When by these means a true surface has been obtained, finer sand is used, and then emery of increasing degrees of fineness, till the business of grinding is finished, and the plate is given to the polisher, whose operations my uncle was obliged to reserve for another evening.
20th.—Within the last few days the swallow has returned to us; I remember seeing it last autumn, but I did not notice it much.
I have observed that its motions are very rapid, and that it sometimes perches on the house, where it makes an odd little twittering noise.—It is a very pretty bird; the back and wings are black, glossed with purple; and the breast white, with a spot of dull red upon it. I have often read of swallows in poetry, and I shall be glad to watch this little summer guest, as it sports in the sunshine, or skims along the surface of the water. This species is, I find, the house or chimney swallow, and is distinguished from the rest of the tribe by a small white spot on each feather of the tail, which is more forked than any other species.
Mary tells me that these birds generally appear in England about the middle of April, though some few may be seen a little earlier; and that they remain to the end of September. Their arrival, she says, is always considered to be the harbinger of summer, as they come here from warmer climates.
See from bright regions, borne on odorous gales,
The swallow, herald of the summer, sails.
There is a remarkable conformity, my uncle says, between the vegetation of certain plants and the arrival of particular birds of passage. Linnæus remarked, that in Sweden the wood anemone blows on the arrival of the swallow, and the marsh marygold when the cuckoo sings; and a similar fact appears to have been observed in other countries also, for the same Greek word signifies both a cuckoo and a young fig, from their appearing at the same time.
These house swallows are the earliest of all the various species, as well as the most common. They build in barns, out-houses, and even in chimneys, the warmth of which they like; and they are said to pass with surprising address up and down the narrowest flues, to the depth of perhaps six feet, without soiling their wings.
All kinds of swallows, as they skim along the surface of the water, sip without stopping; but the common swallow only washes while on the wing; gliding through the pools many times together without seeming to stop.
21st.—After some little conversation about the alluvial alterations of the coast, and the changes produced in the interior by the different causes which my uncle had already mentioned, he said to us this morning, “Those alterations are so gradual that years are required to detect their operations, or to measure the rate of their progress; but the gigantic changes effected by volcanoes and earthquakes carry their desolation at once over whole districts. You have, no doubt, read an account of some of the destructive eruptions of mount Vesuvius, by which you know the city of Herculaneum was overflown with a torrent of melted lava, and Pompeii was buried, and remained concealed for many centuries under the ashes that were ejected from the crater.
“Large tracts of country seem to have been produced by volcanoes, and after the lapse of ages the decomposed lava has become a fertile soil. But even within the reach of history new volcanic mountains have been elevated, and new islands have sprung out of the ocean. Pliny and Seneca describe two marine volcanoes that raised themselves out of the water in the Grecian archipelago; and in the beginning of the last century the same thing again happened in the same place. In 1720, a small volcanic island rose out of the sea near Terceira, one of the Azores; and in 1811, among the same group of islands, another violent eruption of lava produced an island of considerable altitude; but in the following year it sunk into the ocean. In the sixteenth century the Lucrine Lake near Naples disappeared, and Monte Nuovo, a volcanic hill six hundred feet high, and four miles in circumference, rose out of the place it had occupied.