the female Arabian camel; but when the parentage is reversed the progeny is useless. General Harlan is said to have marched two thousand Bactrian camels four hundred miles and crossed the Indian Caucasus in ice and snow, with the loss of only one animal, and that by an accident. This camel is native to the high plateaus, steppes, and deserts of Mongolia and South Siberia, and it has been found wild on the plain of Tsaidam, maintaining itself in this "arid, cold, and waterless region, where the herds are said to travel seventy miles to drink. Nothing," we are further told, "but too much comfort or a damp climate seems to hurt it. For food it prefers dry, salty plants and bushes and grows sick and lean on good pasture. The salty efflorescence of the steppes is eagerly eaten by it, and in this country it prefers dry food, especially wheat straw and hay. Prjevalski's camels would eat almost anything—straw, bleached bones, old pack saddles, straps, and leather. The Mongols told him of camels which had been without food a long time, and then devoured an old tent belonging to their owner. They even ate meat and fish, and one of the traveler's camels made a meal of the bird skins ready for stuffing."
Nicaragua and its Ferns.—Tropical America is described by B. Shimek, in a paper on the Ferns of Nicaragua, as the fern paradise of the earth. "No other corresponding division of the earth's surface," he says, "presents as great a total number of species, or as many species which are peculiar to it. Nowhere else is the great variation in form and size, in structural characters and habits of growth, and in the arrangement and character of the reproductive organs, better shown than here. This richness in the fern flora, exhibited in almost unlimited variety, is, no doubt, accounted for by the topography and contour of that part of the American continent which lies within the tropics. It is narrow when compared with the continents of the Old World, and it contains high mountain chains, which form its longest axis. Its narrow form brings all of it more or less within the influence of the adjacent oceans, which furnish to most of it an abundance of moisture. Its high mountains supply all the conditions effected by altitude, and, moreover, cut off the otherwise abundant moisture from certain areas. We have thus within comparatively restricted limits all the possible degrees of moisture and temperature, and the effect of environment finds abundant expression in the great variety of fern structures." After palms, ferns form the most conspicuous feature of tropical vegetation, and in size they vary from species only a fraction of an inch high to splendid tree ferns or vines single fronds of which are more than thirty feet long. In texture "some rival the flimsiest lace, while others develop thick, leathery fronds. . . . In habit the variation is fully as great. In western Nicaragua, for example, where there is a distinct dry season, ferns growing on bare volcanic rock become so dry that they may be ground to powder between the fingers, and yet they retain life; while in the eastern part, with its deep jungles in which perpetual shade and moisture prevail, the more delicate as well as the more gorgeous forms have full opportunity for the development of their many peculiarities." In a very small territory of Nicaragua, including a strip along the San Juan River in no case extending more than six miles away from it, and in the little island of Ometepe in Lake Nicaragua, Mr. Shimek, in less than four months, while engaged in general botanical work, collected more than a hundred and twenty species of ferns; and yet only about one fifth of one hundred and twenty-one species recorded by Founder, two fifths of one hundred and thirty-five species credited by Hemsley to Nicaragua, and two fifths of those reported by Baker and Hemsley from adjacent Costa Rica, occur in his list.
Wave Length and other Measurements.—Describing the measurement of absolute wave length before the Astronomical and Physical Society of Toronto, Mr. A. F. Miller remarked that a somewhat incorrect idea prevailed as to the smallness of the space occupied in the performance of luminous undulations; in fact, some people seem to regard the wave length of light as something almost inconceivably small. Really, however, we are familiar with much smaller dimensions. For instance, the author had found from actual measures that the wave length of one of the characteristic lines in the spectrum of sodium vapor was very nearly