354 



Table 384 



REDUCTION OF WAVE-LENGTH MEASURES TO STANDARD CONDITIONS 



The international wave-length standards are measured in dry air at 15 C, 76 cm pressure. Density variations ot 

 the air appreciably affect the absolute wave-lengths when obtained at other temperatures and pressures. The follow- 

 ing tables give the corrections for reducing measures to standard conditions, viz.: 5 = Xo(tto — no') {d — do) /do in 

 ten-thousandths of an Angstrom, when the temperature /" C, the pressure B in cm of Hg, and the wave-length X in 

 Angstroms are given ; n and d are the indices of refraction and densities, respectively; the subscript refers to standard 

 conditions . none, to the observed; the prime ' to the standard wave-length, none, to the new wave-length. The tables 

 were constructed for the correction of wave-length measures in terms of the fundamental standard 6438. 46g6 A of the 

 cadmium red radiation in dry air, 15° C, 76 cm pressure. The density factor is, therefore, zero for 15 C and 

 76 cm, and the correction always zero for X = 6438 A. As an example, tind the correction required for X when meas- 

 ured as 3000.0000 A in air at 25 C and 72 cm. Section (a) of table gives (d — do)/do = —.085 and for this value of 

 the density factor section (b) gives the correction to X of —.0038 A. Again, if X, under the same atmospheric condi- 

 tions, is measured as S000.0000 A in terms of a standard X' of wave-length 4000.000 A, say. the measurement will 

 require a correction of (0.0020 + 0.0008) = +.002S A. Taken from Meggers and Peters, Bulletin Bureau of Stand- 

 ards, 14, p. 72S, IQl8. 



(a). — 1000 x {d -do) /do 



(&). — 5 = Xo(no-n ') (d- do) /do, in Ten-thousandth Angstroms 



Smithsonian Tables. 



