l
shadows, and yet which are no more real shadows than the withdrawal of
an image of a piece of white paper from a mirror is a shadow on the
mirror. Farther, in all shallow water, more or less in proportion to its
shallowness, but in some measure, I suppose, up to depths of forty or
fifty fathoms, and perhaps more, the local color of the water depends in
great measure on light reflected from the bottom. This, however, is
especially manifest in clear rivers like the Rhone, where the absence of
the light reflected from below forms an apparent shadow, often visibly
detached some distance from the floating object which casts it.

Sec. 10. Examples on the water of the Rhone.

The following extract from my own diary at Geneva, with the subsequent
one, which is a continuation of that already given in part at Venice,
will illustrate both this and the other points we have been stating.

"GENEVA, _21st April, Morning._

"The sunlight falls from the cypresses of Rousseau's island straight
towards the bridge. The shadows of the bridge and of the trees fall on
the water in leaden purple, opposed to its general hue of aquamarine
green. This green color is caused by the light being reflected from the
bottom, though the bottom is not seen; as is evident by its becoming
paler towards the middle of the river, where the water shoals, on which
pale part the purple shadow of the small bridge falls most forcibly,
which shadow, however, is still only apparent, being the absence of this
reflected light, associated with the increased reflective power of the
water, which in those spaces reflects blue sky above. A boat swings in
the shoal water; its reflection is cast in a transparent pea-green,
which is considerably darker than the pale aquamarine of the surface at
the spot. Its shadow is detached from it just about half the depth of
the reflection; which, therefore, forms a bright green light between the
keel of the boat and its shadow; where the shadow cuts the reflection,
the reflection is darkest and something like the true color of the boat;
where the shadow falls out of the reflection, it is of a leaden purple,
pale. The boat is at an angle of about 20 deg. below. Another boat nearer,
in deeper water, shows no shadow, whatsoever, and the reflection is
marked by its transparent green, while the surrounding water takes a
lightish blue reflection from the sky."

The above notes, after what has been sa