There is doubtless a physiological reason for this satisfaction to the eye, as indeed there is for so many of the pleasurable sensations we experience in seeing. We may say that the vision flies over a perfectly smooth plain surface, like a ball over a sheet of ice, and rests nowhere; but that in a mosaic floor the segmentation of the surface stays and rests the sight. To go no farther than that, which is but a part of the secret, the sheet of fern fronds, on account of this staying effect on the vision, increases what we see, {65} so that a surface of a dozen square yards of fern seems more in extent than half an acre of smooth-shaven lawn, or the large featureless floor of a skating-rink or ball-room. [Sidenote: Harshening bird-voices] On going or wading through the belt of bracken under the tall firs--that billowy sea of fronds in the midst of which I have so long detained my patient reader--into the great oak wood beyond and below it, on each successive visit during the last days of June, the harshening of the bird voices became more marked. Only the wren and wood-wren and willow-wren uttered an occasional song, but the bigger birds made most of the sound. Families of young jays were then just out of the nest, crying with hunger, and filling the wood with their discordant screams when the parent birds came with food. A pair of kestrels, too, with a nestful of young on a tall fir incessantly uttered their shrill reiterated cries when I was near; and one pair of green woodpeckers, with young out of the breeding-hole but not yet able to fly, were half crazed with anxiety. Around me and on before me they flitted from tree to tree and clung to the bark, wings spread out and crest raised, their loud laugh changed to a piercing cry of anger that pained the sense. They were now moved only by solicitude and anger: all other passion and music had gone out of the bird and into the insect world. The oak woods were now full of a loud continuous hum like that of a distant threshing-machine; an unbroken deep sound composed of ten thousand thousand small individual sounds conjoined in one, but diffused and flowing {66} like water over the surface, under the trees, and the rough bushy tangle. The incredible number and variety of blood-sucking flies makes this same low hot part of the Forest as nearly like a transcript of tropical nature in some damp, wooded district as may be found in England. But these Forest flies, even when they came in legions about me, were not able to spoil my pleasure. It was delightful to see so much life--to visit and sit down with them in their own domestic circle.