Page:Popular Science Monthly Volume 8.djvu/394

380, and then cautiously crawls about the jar with antennæ extended. On approaching the piece of meat, and before touching it, the animal gives a powerful backward jump and remains quiet for a while. It often repeats this three or four times before touching the food, and when it does touch it the result is another backward jump. When it has become satisfied that there is no danger, it takes the morsel in its claws and conveys it to its mouth. "I have twice," says the author, "seen the meat dropped as it was passed along the base of the antennæ, as if the sense of smell, or more delicate organs of touch seated at that point, were again the cause of alarming the animal. When the jaws once begin to work, the piece of meat, or bread, if very small, is devoured, but if too large, only a few bites are taken, and the food is dropped and not touched again."

A detailed account is given of one of the specimens, in order to show the mode of reproduction of lost members. This specimen, a female, was captured November 13th, being then perfect in all respects, except the right, large claw, which was as yet rudimentary. Total length of the animal from tip of large claw to end of tail, not quite two and a half inches. From November 14th to 24th, the crawfish lost in battle most of her antennæ, the third, fourth, and fifth legs from the left side, the fifth from the right side, and the two end-joints of the third leg on the right side; January 28th or 29th she cast her shell and came forth with a soft white covering, which was nearly two weeks in hardening. All the legs which were perfect before were now of the same size, but in addition the great claw of the right side was developed to about one-half or two-thirds the size of its fellow, and was apparently of as much use. The two missing joints of the third leg on the right side were also developed, though not quite to their full proportions. The fifth leg on the right side, and the third, fourth, and fifth of the left side, were reproduced, but in a very small and rudimentary manner. The antennæ were about two-thirds their full size. On April 20th the shell was again cast; the crawfish had now all the legs and claws nearly perfect. The great claw of the right side was very nearly as large as that of the left. The tip of the third leg of the same side was perfect, and all the legs that before were rudimentary were now developed apparently to their full proportionate size, with the exception of the last on the right side. Antennæ about full length.

From these observations, it will be seen that the parts are not reproduced in perfection on one shedding of the shell, but that each time the shell is cast they are more nearly perfect than before.

Sound and Fog Signals.—Among the papers read at the Philadelphia meeting of the American Academy of Sciences, was one by Prof. Henry on "Sound and Fog Signals," of which we present an abstract. The author stated the results of experiments made last summer, under the direction of the Lighthouse Board, at Block Island, and at Little Jail Island, at the east end of Long Island Sound. One set of experiments was made to investigate the cause of an echo apparently heard from the ocean: the results were not such as to solve the problem, though they favored the hypothesis that the echo was due rather to a reflection from the waves than from the air. Another set of experiments was directed to investigating the effect of elevation on the hearing of sound; the result was to show that a sound traveling against the wind is heard farther away on an elevation than at the sea-level. In five cases, sound was heard five times farther with the wind than against it, the wind's velocity being about five miles per hour. The effects of sound traveling with the wind, against it, at right angles to it, etc, were shown in diagrams representing curves of audition. In still air these curves are nearly circular; with wind uniform in velocity throughout the whole space the curves are approximately elliptical. The curves differed according to the different conditions. It appeared to be demonstrated that sound is heard farthest with a moderate wind, and that with a strong wind it is heard a less distance in every direction than in still air, and perhaps to a less distance than with a wind of moderate velocity. These experiments will be resumed next summer.

Origin of the Numerals.—Having never met with any explanation of the origin of