January 26, 1905J 



NA TURE 



301 



PROF. ERNST ABBE. 

 Forty Years' Progress, 1866-1905. 

 "pRNST ABBE, born January 23, 1840, was the 

 ■'--' son of a foreman in a spinning mill at 

 Eisenacli. He was a student at Jena and Gottingen, 

 graduating at tfie latter university with a thesis on 

 the mechanical equivalent of heat. After teaching 

 for some time at Frankfort-on-Main, he established 

 himself at Jena in 1863 as a privat decent in mathe- 

 matics, physics, and astronomy, taking for a special 

 subject of instruction the theory of errors. In 1870 

 he was appointed an e.xtraordinary professor. In 

 1874 there was a proposal to establish a physical 

 laboratory at Jena, and Abbe was offered the pro- 

 fessorship of physics, but his connection with Carl 

 Zeiss had then begun, and he was compelled to de- 

 cline the offer. He had married in 1871 the daughter 

 of Prof. Snell, and has left two daughters. 



Carl Zeiss had established himself at Jena in 1846 

 as a manufacturer of optical instruments ; for some 

 years the business prospered, his microscopes were as 

 good as those of other makers, probably neither better 

 nor worse; but Zeiss was not satisfied; he felt that 

 the microscope ought to be improved, and in 

 endeavouring to effect improvement he realised the 

 deficiency of his own equipment ; after one other 

 unsuccessful attempt he enlisted Abbe's help in his 

 work. 



The partnership which has had so remarkable an 

 effect on the manufacture of optical instruments 

 began in 1866. Abbe's task was a hard one; the 

 theory of the microscope was at that date only 

 partially understood ; the corrections to the lenses 

 were made by a rough trial and error method, and 

 the results were doubtful ; the first step was to solve 

 a mathematical problem of no small difficulty, and 

 trace the path of the light through the complex lenses 

 of a microscope objective. 



Abbe soon found out the defects of the ordinary 

 theory, and was led in 1870 to what is now known 

 as the Abbe theory of microscopic vision ; unfortu- 

 nately, no complete account of that theory from his 

 own pen has yet been printed, though the " Collected 

 Papers of Ernst -Abbe," of which the first volume was 

 published last year under the skilful editorship of 

 Dr. Czapski, and noticed in these pages recently 

 (Nature, vol. l.xix. p. 497), go far to fill the gap, 

 and it is to be hoped that Dr. Czapski himself or 

 some other member of the Jena staff will now be in 

 a position to give the complete theory to the world. 

 It is not necessary here to discuss the controversy 

 which has arisen over the matter, due in great 

 measure to an incomplete representation of the 

 problem and to a misconception of the theory. 



It is clear that if we can treat the object as self- 

 luminous, or if we know the distribution of light 

 with respect to both intensity and phase over the 

 object plane, then we may start from the object as 

 our source, and the principles of the wave-theory, as 

 Lord Rayleigh has shown, will allow us to determine 

 ■ the distribution in the view plqne. If, however, the 

 distribution in the object plane is unknown, we 

 must go back to the source, consider how the light 

 from the source is modified both bv the object and 

 the lenses, and from this infer what the resulting 

 image will be like. 



Diffraction patterns will be formed practically in 

 the second focal plane of the object glass, and the 

 distribution of the light in the image can, theo- 

 retically at any rate, be deduced from a knowledge 

 of the intensity and phase of the disturbance in these 

 patterns. 



This theory, at any rate, led .\bbe to most valuable 

 NO. 1839, VOL. 71] 



results, and was one source of the success of the 

 Zeiss microscope. From it, among other conse- 

 quences, lie deduced the importance of what is now 

 known as the numerical aperture, the quantity 

 fi sin a, where fi is the refractive index of the first 

 lens of the object glass, and 2a is the angle which 

 that lens subtends at the point where the axis of the 

 system cuts the object plane. 



But the assistance given by the new theory was 

 not alone sufficient to solve the problem. It had long 

 been known that when the best glasses then obtain- 

 able were combined to form an achromatic system, a 

 secondary spectrum remained, and until this could be 

 removed it was hopeless to look for perfection in the 

 image. 



The experiments of Stokes and Harcourt had been 

 directed to the discovery of glasses free from this 

 defect, and Abbe and Zeiss in their early days made 

 many attempts in the same direction, using in some 

 cases liquid lenses to secure the desired end. 



In 1876 the South Kensington Loan Exhibition of 

 Scientific Apparatus took place, and Abbe came over 

 to inspect it. In his report, published in 1878, he 

 writes : — " The future of the microscope as regards 

 further improvement in its dioptric qualities seems to 

 lie chiefly in the hands of the glass maker," and 

 then he explains in what direction changes are re- 

 quired and how diflicult it is to introduce them. 



This report of Abbe's fell into the hands of Dr. 

 Otto Schott, a glass maker of VVitten, in West- 

 phalia. Schott communicated with Abbe in 1881, and 

 commenced his investigations into the subject. Next 

 year he removed to Jena, and, aided by a large grant 

 from the Prussian Minister of Education, the experi- 

 ments were satisfactorily concluded, and the firm of 

 Schott and Co. was established ; in 1884 he was in a 

 position to commence the wholesale production of 

 optical glass. The combination was now complete. 

 " To-day it is difficult," as Prof. Auerbach writes in 

 his recent work on the Carl Zeiss Stiftung in Jena, 

 " to think of the .Optical Works without the Glass 

 Works, or vice versd." 



From this time onwards Abbe's time was fully 

 occupied in developing the new undertaking ; the 

 history of his life would be the history of the works, 

 and in the Zeiss instruments, known throughout the 

 world, his monument is to be found. 



But in many ways the latter years of his life are 

 not the least interesting. Carl Zeiss died in 1888; 

 next year his son Roderick retired from business, and 

 Abbe was left sole proprietor of the optical works. 

 In 1891 he created a kind of trust known as the Carl 

 Zeiss Stiftung, to which he ceded all his proprietary 

 rights, both in the optical and also in the glass works. 



The story of the Carl Zeiss Stiftung as told by 

 Prof. .Auerbach is a very striking one. The statutes, 

 due to Abbe himself, which were confirmed by the 

 Grand Duke of Saxony in 1896, and have the force 

 of law, can up to 1906 be modified by a simple pro- 

 cedure ; afterwards legal action is practically required 

 to render a change valid. 



The works are a great cooperative concern. " To 

 provide a large number of people with the most 

 favourable opportunities for labour is both the means 

 and the end of the Stiftung. The individuals who 

 benefit by it are at the same time those who main- 

 tain and increase it. The officials and workmen 

 employed at the optical works, the community and 

 the university contribute their share towards the in- 

 crease of the value of the property, and these, there- 

 fore, are entitled to participate in the benefits." The 

 university alone will shortly have received ioo,oooi. 

 from the scheme. 



The Stiftung is managed by the Stiftung .Adminis- 



