320 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



to depend on the weather, the spectrometer measurements were always 

 made by means of the five bright lines, Ka, Ha, Na, H^s, Hy, after the 

 methods described in Prof. Abbe's paper, ' Neue Apparate,' &c. 



There were innumerable difficulties to be overcome in order to 

 obtain compositions which should not only show the optical properties 

 desired, but at the same time fulfil so many other requirements for 

 optical glass ; and many repeated trials were necessary for one and 

 the same subject before a satisfactory result could be obtained. It is 

 due to the ingenuity and energy of Dr. Schott that these obstacles 

 were overcome. 



Towards the end of 1883, Prof. Abbe and Dr. Schott had exhausted 

 the programme, as far as appeared possible in a laboratory-research, 

 and were about to close the afi"air, and publish the results, as showing 

 the possibility of a series of new kinds of optical glass, and thereby 

 giving an impulse, as was hoped, to its manufacture. At this period, 

 however, several distinguished astronomers and physicists who had 

 taken notice of these researches, encouraged them to go one step 

 further, and to undertake the practical utilization of the results in the 

 way of manufacture. Through the aid of these gentlemen a subsidy 

 was obtained from the Prussian Government (though Jena is not in 

 Prussia) to continue the experiments, so as to establish a manufacture 

 of optical glass, which did not exist in Germany. Messrs. Zeiss, 

 who had already furthered the work, since the beginning, in the 

 most liberal manner by putting all the personal and technical 

 resources of their establishment at Prof. Abbe and Dr. Schott's 

 disposal, united with them, and in the beginning of 1884 glass-works 

 were set up, with a large furnace and machinery. The Prussian 

 Government's subsidy was 3000Z., and given under conditions as 

 liberal as any Government has ever granted when putting public 

 money into the hands of private persons. 



The new furnace was lighted in September 1884, and since that 

 time Dr. Schott has been actively engaged, almost day and night, in 

 overcoming the difficulties of the operations. The experiences of 

 other manufacturers being inaccessible to a new competitor, every- 

 thing had to be learned anew. A year later, the first part of the 

 matter was brought to an end — the production of the ordinary 

 siliceous glass, and this, since last autumn, is used by nearly all 

 German opticians. In a few months, it is hoped, that the borates and 

 the phosphates will also admit of regular production, and then the 

 Jena manufactory will be opened for the supply of optical glass on a 

 strictly scientific basis. 



This extension of the work has had the effect of delaying the 

 introduction of better glass into microscopical optics by more than 

 two years. In the eummer of 1883, sufficient materials had been 

 obtained for the construction of microscope-lenses, and, in fact, the 

 first objectives were made by Messrs. Zeiss at that period, but after 

 it had been decided to establish a manufactory with the aid of public 

 money, Messrs. Zeiss were obliged to abstain from using the new 

 glass, and to wait until the latter should be accessible to other 

 opticians also. 



