persons, present different colours ; so that no proof 
of the compound nature of the green colour of plants 
can be drawn from this experiment, relating to acci- 
dental colours, as M. Haiiy seemed to suppose. 
493. The operation of electricity on the organ of 
vision, supports the view above stated, respecting ac- 
cidental colours ; for when the eye is positively electri- 
fied, objects are said to appear red, large and distinct ; 
and when it is in a negative state, they look blue, small 
and obscure *. M. Ritter placed his eye in contact 
with the negative pole of the Voltaic pile, when it 
acquired the opposite state of electricity, and the ob- 
jects all appeared of a red tint ; and afterwards, on 
applying his eye to the positive pole, which caused 
the retina to pass to a negative state, the objects all 
assumed a purple hue. Thus, the organ of sight, 
says M. Haiiy, subjected to the combined action of 
light and electricity, becomes, as it were, a eommon 
link joining together phenomena observed till then 
in isolated experiments, and with instruments which 
appeared to have no affinity with each other f. And 
do not these similar sensations of colour, produced 
by the sun's light and by electricity, support the 
analogies traced, in so many other instances, be- 
tween the operations of these subtile agents ? 
494. The mode, also, in which the green colour 
is formed in vegetable infusions, leads to the belief 
that it is truly a simple colour. When an alkali is 
added gradually to a colourless infusion, the liquor, 
* Haiiy's Elem. Phil. vol. li. p. 55. 
f Elem. Phil. vol. li, p, 260. 
