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THE POPULAR SCIENCE MONTHLY. 



the anatomy and physiology of those sys- 

 tems, and to tinderstand 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 ac- 

 quainted with the construction and opera- 

 tion of the heart and the lungs. Were 

 women trained in the knowledge of element- 

 ary 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 

 tliat 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 look- 

 ing-glass is clear ; to superintend the puri- 

 fication of the water ; and to see that sun- 

 light 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 cook- 

 ing. 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 re- 

 lating to the periods of incubation of those 

 diseases, and to have the best methods of 

 preventing disease at their fingers' ends. 



Sound-Signals. Mv. E. Price-Edwards 

 recently delivered before the Society of Arts 

 a valua'ole lecture on "Signaling by Means 

 of Sound," in which he considered the requi- 

 sites 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 modi- 

 fied 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 w"hich the ear is 

 best adapted. Bells have been long in use 

 to give signals, but their sounds are curious- 

 ly fluctuating, and it is not probable that 

 the vibrations from the largest bell are of 

 suflScient 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 ob- 

 stacles 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 repe- 

 tition of sound is wanted. Mr. J . R. Wig- 

 ham, of Dublin, has invented a gas-gun, 

 which can be loaded and fired at a consider- 

 able 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 load- 

 ed with an explosive mixture of gas and at- 

 mospheric air, fire is applied at the short 

 end of the tube, and the explosion takes 

 place at the mouth of the gun almost imme- 

 diately. 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 em- 

 ployed to explode that substance in the or- 

 dinary way is, however, cumbrous, and can 

 not be used conveniently where speedy ma- 

 nipulation 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 down- 

 ward into places which would be com- 

 pletely hidden from the level at which a 



