154 MR JAMES DEWAR AND DR M‘KENDICK ON THE 
arrived at a tolerably stable condition, the natural electro-motive power is in the 
first place increased, then diminished ; during the continuance of light it is still 
slowly diminished to a point where it remains tolerably constant ; and, on the 
removal of light, there is a sudden increase of the electro-motive power nearly 
up to its original position. 
TV.—EXPERIMENTS AS TO THE ACTION OF THE VARIOUS RAYS OF THE SPECTRUM. 
With the view of observing the action of the various rays of the spectrum, 
we attempted, in the first instance, to place the eye in different parts of the spec- 
trum produced by interposing a prism in the path of a beam from a lime light. 
We made numerous observations in this way. Another, and more satisfactory 
method was to pass light through a rectangular glass vessel, about one inch in 
thickness, containing a coloured liquid, the absorptive powers of which had been 
previously determined by the spectroscope. Both of these methods produced 
substantially the same results, which will be seen in the following record of 
observations made on the eye of a frog, which was in the condition giving a rise 
on the impact of light and a fall on its removal:— 





Effect of light on the Eye. : 
Obser- Beam passed Absorptive effect of fluid 
vations. through. on the Spectrum. Before On {Removal} Effect of Effect of 
impact. | impact. | of light. impact. removal, 
140 200 | 220 | 200 | Rise of 20 | Fall of 20 
141 Water. None. 200 220 200 | Rise of 20 | Fail of 20 
142 210 225 220 | Rise of 15 | Fall of 5 
143 Beeheneietoe ot Absorbs all beyond | 220 230 222 | Rise of 10 | Fall of 8 
EC aes eng the low green—| 220 | 230 | 220 | Rise of 10 | Fall of 10 
145 ee red light. 220 | 230 | 220 | Rise of 10 | Fall of 10 
146) ( Absorbs all the yel- | 226 230 227 | Rise of 4 | Fallof 3 
low, orange, and a 
Chrome alum. portion of the low | p98. |..939.| 228 | Rise of vas | (raion 
green, leaving low 
| red and violet-— 
148 | rose tint. 226 230 | 227 | Riseof 4 | Fall of 3 
149 . 4 230 | 238 225 | Rise of 8 | Fall of 13 
130 Neniray pte, | | Bbeerts al Seve aa) al 221 | Bitee af le wana 
151 ( ave aaa ey 221 | 232 | 221 | Rise of 11 | Fall of 11 
152 | a 221 | 232 | 220 | Rise of 11 | Fall of 12 
153 : 235 | 239 | 234 | Rise of 4 | Fallof 5 
ia Se ne NE betow { 237 | 241 | 236 | Rise of 4| Fallof 5 
155 Peal Peo i ee 1 240 | 244 | 239 | Rise of 4 | Fallof 5 
156 ss Ga 241 | 246 | 241 | Rise of 5 | Fallof 5 
157 Low and high end} 246 250 246 | Rise of 4] Fallof 4 
158 Sulphate of of spectrum ab-| 244 250 246 | Rise of 6 | Fallof 4 
159 nickel. sorbed — green! 249 260 250 | Rise of 11 | Fall of 10 
160 light. 250 | 261 251 | Rise of 11 | Fall of 10 
161 ‘WiFakemis hedua te 256 | 270 | 257 | Rise of 14 | Fall of 13 
162 ed ‘ None. 255 | 270 | 255 | Rise of 15 | Fall of 15 
163 ‘ 255 | 269 | 255 | Rise of 14 | Fall of 14 








