Page:Popular Science Monthly Volume 14.djvu/855

Rh over the aperture a film of soapsuds. By turning the wrist, the angle made with the direction of the light may be readily adjusted; a motion of the elbow alters the distance from the mouth, and the tension of the film can be exactly regulated by moving the thumb and finger. On singing or speaking to the film when in proper tension, beautiful figures appear, which may be reflected direct from the film on a screen. The experiment is extremely curious and interesting.

George Bidder, the "Calculating Boy."—There died lately in England a man of prodigious arithmetical power, whose mental faculties would afford matter for profound research to the psychologist. George Bidder made his mark in early life as a "calculating boy"; but in him one overgrown faculty did not eclipse all the other mental powers, for throughout life (he died aged seventy-two years) he evinced first-rate business ability, and in fact accumulated a large fortune by his own exertions. Nor did his mathematical faculty decline as his other powers matured; to the last he was capable of the same astonishing feats of calculation which made him remarkable as a boy. Instances of his extraordinary powers are given in a letter written by James Elliot, Professor of Mathematics in Queen's College, Liverpool, who was Bidder's fellow student in Edinburgh. Of these we quote two: A person might read to Bidder two series of fifteen figures each, and, without seeing or writing down a single figure, he could multiply the one by the other without error. Once, while he was giving evidence before a Parliamentary committee, counsel on the opposite side interrupted him with, "You might as well profess to tell us how many gallons of water flow through Westminster Bridge in an hour." "I can tell you that too," was the reply, and he gave the number instantaneously.

Certain interesting facts are mentioned with regard to the possession of the same or similar powers by members of Bidder's family. His eldest son, who is a successful barrister, can play two games of chess simultaneously without seeing the board. Like his father, he can multiply fifteen figures by fifteen without seeing them, but by a peculiar process. One of the grandsons showed a very marked degree of mechanical ingenuity. Even the granddaughters possess extraordinary powers of calculation. George Bidder's elder brother, a Unitarian minister, was not remarkable as an arithmetician, but had an extraordinary memory for Bible texts, and could quote almost any text in the Bible, and give chapter and verse. Another brother was an excellent mathematician, and was actuary of a great life-insurance company.

Peruvian Antiquities.—In an article on Peruvian antiquities, published in the "Kansas City Review of Science and Industry," Dr. E. R. Heath gives an interesting account of the vast wealth of ruins with which the land of the Incas is overstrewed. Go where you will in Peru, and relics of the past meet your eye either in ruined walls, watercourses, terraces, or extensive areas covered with broken pottery. Dr. Heath takes as an illustrative instance the Jequetepeque Valley. Here the bottom-lands of the river are from two to three miles in width, with a southern sloping bank, and the northern a perpendicular one nearly eighty feet high. Beside the southern bank, near the point where the river empties into the sea, is an elevated platform, one quarter of a mile square and forty feet high, all of adobe. A wall, fifty feet wide, connects it with another distant a few hundred yards, which is 150 feet high, 200 feet across the top, and 500 feet at the base, and nearly square. This latter structure was built in sections or rooms ten feet square at the base, six feet at the top, and about eight feet high. These rooms were afterward filled with adobes, then plastered on the outside with mud and washed in colors. All the Peruvian mounds of this class have on the north side an incline as a means of access. On the north side of the river, on the top of the bluff, are the ruins of a walled city two miles wide by six miles long. In following the river to the mountains you pass ruin after ruin, one artificial mound (huaca) after another. At Tolon, a town at the base of the mountains, the valley is crossed by walls of bowlders and cobble-stones, ten, eight, and six feet high, one foot to eighteen inches wide at the top and two to three feet at the base,