SCIENCE AND INDUSTRY. 
continuously for a short interval a series of ether waves, these waves 
can be picked up over long distances by devices installed in a land 
station, .the direction of the source of these ether waves can: be ascer- 
tained, and in a minute or two the land station can give the observer 
of the emitting source his bearing within two degrees relative to the 
fand station. With two land stations, it is possible to obtain cross- 
bearings, and the latitude and longitude of the sending air or surface 
ship can be determined with a high degree of accuracy. 
With directional devices installed on ships, it will be possible for 
two ships whose positions are known to communicate its true position to 
a ship enveloped in a fog, and situated several hundreds of miles away. 
It is obvious, therefore, from the few illustrations which have been 
given, that directional wireless will find a wide field of usefulness in 
the future in connexion with the subject of navigation. 
(g) Explosion Pressures—In the early days of the anti-submarine 
campaign, a method of destroying submarines whose approximate loca- 
tion was known was by the employment of depth charges. To use this 
means, it was necessary, first of all, to know the neighbourhood in which 
the submarine was located, and then the chasing ship would rush to 
the spot and drop or throw to some distance charges of explosive which 
detonated when they reached a definite distance below the surface of 
the water. The necessity of knowing the destructive zone of any given 
type of depth charge soon became evident, i.c., to determine the radius 
from the exploding charge, within which a submarine would be success- 
fully destroyed. The same information was important in the laying 
out and use of minefields. - Investigations were undertaken to determine 
what pressures were generated by charges of different sizes and types 
at various distances from the place of detonation. The nature of the 
pressure wave was particularly important, for upon it depends the 
“killing power” of the charge. The laws which govern the alteration 
in form and power of waves generated by these explosions had te be 
determined in order to employ depth charges and mines in the most 
effectual and economical manner. ‘The accurate determination of the 
velocity of propagation of the explosive waves generated was also 
of importance in distributing the charges, for if waves from two dif- 
ferent sources arrive at the object in different phases, the effective 
crushing power may be considerably altered. When we know what 
the effect of different charges at various distances is—what type of 
pressure wave, whether a sudden intense blow lasting a few  ten- 
thousandths of a second, or a series of less intense shocks, has the greater 
effect in destroying the submarine when under water—then we shall 
know how best to lay out our mine-fields, and what size and type of 
charges are the best and most economical to utilize under the various 
situations which may arise. - 
(h) Sound Ranging—In the course of our investigations of the 
characteristics of pressure waves generated by the explosion of charges 
in the sea, it was found that when a hydrophone was used to pick up 
the waves a good record could be obtained by the explosion of a No. 9 
detonator at least 2 miles away. The explosions due to charges 
of 2 lbs. T.N.T. have been recorded at 14. miles, and might have been 
tecorded at far greater distances, judging from the strength of the 
signals received. The explosions of 300-Ib. ‘depth charges have been 
414. 
