Could that be the case? For a long while men decisively answered--No. Everybody knew that water was colourless, so the idea was flung aside as impossible. Another explanation came up instead. The sea is full of fine dust; and it was suggested that, as vast multitudes of these floating dust-particles are exceedingly small, they might be able to reflect only the smaller blue light-waves, and not the larger yellow or the still larger red waves. Thus the sea would naturally seem to be blue. After much discussion, careful experiments were made. Different objects were lowered to various depths, and the effect upon their colouring was noted. The outcome of these and other tests went far to prove that the old certainty was wrong, and that water is in itself blue. Somebody may feel inclined to protest. “Water blue! But that is out of the question. I have good sight, and I assure you there isn’t the least sign of colour in water. Not the faintest. If you dip a bucket in the sea, you will see for yourself.” Yet all the while the colour may be there, actually existent, though not to be detected by your eyes or mine in a pailful. A short time ago I had to buy a piece of lace; and my intention was to choose a pale straw or deep cream. The lace was wound in many folds round a large cardboard, and it seemed to be exactly the right hue--a rich yellow-cream, almost butter colour. Without further demur, I ordered about a yard to be cut off. On reaching home, I found myself in possession of a piece of wide dead-white lace--or all but dead-white. It was actually a very pale cream; and when a great many folds lay one over another the combined effect was rich and yellow. But a single thickness of the material showed no colouring. The same may be seen with a single piece of very pale blue muslin. It will appear to be white. But yards upon yards of the same, folded together, will become quite a deep blue. A single thin layer of ocean-water, in like manner, has too faint a hue to be visible to ordinary eyesight. It is only when layers are piled upon layers that the blue becomes distinct; and the deeper the water, the deeper generally will be the colour. Some yards of water-thickness may be said to correspond to a single thickness of lace or muslin. While, however, we may say with tolerable confidence that the blue of the ocean is a “True Blue,” this alone will not explain all the varieties of tinting, seen at different times and in different places.