70 THE NEW WORLD OF SCIENCE 



corps, and such a company furnished two sound- and two 

 flash-ranging sections, each section forming a unit capable of 

 covering a front of about five miles. Since an American army 

 normally consisted of five corps, this gave a battalion of five 

 ranging companies per army, and this battalion, if necessary, 

 could cover with both sound- and flash-ranging a front of fifty 

 miles. An army of five corps is not likely to have to cover so 

 wide a front as this even in defensive operations, while in of- 

 fensive operations on a narrower front the, reduction in the 

 necessary number of the ranging-sections could take care of 

 the increase in the number of men required to run a section 

 under battle conditions. Under the conditions of trench war- 

 fare, four officers and from fifty-five to sixty men were found 

 to be sufficient personnel for a sound-ranging section. One 

 officer is in charge of the maintenance and repairs of the rela- 

 tively large network of electrical lines running across the 

 shelled area to the observation stations. Two officers are 

 needed, besides the commanding officer, to supervise the work 

 at the central or calculating station where three eight-hour 

 shifts are maintained and from which reports of hostile fire 

 or directions for ranging the fire of friendly guns are tele- 

 phoned to the artillery information officer. On an active front 

 two more officers and about twenty more men are needed. 

 About one-third of the men in a section are needed for mainte- 

 nance of the electrical lines of communication, another third 

 for calculation, instrumental work and forward observation 

 and the remaining third for transportation, supply, cooking, 

 orderlies, etc. The policy adopted was to keep the minimum 

 number of men necessary for proper observation at a section, 

 with reserves at company and battalion headquarters ready to 

 be sent where most needed. 



PRINCIPLES OF SOUND-RANGING 



Sound travels in still air at zero degrees centigrade, (the 

 freezing point of water), at the rate of 330.6 meters per sec- 

 ond (rcughly iioo feet per second). At 10 degrees cent, the 



