IxXX INTRODUCTION. 



Table 101. Relative illuminatioii intensities. table 101. 



The table gives illumination intensities in foot-candles for zenithal sun, sky 

 at sunset, sky at end of civil twilight, zenithal full moon, quarter moon, and 

 starlight, and the ratio of these intensities to the illumination ,f rom the zenithal 

 full moon. For the sources of the data see Kimball, Herbert H., " Duration 

 and Intensity of Twilight," Monthly Weather Review, 1916, 44: 614-620. 



MISCELLANEOUS TABLES. 



WEIGHT IN GRAMS OF A CUBIC CENTIMETER OF AIR. 



The following tables (102 to 107) give the factors for computing the 

 weight of a cubic centimeter of air at different temperatures, humidities 

 and pressures. 



o.ooi 2930 ( B — 0.378 e \ 

 )7 1 V 760 / 



8 = 



I + 0.00367 t \ /( 

 in which 8 is the weight of a cubic centimeter of air expressed in grams, 

 under the standard value of gravity ((7 = 980.665) 

 B is the atmospheric pressure in millimeters, under standard grav- 

 ity ; 

 e is the pressure of aqueous vapor in millimeters, under standard 



gravity ; 

 t is the temperature in Centigrade degrees. 

 For dry atmospheric air (containing 0.0004 of its weight of carbonic 

 acid) at a pressure of 760 mm. and temperature 0° C, the absolute density, 

 or the weight of one cubic centimeter, is 0.0012930 gram. See p. xlvi. 

 The weight of a cubic centimeter may also be written as follows : 



g_ 0.0012930 / 7^-0.378 g \ 



I -1-0.002039(^ — 32°) \ 29.921 / 

 where 8 is defined as before, but B and e are expressed in inches and / in 

 Fahrenheit degrees. Thus by the use of tables based on these two formulae, 

 lines of equal atmospheric density may be drawn for the whole world, no 

 matter whether the original observations are in English or metric measures. 



ENGLISH MEASURES. TABLES 102, 103, 104. 



Table 1 02. Temperature Term. 



This table gives the values and logarithms of the expression 

 _ 0.0012930 



^ 29.921 J ^ 0.002039 {t-T,2°) 



for values of t extending from —45° F. to -1-140° F., the intervals between 

 0° F. and 110° F. being 1°. 



The tabular values are given to five significant figures. 



