November 13, 1919] 



NATURE 



279 



Our attention was directed to the French results 

 in the early part of 191 5, and a proposal to form 

 an experimental sound-ranging section was laid 

 before the Experiments Committee at General 

 Headquarters. The committee at first decided 

 against ordering any apparatus, but was per- 

 ■ suaded to alter its decision, and an English sound- 

 ranging section was sent to the front in October, 

 191 5. Sound ranging was still in its infancy, and 

 the results obtained were very disappointing. In 

 fact, it was doubtful at one time whether the 

 continuation of the experiments would be author- 

 ised. Fortunately, sound ranging just survived 

 these early trials, and during 1916 sufficient 

 sections were formed to cover the whole front. 



The apparatus which we adopted was designed 

 by M. Bull, of the Institut Marey, in Paris, and 

 was one of several with which the French -Armv 



Report reaches No. i microphone. 



4- 



Report reaches No. 6 microphone. 



..one second.. 



Fig. 2. — The figure U an enlarged print of the record of a 15 cm. howitzer, 

 the report of which ha.s reached No. i microphone first and No. 6 micro- 

 phone last. Tlie film has been moving Irom right to left while the record 

 was being taken. The time intervals are marked by vertical lines, one 

 hundred to the second, every tenth line being heavier so as to facilitate 

 counting. The horizontal lines represent the shadows of the Einthoven 

 strings, which lie across the slit behind which the film is exposed, and 

 the movements of which are shown on the record. 



was experimenting. It is not possible to describe 

 the apparatus fully. The recording apparatus con- 

 sists of an Einthoven galvanometer with six 

 strings, each string being connected to a micro- 

 phone at a receiving station. The currents which 

 the microphones send to the recording instrument 

 cause the corresponding strings to vibrate, and 

 their movements are recorded photographically on 

 a moving kinematograph film. At the same time, 

 by interrupting the light which photographs the 

 strings on the film, at intervals of i/ioo second, 

 a series of time markings is ruled on the film, 

 which makes it possible to measure the time 

 interval between the arrival of the sound at two 

 stations. The microphone finalh' used was of a 

 special type adopted after experiments at the 

 front. Its special feature is that it is very sensi- 

 tive to sounds of long wave-lengths, such as gun 

 reports or shell bursts (the wave-length of the 

 NO. 261 1, VOL. IO4I 



report of a large gun may be 250 ft.), while com- 

 paratively insensitive to ordinary sounds, such as 

 speech, rifle fire, traffic, and so on. The credit of 

 its design is due to Lt. Tucker, an officer serving 

 in the experimental section in 1916. 



A record of a German 15-cm. howitzer is illus- 

 trated in Fig. 2. 



The installation of a section using the Bull 

 apparatus is shown in Fig. 3. There are six 

 microphones, spaced along a " base " about 

 9000 yards long and 4000 yards behind the front 

 line. These are wired up to a central station 

 which is placed in a cellar or dug-out some 

 5000-6000 yards from the front line. In front of 

 the base are the "advanced posts." An observer 



-\rea occupied by enemy batteries. 



Ffont I,iue. 



3500 Yards 



Cenfr«l Station 



Fig. -,. 



is stationed at each of these. When he hears a 

 hostile gun fired, he presses a key which sets in 

 motion the apparatus at the central recording 

 station. The kinematograph film runs through the 

 camera, the lamp is turned on, and all is ready 

 to record any sounds reaching the microphones. 

 Having allowed time for the sound to reach all 

 the microphones, the forward observer raises his 

 key and the recording apparatus stops. He tele- 

 phones to the central station a report giving his 

 estimate of the direction from which the firing 

 has come, of the target, and of the calibre of the 

 piece. The film is developed and fixed by a 



