74Q 



NA TURE 



[December 2, 1922 



correcting the spherical aberration and the other for 

 correcting the astigmatism. This is usually the 

 method adopted by Rudolph in the earlier of the 

 Zeiss lenses and several of the recent lenses by other 

 makers. 



I [ugo Schroeder and Stuart, of Ross and Co.. were the 

 first to take advantage of the new Jena glasses, and in 

 1888 they patented the " concentric " lens, composed 

 of a flint and a barium crown. It was corrected for 

 astigmatism, but had a lot of spherical aberration. 

 Dr. Clay reviews briefly the series of Zeiss lenses — 

 Planar, Protar, Unar, and Tessar — made by Ross under 

 license, and in this connexion tells the following 

 significant story : 



In 1 1 1 1 1 , when Zeiss had finished their factory at 

 Mill Hill, they gave Ross notice to terminate the 

 license, and themselves made the Tessar — the only 

 one of which the patent was still running. This is 

 rather an illuminating fact. It must be remembered 

 that in 1892, when Ross started making the Zeiss 

 lenses, Ross had a great name as makers of photo- 

 graphic lenses, while Zeiss's were practically unknown 

 in that connexion, and undoubtedly Ross's reputation 

 helped to make the new lenses known ; yet no sooner 

 are Zeiss ready to make their lenses over here than 

 they terminate the contract ! No further comment 

 is necessary. 



An interesting summary follows, which we have not 

 space to notice in detail, of a brilliant series of lenses 

 produced by Ross from 1892 to the present day. 

 Dr. Clay says : " One other achievement of this firm I 

 must refer to. When the Air Force began to take 

 aerial photos in the war they found the Ross-Zeiss 

 Tessar, of 8 J, -in. locus, suitable, but soon wanted great 

 numbers, and also asked for a longer focal length lens 

 with perfect definition over a small angular field, e.g. 

 a 20-in. lens to be used with a 5 by 4-in, plate. This 

 was wanted urgently, and in a single fortnight the lens 

 was recalculated, and the ' Airo-Xpres ' lens evolved 

 in November 1918, working at f/s - 6. Messrs. Taylor, 

 Taylor and Hobson also made a variety of the Cooke 

 lens, the ' Aviar,' for the same purpose." 



We have not space to deal more than hurriedly with 

 the fascinating record that Dr. Clay gives of the other 

 work done in Britain in the development of the photo- 

 graphic lens to its present stage of wonderful achieve- 

 ment. An interesting account is given of the lenses 

 introduced by the firm of Dallmeyer, and spei ial 

 attention is directed to the striking advance repre- 

 sented by their telephoto lenses. The original patent 

 for the telephoto was taken out in 1891. Another 

 English firm, R. and J. Beck, Limited, it is interesting 

 to note, were the first to apply the iris diaphragm to 

 photographic lenses, as early as 1882. In 1906 Beck 

 introduced their " Isostigmar Universal," and in the 



following year their Isostigmar portrait lens. "These 

 lenses do not obey the Petzval condition — that the sum 

 of the power of the lenses, divided by their refraction 

 index, should be zero — and were constructed by 

 omitting this from consideration, as they believed it 

 was not essential for a flat anastigmatic field " — a view 

 afterwards confirmed by the investigations of W. 

 Elder. The Isostigmar is of interest, as it covers a 

 field of 85 to 90 degrees at f/16, the first wide angle 

 with such an aperture. Beck also introduced another 

 simple idea — the use of magnifiers in front of a lens — 

 made for their Frena camera in 1894. 



We have left till the last not the least of the British 

 achievements in the development of the photographic 

 lens — the Cooke lens invented by W. H. Dennis Taylor 

 and made and put on the market by Taylor, Taylor and 

 Hobson, Limited. Dr. Clay says : " I do not think 

 the great step which the Cooke lens marks is as well 

 appreciated here as on the Continent. The introduc- 

 tion of this lens has formed the starting-point for a 

 new method of lens construction which has had, and 

 will continue to have, many fruitful applications." 

 The germ of the invention is thus expressed by Dennis 

 Taylor : 



It . . . occurred to the author that since the 

 normal curvatures of images due to any lens, whether 

 simple or compound, are fixed by its refractive indices 

 and power alone, and are independent of the state of 

 rays entering the lens, whether convergent, divergent, 

 or parallel, then it should follow that the normal 

 curvature errors of an achromatic and aberration- 

 free collective lens should be neutralised by the 

 normal curvature errors of an achromatic and 

 aberration-free dispersive lens of the same power 

 (and made of the same glasses), placed at a consider- 

 able distance behind the collective lens ; while the 

 combination would, as a result of the separation . . . 

 yield a positive focus. . . . 



The patents for the Cooke lens were taken out in 

 1893. 1895, and 1898. During the war the special 

 Aviar lens, referred to above, was evolved, designed 

 by Arthur Warmisham of Taylor, Taylor and Hobson. 

 It is a split-divergent lens, which was a conception of 

 the inventor of the Cooke lens, but the exploitation 

 of the idea was left to Warmisham, who was able, by 

 making a special study of coma, to improve upon the 

 large aperture Cooke lenses, and secure a flat field of 

 larger area than had hitherto been found possible. 



In a brief review of Dr. Clay's lecture we have had 

 perforce to omit much of important interest, but we 

 may conclude by re-echoing the words of the author : 

 " In this story I think we in Britain may claim that we 

 have borne our share, in spite of all the praise that has 

 been lavished on the Germans." 



Obit 



Prof. Heinrich Rubens. 



HEINRICH RUBENS was born at Wiesbaden on 

 March 31, 1865, and received his early training at 

 1 he Realgymnasium at Frankfurt on the Main, where he 

 gained the School Leaving Certificate, equivalent to 

 Matriculation, in March 1884. In the summer term 

 ol that year he proceeded to the Technical High School 



NO. 2770, VOL. IIO] 



u ary. 



at Darmstadt to take up the study of electro-technics. 

 During the following winter term and the summer 

 term of 1885 he continued his studies at the Technical 

 High School at Charlottenburg, but soon recognised 

 that his ability and interest lay in the domain of 

 pure science, and for this reason he began the study 

 of physics. After spending the winter term (1885-86) 

 at the University of Berlin, Rubens passed on to Strass- 



