24 BULLETIN OF THE 



ard micrometer to the Superintendent of the Coast Survey at 

 Washington, with the request that he will have it compared with 

 a recognized standard in the Bureau of Weights and Measures, 

 and return it with a report of the error, if any. I have reason 

 to believe that such requests would be promptly and courteously 

 responded to. Each society should then preserve the standard 

 thus obtained for the sole purpose of enabling its members to 

 compare their stage-micrometers with it. I think this plan much 

 wiser than to relegate the question to any one of the ingenious 

 men who are endeavoring in this country, with considerable suc- 

 cess, to make accurate rulings on glass, and I should anticipate 

 better results from it than from the appointment of a special 

 committee of the American Society of Microscopists to prepare 

 a standard scale. 



In conclusion, I readily admit that so long as the English 

 microscopists continue to express the results of their measure- 

 ments in decimals of an English inch, there will be American 

 microscopists who will do the same, either for all purposes or for 

 particular work, and of course it is very desirable that these 

 measurements also should be accurate. The stage-micrometers- 

 on this system in the market are usually ruled in hundredths and 

 thousandths of an inch. The latter divisions are too wide to- 

 give values to the eyepiece-micrometer with the higher powers,, 

 while the five-thousandths, ten-thousandths, or even finer divisions,, 

 ruled also on some of these micrometers, are inconveniently close. 

 I would advise the makers to rule such micrometers four-tenths- 

 of an inch long, divided into hundredths of an inch, one of the 

 hundredths being subdivided into ten, another into twenty-five 

 spaces. These latter spaces, each representing one twenty-five- 

 hundredth of an inch, sufficiently approximate the hundredth of 

 a millimetre to be used with equal convenience with the higher 

 powers. The scale on the glass eyepiece-micrometer, used with 

 these stage-micrometers, should be, if specially made for the 

 purpose, four-tenths of an inch long, divided into one hundred 

 parts, each one two-hundred-and-fiftieth of an inch ; but these 

 divisions would so closely approximate those of the metric eye- 

 piece-micrometer proposed, that it might be used without incon- 

 venience instead. Where it is thought worth while by a micro- 

 scopical society to procui*e a standard scale of this kind, it should 

 be sent to the Coast Survey office for measurement, as in the^ 

 case of the metric scales. 



