The eye having been adjusted on the clay cushions, the key was opened, and 
the spot of light reflected from the mirror of the galvanometer was at once 
deflected three inches off the galvanometer scale. Counting from the point of the 
polarity, this indicated a deflection of nearly 500 degrees. A small scale, divided 
into tenths of a millimetre, was attached to the galvanometer scale. The fol- 
lowing observations were then made :— 
1. A diffuse beam of light from a gas flame was passed through a globular 
glass jar, twelve inches in diameter, filled with a solution of ammoniacal sulphate 
of copper (blue light). 





Observations. aa On impact. | During light. ae Toren mee Ps f meeeacr 
82 oe, 59 56 58 Rise of 1:8 Rise of 2 
83 56 58 55 59 Rise of 2 Rise of 4 
84 55 56°5 54 55°5 Rise of 1°5 Rise of 1°5 
85 55 56 55 58 Rise of 1 Rise of 3 
86 58 59 56 57 Rise of 1 Rise of 1 
87 52 53 52 54. Rise of 1 Rise of 2 
88 51 52 50 53 Rise of 1 Rise of 3 
89 51 DIES 49°5 50°2 Rise of °5 Rise of °7 
90 45 46 47 48 Rise of 1 Rise of 1 
91 46°5 47 46°2 47-5 Rise of °5 Rise of 1'3 

In all of the above experiments what we term the inductive effect, that is, 
the rise in the electro-motive force after removal of the light, was well marked. 
The impact produced a rise of about two degrees ; there was a falling off during 
the continuance of light, and another rise on the removal of light. 
- 2. In six experiments (Obs. 92 to 97) a lighted match, held up at a distance 
of two feet, produced a rise on impact of about one degree, a fall during continu- 
ance of light, and another rise, or inductive effect, of one degree on the with- 
drawal of light. 
3. In all the previous experiments the glass of the galvanometer lamp was 
surrounded by a black shade, so. as to prevent diffuse light from acting on the 
eye. It was now found (Obs. 98) that simply removing this protective shade 
caused at once a rise of 1°5 degrees ; during the time the diffuse light acted on 
the eye there was a fall of about two degrees, and on again replacing the shade 
there was a rise of nearly two degrees. 
4, The following experiments were then made by acting on the eye with 
