1 6 Transactions. 



standard was possible, by which all micrometers that are to be recognized as cor- 

 rect must be verified. Prof. Phin discussed the subject of fine ruling, and stated 

 that the difficulty in making micrometers was not in securing accuracy of spacing, 

 but in determining the true value of the divisions of the unit. He opposed the 

 acceptation, on the part of the society, of any standard until it had been properly 

 verified by a proper body appointed by the society for that purpose, and said that 

 at present we have only the statement of one man — Prof. Rogers, the maker, that 

 the divisions of the proposed standard were true fractions of the unit. He main- 

 tained that the society should not sanction any standard until its accuracy had 

 been verified by members from independent observations from the U. S. 

 standards. 



The Secretary maintained that while the gentleman was entirely right in saying 

 that the society should not adopt a standard without assuring itself as to its accu- 

 racy, the proposed method of doing so was quite impracticable. He thought 

 there was no member of the society sufficiently experienced in making minute 

 measurements, or familiar with the means of dividing up a given space, to justify 

 any such attempt on our part. Prof. Rogers had worked for years before he suc- 

 ceeded in accomplishing the result, and as he is a recognized authority in this 

 matter, and a thoroughly scientific man, his results are entitled to our considera- 

 tion. 



Nevertheless it becomes us to verify his results by the examination of his 

 methods and instruments, as suggested by Mr. Whitehead, and this would properly 

 be the duty of the delegates from the five societies. After all it is not so much 

 the exact i-iooo of an inch or i-ioo of a mm. that we need, as it is a certain value 

 of the divisions which we can adopt as our standard, and which shall be so nearly 

 the exact division of our assumed unit as to be practically true. The resolutions 

 of the Congress allowed a variation of 1-75000 of an inch in the standard 

 measures. 



Mr. Phin replied that this course would be establishing a new value for the 

 millimeter or unit. 



Mr. C F. Cox said that he could not agree wdih Mr. Whitehead that only one 

 standard micrometer should be recognized, because absolute accuracy was impos- 

 sible, and five or more could be made practically alike. 



The five micrometers might be compared, and the average value of the divisions 

 taken as the standard. The variation of each one from this average could then be 

 stated. He thought the i-loo mm. unit was too small. 



Mr. Haswell drew attention to the new standard measure of Capt. Clark, which 

 he thought would be adopted universally before long. 



After some further discussion, the Board of Managers was instructed to report a 

 plan for action as soon as it could be matured. 



The difficulties in the way of carrying out the resolutions of the Congress are 

 foreseen, but the members are in favor of giving careful attention to the subject, 

 and will not shirk the responsibilities involved. 



The Secretary then read a paper on "Oblique Illumination." 



The President announced that Mr. Scott would be at the room on Monday and 

 Wednesday evenings, to meet such members as desired instruction in mounting 

 and preparing objects 



A letter was read, addressed to the President, asking him to attend a meeting to 

 be held m this City, October 9th, to discuss needed alterations in the postal laws. 



The President was made a delegate from the Society, to attend this meeting, and 

 the Secretary a substitute in case he could not attend. 



After adjournment, the Secretary exhibited a specimen of the alga Merismtpedia 

 com'jtlvati, found at Port Morris, N. Y. 



