66 



NATURE 



[March 27, 19 19 



somewhat limited end in view — namely, the reduc- 

 tion of secondary spectrum — and met with no con- 

 siderable success. 



Fig. 2. — Disc of crown glass, 28 in. in diameer, made by Messrs. Chance 

 Brothers just before the war. 



The English firm and that of Mantois, of Paris, 

 held the field up to about 1880. About this time, 

 owing" to the happy col- 

 laboration between the 

 very distinguished op- 

 tician, Abbe, and the 

 able chemist, Schott, 

 extensive research on 

 the subject of new op- 

 tical glasses was carried 

 out in Germany. 



The advent of dry- 

 plate photography and 

 the special corrections 

 desirable in camera 

 lenses, as well as in 

 microscopic objectives, 

 gave a great stimulus to 

 the work of these in- 

 vestigators, and their 

 researches, carried out 

 with more perfect tech- 

 nical appliances, had a 

 wider aim in view than 

 those of the English ex- 

 perimenters. The results 

 obtained were of such 

 promise and importance 

 that Government assist- 

 ance was forthcoming in 

 ^ the setting up of works 

 for the manufacture of 



new glasses on a commercial scale, and the 

 painstaking efforts of these men of science 

 in overcoming the difficulties involved were 



NO. 2578, VOL. 103] 



eventually rewarded with well-deserved suc- 

 cess. 



As a result, opticians were compelled for many 

 years to ^o to Germany for glasses having special 

 properties such as were absolutely necessary for 

 them in the design of the better types of certain 

 optical instruments. And, as many of the more 

 important instruments during the latter part of 

 last century were of German design, the firms 

 concerned naturally transferred almost the whole 

 of their orders from the English and French firms 

 to Schott and Co., of Jena, and, in fact, so far 

 as the military requirements of Germany were 

 concerned, they were compelled to do so by the 

 German Government. 



It may be said, however, that the products of 

 the English and French firms, as regards the older 

 varieties of optical glass, were never surpassed 

 by the Jena firm. This is evidenced by the fact 

 that the English and French firms produced the 

 great majority of the large discs for the giant 

 astronomical refracting telescopes constructed 

 during the last forty years. At the British Scien- 

 tific Products Exhibition recently held in London 

 and Manchester, a fine disc of crown glass, 28 in. 

 in diameter, which was produced immediately 

 before the war, was exhibited by Messrs. Chance 

 Brothers. 



The British firm, in particular, was slow in 

 taking up the manufacture of the newer types of 

 optical glass, and had to encounter serious dis- 

 advantages in coming late into the field in this 



-The packing and dispatching department of Messrs. Chance Brothers' works, showing a large variety of 

 moulded discs, prisms, etc., required for war purposes. 



respect, as also in being unable to obtain any 

 Government assistance. The great value of the 

 previous production of optical glass in this 



