22 BULLETIN OF THE 



Mr. J. J. Woodward made the following communication 



ON A STANDARD FOR MICROMETRY. 



Mr. Woodward read a letter he had recently received from a 

 committee of the microscopical section of the Troy Scientific 

 Association, asking answers to the following questions !« — 



" 1, Is it expedient at present to adopt a standard for microm- 

 etry? 



2. If so, should the English or the metric system be employed? 



3. What unit, within the system selected, is most eligible? 



4. What steps should be taken to obtain a suitable standard 

 measure of this unit ? 



5. How can this standard micrometer be best preserved and 

 made useful to all parties concerned?" 



These questions were asked with a view to some action to be 

 taken on the subject at the meeting of the American Society of 

 Microscopists to be held in Buffalo during the summer of 18Y9. 

 He had made the following reply, with regard to which he invited 

 comments or criticism by the Society. 



I submit the following replies to the questions of your circular 

 letter of December 2d: — 



1. I am in favor of the adoption of a suitable standard for 

 micrometry by the American Society of Microscopists at their 

 next meeting. 



2. For this particular purpose I think the metric system offers 

 so many conveniences that I favor its employment. 



3. The selection of an eligible unit within the system involves, 

 it appears to me, two distinct questions : A. How shall the stage- 

 micrometer be ruled ? B. How shall the measurements made be 

 expressed in speech or writing ? 



A. The object of the stage-micrometer is chiefly to give values 

 to the divisions of the eyepiece-micrometer with the power used 

 in any given case. It should be long enough to be used for this 

 purpose with the lowest powers of the compound microscope, and 

 have a part of its length ruled sufficiently close to answer the 

 same end with the highest powers. I favor the adoption of a 

 standard scale a centimetre long ruled in millimetres, and one 

 of these ruled in hundredths. I have used stage-micrometers 

 ruled in thousandths of a millimetre, but regard such divisions 

 as inconveniently close for this purpose. To measure in thou- 



