February 3, 19 16] 



NATURE 



623 



In a patent of 1902 Dr. Common used the com- 

 bination of a collimator and a Galilean telescope, 

 much in the same way as that of Mr. Dennis 

 raylor described above, but with this difference : 

 the collimator mark was placed beyond the prin- 

 cipal focus of the lens and thus the rays emerged 

 convergent, the convergency being the same as 

 the rays within the telescope proceeding from the 

 objective. The rays were then deflected by an 

 inclined mirror and were brought to a focus on 

 the same image plane as that of the telescope's 

 objective, and could thus be viewed by the same 

 eye-piece. 



Many of the above sights have the inherent 

 tlefect of the Galilean telescope, i.e., a very small 

 field, and were merely side issues to the purely 

 telescope sight, with its large field and compact 

 form. One of the earliest telescope sights is to 

 be seen at Bisley, and was used in the U.S.A. 

 Civil War. From then onwards many attempts 

 were made to combine successfully the rifle and 

 telescope to withstand active service. By 1901 

 Common had perfected his telescope rifle sight, 

 and he was shooting at Bisley in the "Winans" 

 competition of that year with a telescope 

 sight, which to this day has not been im- 

 proved as regards the principles employed. 

 The body of the telescope was of steel, light and 

 strong, a minimum of parts was used, and every 

 fundamental part was rigidly fixed so that the 

 shock of firing could not disturb the optical axis. 

 The lenses of the eye-piece were so arranged 

 that the Ramsden circle was nearly, two inches 

 behind the telescope, so that the jerk of recoil 

 could not easily cause injury to the eye, and the 

 emergent pencil was large and easily picked up. 

 Inside the telescope a parallel plate of glass, turn- 

 ing about a vertical axis, was provided to give a 

 lateral deflection to correct for windage. The 

 whole was mounted on a base, inclinable by means 

 of a specially shaped cam to provide for elevation 

 when long ranges were required ; whilst for shorter 

 distances the telescope was fixed and allowance 

 for change of range was made by moving the 

 sighting pointer by means of a screw. The whole 

 was then so arranged that it could be in- 

 stantaneously attached firmly to the rifle near the 

 breech without interfering with the ordinary open 

 sights. 



Some German firms embodied all Common's 

 ideas in the manufacture of telescope sights, even 

 to the use of eccentric rings in which the object 

 glass was mounted for the adjustment of the axis 

 of coUimatron, but Zeiss made use of a "Leman " 

 prism, a variety of the "Porro" prism system 

 which the firm had used in the manufacture 

 of binoculars. The Zeiss prism telescope 

 sight is really a small periscope, the prism 

 system enabling the eye to be placed on 

 a lower level than the object glass. It is a 

 small instrument, but in consequence of the 

 number of reflections and thickness of the prism, 

 more light is lost in transmission than in the simple 

 telescope ; further, its shape is not conducive to easy 

 alignment. In order to obtain elevation for dif- 

 ferent ranges, the object glass is mounted in a \ 

 NO. 2414, VOL. 96] 



sliding fitting which is actuated by a milled edge 

 ring. On turning the ring a vertical motion is 

 given to the object glass and a corresponding 

 shift to the optical axis ; the ring is graduated 

 to suit the equivalent change in range. 



In the Zeiss and the similar Goerz prism rifle 

 sight, means are provided for illuminating the 

 cross wires at night. A small beam of light is 

 transmitted through the edge of the glass 

 diaphragm on which the lines are engraved ; most 

 of the light passes through the diaphragm, since 



Ku;. 8. — Zeiss p'ism ttlescope sight. 



total internal reflection is secured, except where 

 the rays strike the incisions in the glass, thus 

 illuminating them, whence they appear as bright 

 lines on a dark field. 



Later, for long-range shooting and machine- 

 guns, this sight has been mounted, by the 

 Aktiengesellschaft Hahn fiir Optik, on an elevat- 

 ing arc to obtain the various ranges, and the 

 objective made adjustable in a plane at right 



Fio. 9.— Prism telescope sight on elevating arc with lateral correction to 

 object glass for windage. 



angles to the line of vision to obtain the lateral 

 displacement for wind and other causes. 



Accurate shooting in modern warfare is essen- 

 tial, whether of rifle or machine-gun ; a hit is more 

 valuable than any number of misses. The tele- 

 scope sight is an aid to this end, but it 

 is handicapped by the fact that rifles are not 

 made with breech ends suitable for its easy attach- 

 ment, but probably its severest handicap is the 

 lack of official encouragement of the optical in- 

 dustry in this country. W. S. 



