158 FISCHER: LENGTH STANDARDS AND MEASUREMENTS 



since this country was the first to speciahze in the manufacture 

 of machinery the parts of which are interchangeable. As ex- 

 amples, I need only mention the early manufacturer of watches 

 and sewing machines whose success was absolutely dependent 

 upon the maintenance of one standard throughout their prod- 

 uct. That the manufacturer could not go out in the open mar- 

 ket and purchase the gauges that were needed is shown by a 

 statement of Prof. W. A. Rogers in 1878, who said: 



I have a large collection of micrometers by different makers, both at 

 home and abroad; I have standards by Froment and Brunner of Paris, 

 and Merz of Munich; I have transfers from every well known precision 

 screw in this country, including such makers as Buff and Berger of Bos- 

 ton; Clark of Cambridge; Brown and Sharpe of Providence; Ruther- 

 ford of New York; Clement of London; Bianchi, Froment, and Per- 

 reaux of Paris. The investigation of these transfers is not yet quite 

 completed, but I feel safe in saying that no two of them agree at a given 

 temperature, and the errors of subdivisions are, in many cases, very 

 large, and in all cases easily measurable. Of the micrometers made 

 abroad, the best I have seen are by Powell and Leland. They are 

 superbly ruled, and the errors of the subdivisions are much less than 

 usual, but in the two plates measured, the unit was found to be nearly 

 1| per cent too long. 



While anyone comparing the same class of apparatus at the 

 present time would still find differences, they would be of an 

 entirely different order. 



Even as late as 1880 the very important relation of the yard 

 to the meter as given by different authorities varied from 39.3697 

 to 39.3708 or 0.0011 of an inch. This variation was reduced 

 to a little over two ten-thousandths of an inch at this time by 

 Mr. O. H. Tittman,^ by the apparently simple expedient of 

 referring all the observations to the British Imperial yard and 

 the committee meter at the temperatures at which these bars 

 are standard. 



The United States has been fortunate in having two firms 

 who applied themselves to the task of supplying accurate tools 

 and gauges at the time when American industries began to 

 demand them. I refer to the firms of Brown and Sharpe of 

 Providence, R. I., and Pratt and Whitney of Hartford, Conn., 



^ Appendix No. 16, Coast and Geodetic Survey for 1890. 



