164 ANIS^AL REPORT SMITHSONIAN INSTITUTION, 1940 



that the inch and the pound should be fixed in terms of the meter 

 and the kilogram, respectively, by means of specified ratios. The 

 ratio proposed for the inch was 



1 inch =0.0254 meter. 



The bill also carried a supplementary definition of the inch in 

 terms of light waves. This was based upon the value adopted by 

 the International Committee on Weights and Measures for the num- 

 ber of wave lengths of the red radiation of cadmium in a meter, a 

 value which, as I shall show later, is well supported by several inde- 

 pendent determinations. 



This bill did not come to a vote. Hearings were held by the 

 Committee on Coinage, Weights, and Measures, and the provisions 

 of the bill were found to meet with the general approval of industry. 

 In fact some men directly concerned with precise industrial measure- 

 ments were inclined to urge that the inch be defined directly in terms 

 of the wave length of the red radiation of cadmium. It se^ms de- 

 sirable, however, to have the inch, like the centimeter, based upon 

 an actual material standard. And it is important that this standard 

 should be common to the two systems of units in order that the ratio 

 of the two units of length may be unequivocally fixed. 



Opposition to the bill came from an unexpected quarter. The 

 system of plane coordinates which forms the basis for Federal and 

 State surveys is in terms of English units. Now the primary tri- 

 angulation sur\^eys of the United States Coast and Geodetic Survey 

 are all carried out in the metric system, and in converting these 

 measurements to plane coordinates in feet, the ratio 1 meter = 

 3937/1200 feet has been used. Those engaged in these mapping 

 operations naturally do not wish to see this procedure changed, and 

 with this viewpoint the National Bureau of Standards is in complete 

 sympathy. An amendment to the original bill has therefore been 

 proposed, authorizing the continued use of the adopted ratio in the 

 conversion of metric geodetic measurements to English miits in con- 

 nection with plane coordinates, elevations, and other map data. 

 This amendment provides full authority to maintain the present 

 procedure in geodetic conversions without sacrificing all the other 

 desirable provisions of the bill. It should be emphasized that the 

 point involved relates only to a computation, namely the conversion 

 into feet of measurements originally carried out in meters in making 

 primary surveys. A change of two parts in a million in the basic 

 value of the inch would not have any eflFect whatsoever upon any 

 surveys made directly in feet because such surveys camiot approach 

 this order of accuracy. As a matter of fact the hundred-foot tapes 

 calibrated by the National Bureau of Standards are certified to only 

 1 part in 100,000. 



