April 8, 1887.] 



8CIEWCE. 



347 



tion of this allegation, the puzzling experience re- 

 lated to me by Captain Shaler may be cited : " The 

 window-glass of the officers' quarters, at the test- 

 ing-grounds at Sandy Hook, situated some three 

 to five hundred feet to the westward of the gun 

 park shown in the picture, are liable to be shat- 

 tered by the concussion of large pieces in practice, 

 and it has been found that the glass is forced out- 

 ward at one time, and inward at another." Re- 

 garding the drum-heads as window-glass under 

 like conditions, we might find them ruptured by 

 compression from without in one instance, and by 

 distention of intra-tympanic air in another. 



All of us are aware of the difficulty of ascer- 

 taining the source of sound in a sea-fog, where 

 vapor-tension varies in a much greater degree 

 than inland. Professor Henry described the re- 

 flections of sound which here take place as 

 'acoustic shadows,' — a picturesque comparison, 

 recognizable by every one familiar with those 

 similar phenomena, namely, the reverberatory de- 

 tonations of thunder during a storm, where clouds 

 or mountain -peaks intervene. It is to the un- 

 recognizable ' vapor- peaks ' that many unexplained 

 and puzzling acoustic manifestations are due. In 

 the case of Corporal Ingram, cited, the wave from 

 the blast did not nearly so much affect the right 

 ear, which was turned toward the shell, as the 

 left one, the sound having been apparently de- 

 flected from its course by the heavy gun-carriage 

 intervening. 



Experiments are wanting to determine the 

 windage ' of balls. This must depend on their 

 size and velocity, nearness of passage, and the 

 force and direction of the wind. There seems to 

 be no doubt but that the windage of a cannon- 

 ball might rupture the drum-head of the ear. The 

 compression of the air before and around the ball, 

 I am informed by my friend Prof. A. M. Mayer, 

 is considerable ; wadthe velocity o^ the compression 

 is equal to that of the ball, which velocity may 

 even exceed that of wind itself. So an aerial 

 blow of such a mass of air, at such high velocity, 

 is probably quite sufficient to rupture the drum- 

 head. 



The size and force of modern military explosives 

 having been greatly increased of late years, much 

 more injury to the ear is likely to occur in future 

 than has been recorded of the past, though the 

 number of accidents from premature discharge, or 

 from exposure to the blast in firing breech-loading 



' ' Windage', it should be said, is a technical term used 

 in military parlance to indicate the difference in diameter 

 between the bore of a gun and its projectile. The wO' d has 

 been, perhaps improperly, adopted by writers on military 

 surgery, in which sense it refers to the impact of the con- 

 densed air surrounding a missile passing near any part 

 of the body. 



pieces, must be less than when muzzle-loaders 

 were in vogue. 



It is the experience of many officers that the 

 vibrations of great intensity which are given off 

 from some field-pieces and bursting shells, charged 

 with high explosives, are more disagreeable than 

 the heavier sounds of great guns. The metal 

 itself vibrates under these circumstances similarly 

 to a tuning-fork. 



A very disagreeable jar is imparted to the tem- 

 poro-maxillary articulation when the individual 

 is near a great gun being fired off. This is les- 

 sened, it is believed, by standing on the toes and 

 leaning forward. Some simple precaution, to be 

 employed by officers and men during artillery 

 practice, would seem very much needed, since 

 aural shock is not only painful and distressing, but 

 orders cannot be well heard while the confusion 

 lasts. 



There is probably no better protection than a 

 firm wad of cotton-wool well advanced into the 

 external auditory canal. In suggesting this pro- 

 tection, it is believed that harm can seldom take 

 place from pressure of air from within, since it is 

 known that the violent introduction of air into the 

 tympanum from the throat, by means of Politzer's 

 method of inflation, seldom ruptures the drum- 

 head ; though, if such a volume of air were sud- 

 denly driven into the external auditory canal, the 

 drum-head would in nearly all cases be ruptured. 



The writer, in finishing this account of the aural 

 injuries done by the explosion, would request that 

 other observers having experience in this direction 

 kindly communicate with him. Any knowledge 

 that may thus be contributed would be of service 

 to military surgeons, otologists, and others. 



Samuel Sexton, M.D. 



MINING INDUSTRIES AND MINERAL RE- 

 SOURCES OF THE UNITED STATES. 



Tenth census of the United States. Vol. xv.: Report on the 

 mining industries of the United States (exclusive of the 

 precious metals). By Raphael Pumpelly. Washington, 

 Government. 4°. 



This report supplements those previously issued 

 on the precious metals, and on petroleum, coke, 

 and building-materials ; and these volumes to- 

 gether constitute a very complete account of the 

 mining and quarrying industries of the country 

 for the census- year. 



The appearance of this volume, nearly two- 

 thirds of a decade after the close of the census- 

 year, is neither timely, nor creditable to those re- 

 sponsible for the delay ; for the practical interest 

 and usefulness of works of this class, except, per- 

 haps, for students of economics, diminish rapidly 



