374 



Table 41 3 



index of refraction 



TABLE 413. — Index of Refraction of Air (15°C, 76 cm) 



Corrections for reducing wave lengths and frequencies in air (75° C, 76 cm) to vacuo. 



The indices were computed from the Cauchy formula (n — i)io 7 = 2726.43 + I2.288/(A 2 X icr 8 ) +0.3555/ 

 (A 4 X io -16 ). Foro C and 76 cm the constants of the equation become 2875.66, 13.412 and 0.3777 respectively, and 

 for 30° C and 76 cm, 2589.72, 12.259 and 0.2576. Sellmeier's formula for but one absorption band closely fits the 

 observations: n 2 = 1 + 0.0005 73 78X 2 /(X 2 — 595260). If w — 1 were strictly proportional to the density, then (n — 1)0/ 

 in — i)( would equal 1 + at where a should be 0.00367. The following values of a were found to hold: 



X 0.85/x 0.75M 0.65M 0.55M 0.45/U 0.35/11 0.25/i 



a 0.003672 0.003674 0.003678 0.003685 0.003700 0.003738 0.003872 



The indices are for dry air (0.05 ±%CO ;; ). Corrections to reduce to dry air the indices for moist air 

 may be made for any wave-length by Lorenz's formula, + 0.000041 (ra/760), where m is the vapor pres- 

 sure in mm. The corresponding frequencies in waves per cm and the corrections to reduce wave-lengths 

 and frequencies in air at 15 ' C and 76 cm pressure to vacuo are given. E.g., a light wave of 5000 

 Angstroms in dry air at 15° C, 76 cm becomes 5001.391 A in vacuo; a frequency of 20,000 waves per cm 

 correspondingly becomes 19994.44. Meggers and Peters, Bui. Bureau of Standards, 14, p. 731, 1918. 



Smithsonian Tables. 



