MICROSCOPE AND ACCESSORIES 



CH. /] 



\ 53. Standard Size Oculars. The Royal Microscopical Society of Lon- 

 don took a very important step (Dec. 20, 1899) in establishing standard sizes 

 for oculars and sub-stage condensers. To quote from the Journal of the Royal 

 Microscopical Society for 1900, p. 147 : 



Resolved, " That the standard size for the inside diameter of the substage 



FIG. 39. Ocular Screw-Micrometer 

 with compensation ocular 6. The upper 

 figure shows a sectional view of the ocular 

 and the screw for moving the micrometer 

 at the right. At the left is shown a clamp- 

 ing sciew to fasten the ocular to the upper 

 part of the microscope tube. Below is a 

 face view, showing the graduation on the 

 wheel. An ocular micrometer like this is 

 in general like the cob-web micrometer 

 and may be used for measuring objects of 

 varying sizes very accurately. With the 

 ordinary ocular micrometer very small 

 obfects frequently fill but a part of an in- 

 terval of the micrometer, but with this 

 the movable cross lines traverse the object 

 (or rather its real image) regardless of 

 the minuteness of the object. (Zeiss } Cat- 

 alog.} See also Ch. IV. 



fitting be 1.527 in. = 38. 786 mm. That the gauges for standardizing eye-pieces 

 be the internal diameters of the draw-tubes, the tightness of the fit being left 

 to the discretion of the manufacturers." 



The sizes for oculars are four in number, i and 2 being most common. 



(1) 0.9173 inch=23. 300 rum. 



(2) 1.04 inch=s6.4i6 mm. 



(3) 1.27 inch.~32.25S mm. 



(4) 1.41 inch 35.814 mm. 



This is the Continental size. 

 This is the size used by the English opti- 

 cians for student and small microscopes. 

 Medium size binoculars (English). 

 Long tube binoculars. 



For the history of the Huygenian Ocular, and a discussion of formulae 

 for its construction, see Nelson, J. R. M. S. , 1900, p. 162-169. 



54. Putting an Objective in Position and Removing it. 

 Elevate the tube of the microscope by means of the coarse adjust- 

 ment, (frontispiece) so that there may be plenty of room between 

 its lower end and the stage. Grasp the objective lightly near its 

 lower end with two fingers of the left hand, and hold it against the 

 nut at the lower end of the tube or the revolving nose piece. 



