2 8o 



NATURE 



[November 13, 1919 



photographer ; this can be done in ten seconds 

 •toy using- strong solutions. It is handed over to 

 a computer, who reads the time intervals and plots 

 the result, and the location of the battery is tele- 

 phoned to all interested. The time taken to work 

 out a result is generally from four to ten minutes 

 after the battery fires. The location is first tele- 

 phoned to the artillery, in order that immediate 

 action may be taken if desired. The neighbouring 

 sections and other units engaged in location are 

 then informed in order that results may be com- 

 pared. At the end of the day the section sends 

 in a full report of the day's work, and this is used 

 by the compilation staff employed in estimating 

 the positions and strength of the enemy artillery 

 in any particular sector. 



In 1917 and 1918 there were about thirty 

 sections on the Western front, each section 

 having four officers and forty men. The average 

 number of locations obtained per day by each 

 section was about five, though on a day when 

 conditions were particularly favourable it was not 

 uncommon for a section to get thirty, forty, or 

 even more locations. Long spells of westerly 

 weather were responsible for keeping the average 

 number .so low, because it was found impossible 

 to "sound-range" in a wind blowing from the 

 base towards the enemy guns. The sound is 

 deflected upwards in the well-known manner, and 

 fails to be recorded by the most sensitive micro- 

 phone. 



The accuracy of the results was tested in many 

 ways. After a successful advance it was possible 

 to examine the positions the enemy batteries had 

 occupied and compare them with the locations. 

 When this could not be done, an examination of 

 aeroplane photographs generally revealed the gun 

 pits, when sound ranging or other methods of 

 location had indicated the approximate battery 

 position. The average error of location, at a range 

 of 10,000 yards, was about fifty yards, though 

 naturally the conditions under which the section 

 was working affected the accuracy greatly. 

 Whenever possible, the aeroplane photograph was 

 relied on to give the exact battery position. The 

 sound-ranging results were especially valuable, 

 however, in that they gave not only the approxi- 

 mate location of the battery, but also its calibre 

 and the target at which it was firing. The shell- 

 burst was recorded as well as the gun report, and 

 so the time of flight of the shell could be found. 

 The character of the report was a clue to the 

 calibre of the piece. The area shelled could be 

 examined to find the shell fragments, and there 

 were other clues to the calibre which made it pos- 

 sible for sound ranging to give very full informa- 

 tion about any battery recorded, and this greatly 

 enhanced the value of the locations. 



The most serious of the difficulties encountered 

 by the sections were : Confusion between the gun 

 report and the shell-wave which precedes it in the 

 case of a high-velocity shell; inaccuracy caused 

 by ignorance as to the effect of wind and tem- 

 perature on the sound-wave; interruption by the 

 noise of our own artillery and the enemy bat- 

 NO. 261 I, VOL. 104] 



, teries; cutting of the lines by shell fire and traffic 



{ or by enthusiasts of other units collecting cable 

 of a very useful type; the difficulty of survey of 

 the microphone positions in a country where all 

 landmarks were destroyed; and in the final stages 

 of the war the problem of transporting and install- 

 ing the section quickly when the line moved every 

 few days. Experience solved these difficulties one 



. by one, and towards the end of the war the 

 sections reached a high state of efficiency, though 

 the limit of development had by no means been 



' attained, and it is certain that they might have 

 played an even greater part than they did in the 

 final struggle. 



The British system of sound ranging, founded 



I on the Bull recording apparatus, was developed 



■ entirely by officers of sound-ranging sections 

 working at the front. The original experimental 

 section was installed on Kemmel Hill, south of 

 Ypres, and its researches were carried out there. 

 Later, when there were sections along the whole 

 front, it was arranged that an officer from each 

 section should attend a conference which was held 

 every two months. At the conference, proposed 

 improvements were gone into, the equipment was 

 discussed, results were compared, and the report 



i of the discussion was submitted to General Head- 

 quarters. This informal conference did more than 

 anything else to improve the work of the sections 

 — it stimulated rivalry and ensured that all pro- 



' posed alterations in the existing methods were 

 subjected to severest criticism by men who had 

 first-hand experience before they were adopted or 

 turned down. The officers were for the greater 

 part university men who had had a scientific train- 

 ing, and it would not be possible to imagine a 

 more keen and enthusiastic body of men. They 

 were sorely tried in the early days of sound rang- 

 ing, when they worked under great difficulties, and 

 had yet to prove that reliance could be placed on 

 their results ; but they were amply repaid when 

 sound ranging came to its own at the end of the 

 war, and was recognised as one of our most 

 valuable means of locating the enemy's batteritis. 



1 RESULTS OF THE TOTAL SOLAR ECLIPSE 

 OF MAY 29 AND THE RELATIVITY 

 THEORY. ' 



THE results obtained at the total solar eclipse 

 of May 29 last were reported at a joint 

 ; meeting of the Royal and the Royal .Astronomical 

 Societies, held on November 6. The stations 

 occupied were Sobral, in North Brazil, and Prin- 

 cipe Island. Two cameras were employed at Sobral, 

 the 13-in. objective of the Greenwich astrographic 

 equatorial, and a 4-in. lens, of 19-ft. focus, lent, 

 together with an 8-in. coelostat, by the Royal 

 Irish Academy. It was realised, before the ex- 

 pedition started, that the coelostat was scarcely 

 suitable for observations of such extreme pre- 

 cision as were required to detect and measure the 

 small shift in the places of the stars that might 

 be produced by the sun's attraction. War con- 

 ditions, however, made it impossible to construct 



