April 27, 19 16] 



NATURE 



181 



tion of new kinds of glass that has enabled Abbe to 

 work out the conditions of practical apochromatism. 



In the same volume, p. 848f, Zeiss's catalogue, 

 ' Neue Mikroskop-Objective und Okularen aus Specal- 

 Glazer des Glastenchnischen Laboratoriums " (Schott 

 jnd Gen.), is reproduced "nearly in extenso." The 

 same suggestion that only the new glasses are relied on 

 is present throughout. Thus: "The objectives, how- 

 ever, like all productions of our firm, stand on an 

 absolutely free basis. The glass employed is, by our 

 own instrumentality, accessible to anyone, and no 

 optician is in the least degree prevented from pro- 

 ducing the same objectives as good and as cheap as 

 he can." This is followed by extracts from the 

 hlet by Abbe and Schott describing the new 

 s, with their optical and other properties and 

 inces. The abstractor seems by this time to have some 

 suspicions as to whether scientific candour is not here 

 empered with commercial reticence, for he goes on : — 

 " Suggestions are made as to the glass best suited 

 or various purposes, and on commencing the perusal 

 !>f these passages we had the idea that we were com- 

 ng to a description of the glass used for the new 

 ' bjectives. The following ingeniously worded para- 

 raph, however, closes the subject. 

 ! " In the case of microscopic objectives which re- 

 luire for the attainment of the highest capacity of 

 erformance not only agreement in the course of the 

 ;ispersion of the crown and the flint, but also the 

 |jrrection of the spherical aberration and its chromatic 

 jifference, it must be left to the skill of the practical 

 'Dtician to choose the most suitable means from the 

 ,)ove series. The new objectives of Zeiss show what 

 :in be attained by their practical use." 

 j We now pass to vol. vii., containing (p. 2of) a paper 

 ad before the Royal Microscopical Society on Octo- 

 Ir 13, 1886, entitled "On Improvements in the Micro- 

 lope with the Aid of Ne-ju Kinds of Optical Glass." 

 j3 contents fully justify the title; throughout the same 

 ggestion is made that the glasses are alone respon- 

 )le for enabling the optician to attain the improve- 

 :-nts connoted by the term apochromatism. 



must state that the italics in the cited passages 

 ;il mine.) 

 Three comments will close this somewhat long 

 Iter:— 



Prof. Abbe, of Jena, was the brother-in-law of 

 Zeiss, the "practical optician" of Jena. 

 It was soon discovered that one lens of fluorite 

 jorspar), the native fluoride of calcium, was an 

 nal component of the apochromatic objective, as 

 as certain of the new glasses. 

 Before the new lenses were placed on the market 

 ouse of Zeiss had, as they believed, secured the 

 supply of colourless, flawless fluorite, suitable 

 rjtical purposes, which, like so many minerals, is 

 cted to few localities. Marcus H.artog. 



rk, April 6. 



OF. Hartog, in his " comments " Nos. 2 and 3, 

 :s an old charge which was made by Mr. Lewis 

 -:ht in the English Mechanic (1892), pp. 220-221. 

 Lewis Wright, in speaking of the use of fluorspar 

 e production of apochromatic objectives, there 



! hough some of them have managed to secure a 

 supply, others are painfuUv aware that before 

 se of fluorite was allowed to become public all 

 :nowTi available material had been secured bv the 

 of Zeiss at Jena ; and the difficultv of getting 

 lal experienced by some of our best' makers is a 

 oable obstacle to optical improvements and tends 

 ;ihcially keep up the prices." 



. .,, '? .*^^5?^ ^'^s replied to and repudiated by Dr. 



v^jski, in a letter whirh appeared in the same 

 NO. ^Aoft •\rnT r^Tl 



volume of the English Mechanic, p. 287. Dr. Czapski 

 in this letter states : — 



"As regards fluorspar, Mr. Lewis Wright is labour- 

 ing under a great delusion in assuming that before 

 the use of fluorite was allowed to becojne public, all 

 the known available material had been secured by the 

 firm of Zeiss at Jena. The contrary may be said with 

 more truth. The firm of Zeiss possessed but a very 

 scanty supply at a time when, even previous to Mr. 

 Koristka's groundless attacks in the Journal de Micro- 

 graphie, the fact that fluorspar was being used in the 

 apochromatic lenses had been published three times in 

 consequence of information supplied by the firm of 

 Zeiss. 



" The latter were completely prepared to produce 

 their future apochromatic lenses without having re- 

 course to fluorspar, which by no means constitutes the 

 condition sine qua non for the production of apo- 

 chromatic objectives, excepting, of course, in the case 

 of such opticians who can only produce them by 

 slavishly copying existing systems. As, however, the 

 firm became eventually possessed of a considerable 

 quantity of clear material, the employment of fluorite 

 in their apochromatic lenses was continued." 



The letters referred to above are reproduced in the 

 Journal of the Royal Microscopical Society for 1892, 

 pp. 552-555, from which the above quotations are taken. 



I may be allowed to add that if Prof. Abbe and the 

 firm of Carl Zeiss had wished to play the "dog-in-the- 

 manger," they could easily have done so by taking 

 out a patent for the application of the principle of 

 apochromatic construction to microscope objectives. 

 Prof. Abbe's "ethics," however, would not permit of 

 this being done. He, I believe, held that since micro- 

 scope objectives were practically entirely used for the 

 purposes of scientific research, the taking out of a 

 patent for them would have acted prejudicially to the 

 best interests of science in general. 



F. J. Cheshire. 



The Remarkable Meteors of February 9, 1913. 



The large meteors which passed over Northern 

 America on February 9, 1913, presented some unique 

 features. The length of their observed flight was 

 about 2600 miles, and they must have been moving in 

 paths concentric, or nearly concentric, with the earth's 

 surface, so that they temporarily formed new terres- 

 trial satellites. Their height was about 42 miles, and 

 in the Journal of the R.A.S. of Canada there are 

 70 pages occupied with the observations and deduc- 

 tions made from them by Prof. C. A. Chant. 



The meteors were last seen from the Bermuda 

 Islands, according to the descriptions in the journal 

 named (May-June, 1913). 



I have since made efforts to obtain further observa- 

 tions from seafaring men through the medium of the 

 Nautical Magazine, and have succeeded in procuring 

 data which prove that the meteors were obser\'ed 

 during a course of 5500 miles from about lat. 51° N., 

 long. 107° W., to lat. 5i° S., long. 32^° W. 



Mr. W. W. Waddell, first mate of the s.s. Newlands, 

 writes me that at 12.13 P-™-, February 9, 1913, he 

 saw a brilliant stream of meteors passing from the 

 N.W. to the S.E. during a period of six minutes. 

 The ship was in lat. 3° 20' S. and long. 32° 30' W. at 

 the time. He says the meteors disappeared in the 

 region of Argo to the south, and I have assumed thev 

 were over about lat. 5^° S. and long. 32^° W. when 

 he lost sight of them. 



Such an extended trajectory is without parallel in 

 this branch of astronomy. Further reports from 

 navigators in the South Atlantic Ocean might show 

 that the observed flight was even erreater than 5500 

 miles. \v. F. Denning. 



44 Egerton Road, Bristol. 



