November 3, 1921] 



NATURE 



305 



and in doing so he minifies the value of Faraday and 

 Harcourt's work. Of Harcourt he says : "The result 

 at that time (between 1834 and 1844) was scarcely of 

 anv practical importance." 



Now what does Dr. Zschimmer, who until the Re- 

 olution was chemist to Messrs. Schott, of Jena, 

 ,iy? I shall translate from his book, "Die Glas- 

 iiidustrie in Jena " (p. 22), and throughout I shall 

 limit mvself to quotations from German sources : 

 With Harcourt's experiments there began in the 

 vear 1834 the systematic ' scientific melting ' of glass 

 in the laboratory. He was the discoverer of the first 

 research furnace for fusion at high temperatures, the 

 first who was able to complete numerous small experi- 

 mental melts, and thence to determine by spectro- 

 meter measurement the optical properties — refrac- 

 ion and dispersion — of various extreme glass sub- 

 -cances." 



On p. 23 he continues : " Harcourt . . . dis- 

 covered the power of molten phosphoric acid and boric 

 acid to form glass with almost all the elements, and 

 on account of their fluidity he substituted them for 

 the more viscous silica. Already in 1844 he was able 

 to communicate to the British Association the happy 

 -uccess of his first experimental melts, the further 

 'bject of which was to compare the chemical con- 

 stitution with the optical properties of different 

 glasses. ..." 



Dr. Zschimmer is generous, but not unduly so. A 

 genuine man of science himself, he has recognised 

 the great, far-reaching practical results of Harcourt's 

 work, but Dr. Zschimmer has embarrassed us. In 

 accepting his opinion we must doubt that of Messrs. 

 Zeiss 's representative, whose declared object it is to 

 "furnish some trustworthy historical data." 



Messrs. Zeiss's spokesman questions to-day the 

 statement in Nature that : " If the British optical 

 industr>^ is to be maintained and to develop so as to 

 turn out products equal at least to the best products 

 ■of other nations, it must not be dependent on foreign 

 sources for the supply of optical glass, but must have 

 an adequate home supph', equal, again, at least to 

 the best available anywhere." " Historv," he says, 

 "does not point to the existence of such a ven' close 

 relation between the welfare of the glass-founder 

 and of the optical instrument-maker in the same 

 country." 



Does it not? Is Messrs. Zeiss's publicity manager 

 so unfamiliar with the history or the Jena establish- 

 ments? If in the above statement from Nature the 

 ■word " German " be substituted for " British," we have 

 the essence of the original appeals for a subsidv made 

 to the Prussian Government. In this connection I 

 shall translate part of a vigorous statement made by 

 Rudolf Virchow : " It concerns itself, indeed, with a 

 national undertaking, the object of which is to pro- 

 duce in Germany in an independent wav the glass 

 necessar\- for all scientific purposes, and also to provide 

 for the population what is necessars" for the produc- 

 tion of spectacle glasses, opera glasses, and the like. 

 Nevertheless the latter is not the principal object. It 

 concerns itself, moreover, to the highest degree with 

 the production of j?lass for telescopes, microscopes, 

 and such like scientific instruments. This question is 

 of very special importance as regards the construction 

 of instruments for militar\- and naval purposes, in 

 which connection we have hitherto been entirelv de- 

 pendent upon foreign countries. In the previous vear 

 It was proven to the Budget Commission that onlv by a 

 particular accident was it possible to obtain the neces- 

 sary' quantity of glass for the construction of optical 

 instruments essential for the army." 



"The close relationship between the welfare of the 



NO. 2714, VOL. IO8I 



glass-founder and of the optical instrument-maker in 

 the same country," thus forcibly advocated, was 

 already recognised by the Prussian Government, which 

 ■ granted to the Jena undertaking for two years a sum 

 of 60,000 marks." James Weir French. 



Anniesland, Glasgow, October 24. 



The letter published in Nature of October 20 from 

 the Carl Zeiss organisation in Jena through Messrs. 

 J. \V. Atha and Co. is interesting, but not very con- 

 vincing, for Messrs. Zeiss seem to wish to convey a 

 totally dilTerent impression from that of thirty-five 

 years ago. Their present attitude is that although 

 they did receive a small subsidy, a mere 3000L, from 

 the Prussian Government, it was an isolated instance 

 and really quite unnecessary. In view of this the 

 following extract froin the preface to the catalogue 

 of optical glasses issued by Schott and Gen in 1886 

 is interesting: — "We have to express our sincere 

 thanks to the Prussian Bureau of Education and to 

 the Diet of the kingdom for the very liberal and re- 

 peated subsidies by which we were enabled to carry 

 out the costly experiments on a manufacturing scale." 

 The italics in the quotation are mine. 



An analysis of the various optical glasses offered 

 in this 1886 catalogue gives food for thought. Forty- 

 four glasses were offered, of which it was claimed 

 that nineteen were essentially new, and so were 

 printed in heavier tyjje. Fourteen of these were 

 entirely withdrawn from the market within a year 

 or two, as they were absolutely unstable, and were 

 never replaced. Of the remaining glasses five had 

 the following significant remark printed against them, 

 presumably as a recommendation : " Exactly corre- 

 sponds to the hard crown (soft crown, dense flint, 

 etc.) of Chance Bros." Of the remaining glasses it 

 may be said that they were merely slight modifica- 

 tions of the ordinary old-fashioned crowns and flints, 

 having slightlv lower or higher refractive indices than 

 ordinary hard crown, light flint, or dense flint, and 

 a correspondinglv lower or higher dispersion, many 

 of which had been produced by Chance years before. 



Mansell P. Swift. 



Bi Tottenham Court Road, London, W. i, 

 October 2:;. 



In their letter to N.\ture of October 20 (p. 238), 

 Messrs. Zeiss suggest, by implication, that British 

 optical instruments are inferior to those of German 

 manufacture. The following may be of interest : 



I possess three photographic lenses. One a pre-war 

 Goerz, double-anastigmat, 7-in. focal length, working 

 at f/6-8, and two post-war Cooke lenses, one of 85-in. 

 focal length, working at f /4-5, and the other of 15-in. 

 focal length, working at f./5-8. 



All three lenses have recentlv been tested at the 

 National Physical Laboratory. The full reports are 

 too lengthy for publication, but it suffices to quote 

 that the Goerz lens had to be stopped down to f/i6 to 

 give " satisfactory- definition over the entire plate," 

 whereas the Cooke lenses did this at full aperture. 



The Goerz lens, I was informed, was specially 

 selected for me bv Messrs. Goerz 's agency in London, 

 whereas both Cooke lenses were bought from stock 

 at the Army and Navy Stores. 



Possiblv one important factor in the success of the 

 German optical industry- is the skilled way in which 

 their products are advertised. The delusion that they 

 are unequalled is widesoread. K. C. Browning. 



16 Bridge .\venue Mansions, 

 Hammersmith, W.6. 



