Page:Popular Science Monthly Volume 19.djvu/442

428 the anatomy and physiology of those systems, and to understand what part food plays in the economy, the relationships and effects of particular foods, and their relative adaptation to different ages and conditions of the body. Woman should also be acquainted with the construction and operation of the heart and the lungs. Were women trained in the knowledge of elementary truths about the visual function and guided by them, they would see that their children did not assume those positions in study that conduce to short-sightedness and curved spines; if they carefully studied the nature and functions of the skin, they would learn to insist upon the necessity of daily purification by the bath. Woman might also, and ought to, learn all that health requires in the construction and maintenance of the house: to maintain economically within it an equable temperature at all seasons; to keep the air free from dust; to know all about and watch all the drain-pipes, and see that they are kept as systematically clean as the china; to distinguish whether the water is wholesome and agreeable with as much facility as she determines whether the looking-glass is clear; to superintend the purification of the water; and to see that sunlight finds its way into every apartment, and that damp has no place in any one of her rooms. She ought to study the nature and uses of foods, so as to be able not only to make the best selections and carry out the best modes of preparation, but even to introduce new and improved modes of cooking. The knowledge of the diagnosis of disease is not necessary for women except in a limited degree, but they ought to know the correct names and characters of common diseases, to be acquainted with the facts relating to the periods of incubation of those diseases, and to have the best methods of preventing disease at their fingers' ends.

Sound-Signals.—Mr. E. Price-Edwards recently delivered before the Society of Arts a valuable lecture on "Signaling by Means of Sound," in which he considered the requisites of a good signal, and discussed the merits of the different signals in use. The essential quality of a good sound signal is that it shall give a strong sound which can be uniformly heard at a definite distance. The range of a sound is determined by the force with which it is uttered, and is modified by certain conditions of the atmosphere. It is also controlled in part by its musical pitch. The most effective sounds are not found among the very highest pitches, as many imagine, any more than among the very low ones, but appear to lie among the intermediate pitches, to which the ear is best adapted. Bells have been long in use to give signals, but their sounds are curiously fluctuating, and it is not probable that the vibrations from the largest bell are of sufficient intensity to yield a sound capable of overcoming opposing influences, even of a slight nature. Gongs give a distinctive sound, serviceable at a short distance, but it, too, is soon dissipated after leaving the vicinity of the instrument. Gun-signals are of great value, but, according to Professor Tyndall, they can not always be depended upon to overcome local or temporary obstacles to the propagation of sound. It is, moreover, not always convenient to place and manage guns where it is desirable to use them, or to fire them as rapidly as repetition of sound is wanted. Mr. J. R. Wigham, of Dublin, has invented a gas-gun, which can be loaded and fired at a considerable distance from the point of explosion. It consists of a tube of the desired size placed at the point where the signal is to be made, and connected with a gas-main or gas-holder by iron piping. The gun is loaded with an explosive mixture of gas and atmospheric air, fire is applied at the short end of the tube, and the explosion takes place at the mouth of the gun almost immediately. An exceedingly sudden and sharp blow is given to the air, and a sound-wave of great initial intensity is generated by the explosion of gun-cotton. The apparatus employed to explode that substance in the ordinary way is, however, cumbrous, and can not be used conveniently where speedy manipulation is wanted. A rocket has been devised to carry a charge of gun-cotton, or tonite, to a certain height, where it is caused to explode, which has been tested with the most satisfactory effects; from the height of six hundred feet, to which the rocket may be adapted, a direct sound is sent downward into places which would be completely hidden from the level at which a