660 Scientific Intelligence. 



Price $1.00 net). — This little book is one of a series of " Quiz- 

 compends" which are intended for the use of students in prepar- 

 ing for examinations. The volume under consideration gives a 

 summary of inorganic and organic chemistry, including urinary 

 analysis. As small print is used, and as the style is concise, a 

 large amount of ground is covered. The book should be service- 

 able for the purpose of reviewing the subject, and it must be 

 admitted that a student having a good knowledge of its contents 

 should be well prepared for an examination. h. l. w. 



7. /Sounds Resulting from Firing Modern Cannon and 

 Rifles. — The following statements are derived from a short paper 

 by M. Agnus entitled "Le claquement de la balle et de l'obus." 

 Since the beginning of the present European war the combatants 

 have frequently observed a curious and unfamiliar acoustical phe- 

 nomenon. It consists in an apparent repetition of the report of 

 the gun. The French designate it as the claquement of the shot 

 or shell. In general, when an observer is situated in the imme- 

 diate vicinity of the trajectory of a projectile which has a velocity 

 appreciably greater than the velocity of propagation of explosion 

 waves in air, he hears two abrupt sounds very close together. 

 The first aural impression is caused by the disturbance arising 

 from the passage through the air of the rapidly moving projectile. 

 The wave-form is somewhat similar to the resultant V-w'ave pro- 

 duced by a high-speed motor boat coursing over smooth water. 

 The second sound is due to the arrival of the explosion wave 

 which started from the muzzle of the fire-arm at the same instant 

 that the projectile left the rifle. In the original paper an instruc- 

 tive diagram is given showing the successive positions of the first 

 approximately hyperboloidal envelope and of the second lagging 

 spherical explosion pulse. This figure and the following numeri- 

 cal data pertain to the " 75 obus a balles " at different distances 

 in front of the cannon. The time intervals corresponding to 100, 

 500, 1000, and 2200 meters are given as 0*1, 0-5, 0-8, and 1*2 sec, 

 respectively. Beyond 2200 meters this projectile loses headway 

 sufficiently, due to the resistance of the air, to cause the time 

 intervals to decrease. 



It may also be worth while to mention two other cases in which 

 the same causes are operative. Agnus says that target recorders 

 are acquainted with this phenomenon but are unable to explain it. 

 They think simply that one of the sounds is due to the ball which 

 penetrated the target or struck the ground ; but they do not take 

 into account the fact that if a ball is lost in the air without touch- 

 ing any solid object the two reports are perceived just the same. 

 Again, accurate accounts of the fall of meteorites contain, with- 

 out exception, the statement that a formidable detonation was 

 heard. In general, it is said that the meteorite produces an 

 explosion or that it bursts with a tremendous noise. If, however, 

 the matter be looked into more carefully, it is found that the 

 aerolite has not burst "the least bit in the world" and it is often 

 buried in soft soil which would greatly diminish the sound of the 



