2 SMITHSONIAN METEOROLOGICAL TABLES 



In the case of the pound, this comparison resulted in the conversion: 

 1 pound = 453.59234 grams 



Industrial usage.— In recent years improved industrial techniques have 

 made it desirable to standardize the relationships used by the various English- 

 speaking countries. The conversion 1 inch = 2.54 centimeters has been sug- 

 gested as the best compromise, with the practical advantage of facilitating 

 mechanical conversion between the two systems by means, for example, of a 

 127-tooth gear wheel on a lathe or measuring instrument. The above relation- 

 ship has been the standard for American and British industrial use for several 

 years and has been adopted by both the American Standards Association 5 

 and the British Standards Institution. 6 



Even less practical difference exists between the various definitions of the 

 pound, but the conversion 1 pound = 453.5923 grams has been urged, since 

 this figure is divisible by 7000, the number of grains in a pound. 



At this writing a bill to legalize these two conversions has been prepared 

 for introduction in Congress and the British are expected to legally sanction 

 them by an Order in Council upon enactment of the bill into law. Australia 

 has already adopted the new conversion factors. 



Accordingly, all conversions between the English and metric systems 

 in this volume are based on the relationships: 



1 inch = 2.54 centimeters 

 1 pound = 453.5923 grams 



Nautical mile. — Originally and practically for uses at sea, the nautical 

 mile was considered to be the length of 1 minute of arc on the earth's surface 

 for the given latitude and in the given azimuth on a representative spheroid. A 

 more precise definition is desirable and in the tables issued by the U. S. Office 

 of Standard Weights and Measures, September 1898, the nautical mile is 

 defined as a minute of arc of a great circle on a sphere whose surface equals 

 that of the Clarke spheroid of 1866. The value now given for the nautical 

 mile by the National Bureau of Standards 7 is 1853.248 meters. Using 

 Clarke's ratio of the foot to the meter this length is 6080.27 feet, the value 

 given in Bowditch ; 8 using the ratio annexed to the Act of 1866 this length 

 is 6080.20 feet, the value given in previous editions of these tables. The 

 adoption of the new ratio of the foot to the meter (1 foot = 0.3048 meter) 



8 American Standards Association Report B 48.1, "Inch-Millimeter Conversion for 

 Industrial Use," 1933. 



6 British Standards Institution Report B. S. 350, "Conversion Factors and Tables," 1944. 



7 U. S. Nat. Bur. Stand. Misc. Publ. M 121, 1936. 



8 Bowditch, N., American Practical Navigator, 1938 rev. ed., pp. 20 and 327. U. S. 

 Navy Hydrographic Office, Washington, 1939. On page 144 the factor 6080.20 is given. 



