CIV EXPLANATION OF SOURCE AND USE OF TABLES. 



Table 31 gives the mean astronomical refraction in terms of the apparent alti- 

 tude of a star or other object outside the earth's atmosphere. It is taken from 

 Vega's 7-place table of logarithms. Its use will be evident from the following 

 example : — 



Apparent altitude of star = 34° 17' 12. "7 



Refraction = 1' 24. "3 — |, X i-"i = i 24.1 



True altitude of star =34 15 48.6 



Tables 32 and 33 facilitate the interconversion of arc and time. They are 

 taken from the " Smithsonian Meteorological Tables" (the first volume of this 

 series). The following examples illustrate their use : — 



(i.) To convert 68° 29' 48."8 into time we have from Table 32 — 



Equivalent In time = 4 33 59.25 

 (2.) To convert 5'' 43*" 28.^8 into arc we have from Table 33 — 



Equivalent in arc = 85 52 12 



Tables 34 and 35 facilitate the interconversion of mean solar and sidereal 

 time intervals. They are taken from Vega's 7-place table of logarithms. The 

 mode of using them is explained in the tables themselves. 



Tables 36 and 37 give the lengths of degrees of terrestrial arcs of meridians 

 and parallels expressed in metres,* statute miles (English), and geographic miles 

 (distance corresponding to i' on the earth's equator). These tables are taken 

 from the "Smithsonian Meteorological Tables" (the first volume of this series). 



Table 38 facilitates the interconversion of statute (English) miles and nautical 

 miles. The nautical mile used is that defined by the U. S. Coast and Geodetic 

 Survey, namely : the length of a minute of arc of a great circle of the sphere 

 whose surface equals that of the earth (Clarke's spheroid of tS66). For formula 

 for radius of such sphere see p. Hi. This table is taken from the " Smithsonian 

 Meteorological Tables " (the first volume of this series). 



Table 39 gives the English and metric equivalents of other standards of 

 length still in use or obsolescent. It is taken from the " Smithsonian Meteoro- 

 logical Tables " (the first volume of this series). 



Table 40 gives values of the acceleration (g) of gravity, log g, log (1/2^), log ^2 g, 



* It should be observed that the metric values given in these tables depend on Clarke's value 

 of the ratio of the yard to the metre, which is now known to be erroneous by about the i/ioooooth 

 part. 



