tinguishably for some time. Besides this—whether or not this had anything to do with it—it became all at once of a lovely glaucous green colour, luminous, and with bubbles flashing about it. Gradually the form became lost, but the luminous green was never lost, and after becoming dimmer and dimmer began to get brighter and brighter again, till the bird reappeared out of it on the surface at some distance off. It seems just possible that this effect may be due in some measure to the white patches, since when the shag dives nothing of the sort, or, at any rate, nothing so marked, is to be seen, nor do I remember noticing it either in the guillemot, razorbill, or puffin, which are all dark above and only white underneath. On second thoughts, however, the colouring can have little or nothing to do with it, since the effect is very marked in the eider-duck of both sexes, and the female is uniformly dark. But how is the effect produced? by the clinging of innumerable small air-bubbles to the bird's plumage? If so, they may not cling equally to that of all species. The seal presented the finest appearance of all, but his size may perhaps have had something to do with this. Whatever may be the cause, I do not remember to have remarked the same thing in river-birds when diving. It is more difficult, indeed, to follow them under water when they dive, on account of the absence of cliffs to look down from. Still, one sees them sometimes, and, as I say, I do not remember noticing this luminous effect, so that it must be, at any rate,
