STANDARDS OF MEASUREMENT — BRIGGS 163 



from the fact that the meter is given as equivalent to 39.37 inches, 

 while the millimeter is rounded off to 0.0394 inch. 



The platinum-iridium meter and kilogram, supplied to our Gov- 

 ernment as a result of its participation in the Metric Convention, 

 provided this country with far better material standards than it had 

 ever had before. Both the meter bar and the kilogram had been 

 carefully compared with the international prototypes, and the co- 

 efficient of expansion of the meter bar had been measured. More- 

 over, they constituted, together with the Troy pound, the only legal 

 material standards possessed by the Government. Accordingly, in 

 the absence of further congressional action. Superintendent Menden- 

 hall of the Coast and Geodetic Survey in 1893 issued the following 

 order : 



The Office of Weights and Measures with the approval of the Secretary of the 

 Treasury, will in the future regard the international prototype meter and kilo- 

 gram as fundamental sfeindards, and the customary units, the yard and the 

 pound, will be derived therefrom in accordance with the act of July 28, 1866. 



It will be recalled that the act of 1866 defines the meter in terms 

 of the inch, and when this is transposed by the Mendenhall order 

 it leads to the incommensurate relation 



1 inch=0.02540005 + meter. 



It is obvious that it is not practicable to lay off this incommensurable 

 decimal fraction on a meter bar, so that this relation defines a theo- 

 retical inch rather than one that can be derived with exactness from 

 the meter bar. The inch thus defined is also about four-millionths 

 longer than the British inch, which is determined directly from the 

 Imperial yard. 



As a matter of fact, the inch now used for engineering purposes 

 both in the United States and Great Britain, and in 13 other coun- 

 tries as well, is based upon the simpler relation, 1 inch equals 25.4 

 millimeters exactly. From this simplified relation it is practicable 

 to derive the inch from the meter bar. Furthermore, it is possible 

 to shift from English to metric units on a screw-cutting lathe by the 

 introduction of a gear having 127 teeth. Finally the ratio 25.4 falls 

 midway between the present accepted values of the British and the 

 United States inch. Both countries could adopt this value without 

 disturbing industry in the slightest, because a change of two parts 

 in a million would not be detected in any industrial operation. 



To summarize the situation, the United States for 150 years has 

 been using a customary system of weights and measures without 

 "fixing" the standards on which the S3^stem is based. A bill was 

 presented to the last Congress with the simple objective of putting 

 tlie Govenmient's house in order in this respect. The bill provided 



280256—41 12 



