62 LABORATORY MICROSCOPES. [CM. IT. 



in removing the thin plate and instead, having a clamp to catch the ends of the 

 glass slide. The slide is then moved on the face of the stage proper. This modi- 

 fication was first made by Mayall. It has since been modified by Reichert, Zeiss, 

 Leitz and others in Europe and by the Bausch & Lomb Optical Co. in America. — 

 (Jour. Roy. Micr, Soc, 1SS5, p. 122. See also Zeit. wiss. Mikroskopie, (II), 18S5, 

 pp. 289-295 ; 18S7, (IV,, pp. 25-30). 



\ 117. Society Screw. — Owing to the lack of uniformity in screws for microscopic 

 objectives, the Royal Microscopical Society of London, in 1857, made an earnest 

 effort to introduce a standard size. The specifications of this standard are as fol- 

 lows : " Whitworth thread, i e., a V shaped thread, sides of thread inclined to an 

 angle of 55 to each other, one-sixth of the V depth of the thread being rounded off 

 at the top of the thread, and one-sixth of the thread being rounded off at 

 the bottom of the thread. Pitch of screw, 36 to the inch ; length of thread on 

 object-glass, 0.125 inch ; plain fitting above thread of object glass, o 15 inch long, 

 to be about the size of the bottom of male thread ; length of thread of nose-piece 

 [on the lower end of the tube of the microscope], not less than o 125 inch ; diam- 

 eter of the object-glass screw at the bottom of the screw, o 7626 inch ; diameter 

 of the nose piece screw at the bottom of the thread, o 8 inch. 



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 undertook to 

 supply standard taps. From the mechanical difficulty in making these taps per- 

 fect 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. 



In 1884 the American Microscopical Society appointed Mr. Edward Bausch and 

 Prof. William A Rogers upon a committee to correspond with the Royal Micro- 

 scopical 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 present year (1896) that society has again 

 taken hold of the matter in earnest, and we are now promised a new "Society 

 Screw" which shall be accurate ; and facilities for obtaining the standard will be 

 so good that there is a reasonable certainty that the universal screw for micro- 

 scopic objectives may be realized. It is indeed astonishing to see how widely 

 spread the " Society Screw " has become. 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, 1S57, pp. 39-41 ; 1859, pp. 92-97 ; i860, pp. 

 103-104. (All to be found in Quar. Jour. Micr. Sci., o. s., vols. VI, VII and VIII). 

 Proc. Amer. Micr. Soc, 1884, p. 274; 1886, p. 199; 1893, p. 38. Journal of the 

 Royal Microscopical Society, Aug., 1896. 



In this last paper of four pages the matter is very carefully gone over and full 

 specifications of the new screw given. It conforms almost exactly with the orig- 

 inal standard adopted by the society, but means have been devised by which it may 

 be kept standard. 



