76 LIGHTING AND FOCUSIXG [ CH. II 



for the best laboratory microscopes. The mechanical work also is of excel- 

 lent quality. 



During the last few years great vigor has been shown in the microscopical 

 world. This has been stimulated largely by the activity in biological science 

 and the widespread appreciation of the microscope, not only as a desirable, 

 but as a necessary instrument for study and research. The production of the 

 new kinds of glass, (Jena glass), and the apochromatic objectives has been a 

 no less potent factor in promoting progress. The student is advised to write 

 to one or more of the opticians for complete catalogs. (See list, p. 2 of cover) . 



STANDARD SIZES RECOMMENED BY THE ROYAL 

 MICROSCOPICAL SOCIETY 



$ 135. Society Screw. Owing to the lack of uniformity in screws for 

 microscope objectives, the Royal Microscopical Society of London, in 1857, 

 made an earnest effort to introduce a standard size. 



In order to facilitate the introduction of this universal screw, or as it soon 

 came to be called " The Society Screw,'" the Royal Microscopical Society under- 

 took to supply standard taps. From the mechanical difficulty in making these 

 taps perfect there soon came to be considerable difference in the "Society 

 Screws," and the object of the society in providing a universal screw was 

 partly defeated. (See Edward Bausch, Trans. Amer. Micr. Soc., 1884, p. 153.) 



In 1884 the American Microscopical Society appointed Mr. Edward Bausch 

 and Prof. William A. Rogers upon a committee to correspond with the Roya] 

 Microscopical Society, with a view to perfecting the standard " Society Screw," 

 or of adopting another standard and of perfecting methods by which the screws 

 of all makers might be truly uniform. Although this matter was earnestly 

 considered at the time by the Royal Microscopical Society, the mechanical 

 difficulties were so great that the improvements were abandoned. 



Fortunately, however, during the year 1896 that society again took hold 

 of the matter in earnest, and the " Society Screw" is now accurate, and facili- 

 ties for obtaining the standard are so good that there is a reasonable certainty 

 that the universal screw for microscopic objectives may be realized. It is 

 astonishing to see how widely the " Society Screw has been adopted. Indeed 

 there is not a maker of first-class microscopes in the world who does not supply 

 the objectives and stands with the "Society Screw," and an objective in 

 England or America which does not have this screw should be looked upon 

 with suspicion. That is, it is either old, cheap, or not the product of one of 

 the great opticians. For the Standard, or " Society Screw," see: Trans. Roy. 

 Micr. Soc., 1857, pp. 39-41; 1859, pp. 92-97; 1860, pp. 103-104. (All to be 

 foundin Quar. Jour. Micr. Sci., o. s., vols.VI, VII, VIII). Proc. Amer. Micr. 

 Soc. 1884, p. 274; 1886, p. 199; 1893, p. 38. Journal of the Royal Microscopical 

 Society, August, 1896. 



