CONVERSIONS INVOLVING LINEAR MEASURES. XXI 



here adopted between the meter and the yard, the English measure of 

 length, is i meter = 39.3700 inches, as legalized by Act of U.S. Congress, 

 July 28, 1866. This U.S. Standard of length must be distinguished from the 

 British Imperial yard, comparisons of which with the international proto- 

 type meter give the relation i meter == 39-370II3 inches. (See Smithsonian 

 Physical Tables, 1916, p. 7, Table 3.) 



Table 9. Inches into millimeters. table 9. 



I inch = 25.40005 millimeters. 



The argument is given for every hundredth of an inch up to 32.00 inches, 

 and the tabular values are given to hundredths of a millimeter. A table of 

 proportional parts for thousandths of an inch is added on each page. 



Example : 



To convert 24.362 inches to millimeters. 

 The table gives (p. 20). 



(24.36 + .002) inches = (618.75 + O-OS) mm- "= 618.80 mm. 



Table 10. Millimeters into inches. table 10. 



From O to 400 mm. the argument is given to every millimeter, with 

 subsidiary interpolation tables for tenths and hundredths of a millimeter. 

 The tabular values are given to four decimals. From 400 to looo mm., 

 covering the numerical values which are of frequent use in meteorology 

 for the conversion of barometric readings from the metric to the English 

 barometer, the argument is given for every tenth of a millimeter, and the 

 tabular values to three decimals. 



Example : 



To convert 143.34 mm. to inches. 

 The table gives 



(143 + .3 + .04) mm. = (5.6299 + 0.0118 +0.0016) inches = 5.6433 

 inches. tables 11. 12. 



Tables 11, 12. Conversion of barometric readings into standard units oj 

 pressure. 



The equation for the pressure in millibars, ' P„,i, corresponding to the 

 barometric height, B, is 



1000 



where A is the densitv of mercury and g^ is the standard value of gravity. 



^ The value of the bar as here defined is a pressure of 1,000,000 dynes per square 

 centimeter, and is that employed by meteorological services, and recommended by inter- 



