"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.