64 THE NEW WORLD OF SCIENCE 



how the enemy guns are quickly located in rain, fog or mist ; 

 for it has been the policy of the general staff to keep very 

 secret the details of a scientific service in which the Allies 

 possess a very decided superiority over the Germans. 



Let us look for a moment at what may be happening on the 

 same night on the other side of No Man's Land. A German 

 battery begins to shell an important cross-roads in the Allied 

 back area in order to prevent the bringing up of munitions or 

 fresh troops. Presently shells begin to drop from somewhere 

 in France, but at first these are not close enough to make it 

 sure that they are trying to " find " the German battery ; then 

 six or eight rounds fall to the left and behind the battery ; 

 then there follows a short pause and another series of rounds 

 falls to the right and in front of the battery ; another pause and 

 the next group of rounds has crept closer and this goes on un- 

 til the battery has become the center of a steady rain of pro- 

 jectiles which makes it impossible for the crews to serve their 

 guns. 



The German battery commander knows that the Allies are 

 directing their counter-battery artillery fire by a means which 

 he himself does not have at his disposal and he knows what 

 that means is, for his Intelligence has published a number of 

 pamphlets which describe it. He also has a set of instructions 

 as to what measures to adopt if he suspects that the Allies are 

 employing sound-ranging against him in order to render it less 

 effective, but these measures are unavailing against the most 

 improved form of apparatus operated by the Allies. 



It is the purpose of the following article to explain in non- 

 technical terms how the Allies applied certain acoustic prin- 

 ciples to determine the position of enemy guns when the more 

 usual and simpler visual means of observation failed because 

 of bad weather or because the German batteries were hidden 

 from view. It is in no sense the purpose to magnify the im- 

 portance of American scientific achievement in the war, for 

 the present writer, who as an American scientist has every in- 

 terest in seeing that all due credit comes to his profession, 



