JOURNAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



DECEMBER 1902. 



TRANSACTIONS OF THE SOCIETY. 



X. — Electrical Method of Talcing Microscope Measurements. 

 By Philip E. Shaw, B.A., D.Sc. 



(Bead November 19th, 1902.) 



Two years ago * I described a method of taking very small 

 measurements by a new process, that of electric touch. Since then 

 considerable advance has been made on the same lines, and now 

 it is possible to measure one-millionth of a mm. with accuracy, 

 and the method has been used in a variety of physical problems.! 



By simplifying the original instrument a small apparatus, 

 called the Simple Electric Micrometer, has been produced giving 

 measurements of one-thousandth of mm. or less. It has a great 

 number of uses in the physical laboratory, including one applica- 

 tion to the Microscope about to be described. 



This method of measuring is novel in two respects. Firstly, it 

 is electrical ; secondly, it is a direct method, which is in its favour. 



Description. — In the diagram (fig. 126) the essential parts for 

 the measurement are shown. 



The slide si is mounted on the stage s, o being the Microscope 

 objective. A screw sc is brought up to nearly touch the edge of 

 the slide. This screw is carried by a nut n, and has a graduated 

 ■disc cl and milled head m attached to it. If the screw have two 

 threads to a mm., and the graduated disc have 500 divisions, then 

 a movement of the screw-disc by one division corresponds to a 

 movement of the screw-point t by one-thousandth of a mm. (i.e. 

 1 micron). The micrometer-screw is supported on a stand quite 

 separate from the Microscope, so that it can be removed and 

 packed in a separate box for preservation. There is a universal 

 joint j between the screw and the stand, so that we can raise or 

 lower the screw, point it in any direction whatever, and then 

 rigidly clamp it there. Suppose the screw and stage are brought 



* Phil. Mag., Dec. 1900. 



t Phil. Mag., March 1901 ; Electrician, March 1901 and March 1902. 



December 17th, 1902 2 tj 



