Leaf and Stick Insects.—The leaf insect and the walking-stick insect are curious creatures. All of the family to which they belong are nocturnal in habit, and spend their days resting on trees and bushes the leaves of which form their food. They so resemble the leaves and twigs as to escape all but the very keenest observation. In the leaf insect, the head and thorax form a stalk, while the abdomen, which is flat, thin, and much dilated, exactly resembles a leaf. The six legs have broad, membranous appendages on the upper part, which are especially noticeable on the fore-legs; so that the creature while resting has the appearance of a leaf that has been gnawed on both sides by a caterpillar. While the color of the insect varies at different periods of its life, it always more or less resembles a leaf at some stage; when settled on the leaves and eating at them, its body becomes bright green. After death it becomes brown like a dry leaf. The stick insects are common in the tropics, which are the principal habitat of the leaf insects, and are also found in temperate regions, including the United States. The tropical species are the largest, some of them reaching nine or ten inches in length. They are hatched from the egg in a form closely resembling that of their parents, coming into the world with three pairs of legs, which keep their shape with but little, if any, alteration during their entire existence, and which are all walking limbs. At all stages of their life they closely resemble sticks and twigs, either green and growing, or brown and withered, from which they obtain their name. They are also called specters, from their skeleton-like appearance and their slow, stealthy movements. A colony of these insects in the London Zoölogical Gardens is breeding prosperously.
Fort Ancient.—Mr. Warren K. Moorehead gave the American Association an account of his excavations of Fort Ancient, Ohio, and what he found there, in which he more fully elaborated the theory of the history of that work which was indicated in the volume upon it that we have recently reviewed. One of the points of this theory, based on the comparison of the potteries and implements found in and around the fort, and the burials, was that it was a point of contest, or battle-ground, between two races of men. Other questions occupied the author's mind as he considered the subject, and years, he said, might be spent in careful excavation of the graves and cemeteries, and there would still remain sufficient material to engage the attention of antiquaries for a long time to come. "This great inclosure, so rich in facts, so productive of implements that tell us of the every-day life of the ancient people who lived within its walls, may yet reveal to the patient investigator a history that shall go far toward dispelling the darkness that surrounds the origin and movements of ancient men on the American continent." The site has been bought by the State of Ohio, and will be preserved as a State park.
The Spectra of the Metals.—A paper by Prof. Rowland, of Johns Hopkins University, on The Spectra of the Metals, was received by the Physical Section of the British Association as a most important advance in our knowledge. The author had undertaken during the past year the measurement of the wave-lengths of the lines of nearly all the metallic spectra, and had compared them with the solar spectrum, in order to ascertain which metals were certainly present in the sun. The object of the research was primarily to find out what sort of thing3 molecules are, and in what way they vibrate. This can be deduced from the wave-lengths of the light emitted if we can find any relation between these wave-lengths. If the molecules are spheres, we should have a series of bands getting gradually nearer together toward the violet, and representing harmonics of one fundamental vibration. A spheroid or ellipsoid would give a similar crowding, but not so uniformly arranged. The author had worked on a larger scale than in any previous observations, with negatives twenty feet long for the whole spectrum, lie looked for and found many indications of the truth of the periodic law, which points to the fact that similar chemical substances have molecules vibrating in a similar manner. As examples, nearly every line in the spectrum of zinc has a corresponding one in that of cadmium; so also with calcium, strontium, and barium, and with potassium, cæsium, and rubidium. In
