403 



NATURE 



[July 24, 1919 



From this formula it will be seen that, to decrease 

 the error 8 R at a particular rang-e, either the 

 magnification M or the base length B must be in- 

 creased. In practice the magnification is limited 

 by the permissible size of the optical parts and the 

 necessity to provide for range-taking in dull light, 

 by the quality of the optical glass, and by external 

 circumstances such as mirage due to the interven- 

 ing atmosphere. At the present time a magnifica- 

 tion of more than 30 diameters is not desirable. 

 When this maximum magnification is provided, 

 the required accuracy of observation is then ob- 

 tained by increasing the base length. 



At the commencement of the war no British 

 battleship carried a rangefinder of greater base 

 than 9 ft. This base had been decided upon in 

 1904, when the maximum effective range for the 



Notwithstanding the use of 9 ft. rangefinders 

 in association with guns, the power of which has. 

 been so greatly developed during the last twelve 

 years, the British Fleet at the Battle of Jutland 

 defeated the German ships, which there is good 

 reason to belieA'e were equipped with rangefinders 

 of 20 ft. base and, probably, to some extent 33 ft. 

 base. In such circumstances it is not surprising 

 that the German rangefinding was excellent : it is 

 more surprising that it was not very much better 

 and that its excellence was confined to the first 

 stage of the action. 



It should be observed that, for a given gun, the 

 longer the range the more necessary it is to know 

 the range accurately, on account of the greater 

 angle of descent of the projectile — that is to say, 

 an error of lOO yards in range has a much greater 



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Flu. I. — Naval rangefinder type F.X. with uniform range scale accessories. Base length 30 ft.; Magnifications 16, 20, and 28; uncertainty of 

 observation under good conditions 330 yards at 40,000 yards range. 



opening of fire was generally assumed to be 

 not greater than about 6000 yards. In the Battle 

 of Jutland fire was carried out at ranges above 

 20,000 yards. The Iron Duke, which carried 

 only 9 ft. rangefinders, opened fire at 12,000 

 yards. The rangefinders were, therefore, called 

 upon to perform a duty at least four times as 

 onerous as that for which they were originally 

 designed. It will be understood that the substitu- 

 tion on existing ships of the larger types of range- 

 finders available involved extensive structural 

 alterations that could not readily be carried out, 

 and it is only within very recent years that the 

 importance of rangefinding has been recognised 

 as being sufficient to justify the ships being de- 

 signed for the accommodation of rangefinders 

 most suitable for the guns. 

 NO. 2595, VOL. 103] 



effect on the percentage of hits at 24,000 yards 

 than at 6000 yards — but a rangefinder gives errors 

 varying according to the square of the distance. 

 The problem of finding a range of 24,000 yards 

 within 100 yards is sixteen times as difficult as the 

 finding of a range of 6000 yards within the same 

 limit. 



The modern rangefinder differs from the earlier 

 types in the size of the optical parts and, conse- 

 quently, of the mechanical parts, and in the pro- 

 vision of internal adjusting devices and of such 

 accessories as variable power eye-pieces, light- 

 filters, and apparatus involving complicated conical 

 gearing for the conversion of the reciprocal scale 

 into a uniform scale of ranges. Considerable im- 

 provements have been effected in the mountings, 

 which are necessarily designed to suit particular 



