Formerly, whitebait were considered to be the young of the shad; and only of late years has the misnamed fish taken its proper position. It appears that Mr. Yarrell, the able naturalist, was one morning in March struck with the early appearance of whitebait in a fishmonger's shop in St. James's; and knowing that shads, which they were supposed to be, did not make their appearance till much later (May), he took up the matter, and persevered in a course of investigation, which lasted from March to August, 1828. The specific distinction between the two fishes, on which Mr. Yarrell relies as of the greatest value, is the difference of their anatomical character; and especially in the number of vertebræ, or small bones, extending from the back-bone. "The number of vertebræ in the shad," he states, "of whatever size the specimen may be, is invariably fifty-five, while the number in the whitebait is uniformly fifty-six; even in a fish of two inches, with the assistance of a lens, their exact number may be distinctly made out."
CATCHING ELECTRIC EELS.
Humboldt gives a very interesting narrative of the mode of the capture of the gymnoti employed by the Indians of South America. This is done by rousing the eels by driving horses and mules into the ponds which those fish inhabit, and harpooning them when they have exhausted their electricity upon the unhappy quadrupeds.
"I wished," says Humboldt, "that a clever artist could have depicted the most animated period of the attack; the groups of Indians surrounding the pond, the horses, with their manes erect, and eye-balls wild with pain and fright, striving to escape from the electric storm which they had roused, and driven back by the shouts and long whips of the excited Indians, the livid yellow eels, like great water-snakes, swimming near the surface, and pursuing their enemy: all these objects presented a most picturesque and exciting ensemble. In less than five minutes, two horses were killed: the eel, being more than five feet in length, glides beneath the body of the horse, and discharges the whole strength of its electric organ; it attacks at the same time the heart, the digestive viscera, and above all, the gastric plexus of nerves. I thought the scene would have had a tragic termination, and expected to see most of the quadrupeds killed; but the Indians assured me that the fishing would soon be finished, and that only the first attack of the gymnoti was really formidable. In fact, after the conflict had lasted a quarter of an hour, the mules and horses appeared less alarmed; they no longer erected their manes, and their eyes expressed less pain and terror. One no longer saw them struck down in the water; the eels, instead of swimming to the attack, retreated from their assailants, and approached the shore."
The Indians now began to use their missiles; and by means of the long cord attached to the harpoon, jerked the fish out of the water without receiving any shock so long as the cord was dry. All the circumstances narrated by Humboldt establish the close analogy between the gymnotus and torpedo in the vital phenomenon attending the exercise of their extraordinary means of offence. The exercise is voluntary and exhaustive of the nervous energy; and, like voluntary muscular effort, it needs repose and nourishment to produce a fresh accumulation.
SIR WILLIAM HERSCHEL'S FIRST TELESCOPE.
Sir William Herschel arrived in England from Hanover, his birth-place, about the end of the year 1759, when he was in his 21st year. He was bred a professor of music, and went to live at Halifax, where he acquired, by his own application, a considerable knowledge of mathematics; and, having studied astronomy and optics in the popular writings of Ferguson, he was anxious to witness with his own eyes the wonders of the planetary system. He accordingly borrowed of a friend a telescope, two feet in focal length; and, having directed it to the heavens, he was so delighted with the actual sight of phenomena, which he had previously known only from books, that he commissioned a friend to purchase for him in London a telescope, with a high magnifying power. Fortunately for science, the price of such an instrument greatly exceeded his means, and he immediately resolved to construct a telescope with his own hands. After encountering the difficulties which every amateur at first experiences, in the casting, grinding, and polishing, of metallic specula for reflecting telescopes, he completed, in 1776, a reflecting instrument, five feet in focal length, with which he was able to observe the ring of Saturn, and the satellites and belts of Jupiter. This telescope was completed when he resided at Bath, where he acquired by degrees, and in his leisure hours, that practical knowledge of optics and mechanics which was necessary for such a task.