“You allude, I suppose, papa,” said Frederick, “to the famous concave mirrors with which Archimedes destroyed the Roman fleet.”
“Long before his time,” my uncle replied, “concave mirrors had been constructed, by which the sun’s rays were so concentrated as to burn substances placed in the focus: but those used by Archimedes were not concave, they had plane or flat surfaces, and it was by the combination of a great number that the effect was produced. For you can readily conceive that whatever portion of the solar heat can be conveyed by reflection from a single plane surface, the effect will be doubled if the rays from another plane surface be directed to the same spot. Five or six times the direct heat of the sun would set dry wood on fire; but as more than half the heat is dissipated by reflection and by other causes, we may say that eighteen or twenty small plane mirrors would be quite sufficient for that purpose. The Count de Buffon tried a great many valuable experiments on this subject; with 154 mirrors he succeeded in burning wood at the distance of seventy yards, and in fusing several metals at eight, ten, and even twelve yards, “There was another circumstance in your question, Bertha, on which I must set you right. It is true that glass has been brought to great perfection by modern skill, but glass was known in the earliest ages of which any remains of art are now extant. The mummies, for instance, which have been brought home from Egypt, are ornamented with beads and bits of coloured glass. Pliny describes the manner of making it; and there are various authorities for believing that glass was even used in windows before the third century.”
25th.—The nightingale, the next bird that appears after the swallow, has arrived, and I have twice had the pleasure of hearing the sweetness, fulness, and power of its melody.
It is supposed to visit Asia during its absence from England, as it does not winter in the south of Europe or in Africa, but is found at all times in the East, from Persia to Japan. I must acknowledge that its song is more agreeable than that of the bird we call nightingale in Brazil.
The wry-neck, and the cuckoo, which I have; just heard, arrive here very soon after the nightingale. The wry-neck is a very pretty little bird; the neck and breast are of a reddish brown, and crossed with waving bars of fine black. It sits so very erect on a branch, that its body appears to bend almost backward, while it is constantly turning its neck quite round from side to side; and it also has the power of erecting the feathers of the head like a jay. I have seen it feeding on ants, which it dexterously transfixes with the sharp bony end of its tongue; and the country people say, that the young ones, while in the nest, make a hissing sound like that of little snakes, which deters boys from plundering their nests.
There is something very cheerful in the notes of the cuckoo and the rail. They serve to mark one of the steps by which this changeful and busy season of spring steals on us with all its gradations of pleasure and interest; and which, dear mamma, I cannot help thinking preferable to the unvarying brilliancy of Brazil.
“Now Nature, soothed, assumes her wonted charms,
And like an infant, stilled, laughs through her tears,
That glittering hang on every bloomy spray.
The birds their woodland minstrelsy renew,
In chorus universal; while the sun
Gilds with effulgence sweet the azure vault,
And paints the landscape with a thousand flowers.”
I have seen the mole cricket to-day; it is a most remarkable insect, endowed with wonderful strength, particularly in its fore legs which are fitted for burrowing. The shanks are broad, and terminate obliquely in four large sharp claws, like fingers; and the foot, which consists of three joints, and is armed at the extremity with two short claws, is placed inside the shank so as to resemble a thumb, and to perform its offices. The direction and motion of these hands enable the animal effectually to remove the earth when it burrows under ground; and in wet and swampy situations, which it loves, it excavates very curious apartments.
There is the prettiest variety of wild flowers now in bloom all over our part of the forest; not gaudy and dazzling, like the natives of the Brazil forests, but small and delicate, and beautifully marked and tinted. I am sorry to say the primroses are fading; but wild violets, the wood anemone, and millions of cowslips with their pretty golden bells, make up for their loss.
I had almost forgotten to tell you that the buds and leaves of the branches I had in water, have all withered away; ashamed, I suppose, to appear now that there are abundance of real leaves.