ABSTRACTS 



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PHYSICS. — A simplified formula for the change in order of interference 

 due to changes in temperature and pressure of air? Irwin G. Priest, 

 Bulletin Bureau of Standards, vol. 9, in Press. 

 The author developed independently for use at the Bureau of Stand- 

 ards the following correction formula : 



\ 1+fi l+at2 J \380X 



where ti = lower temperature Centigrade, tz = higher temperature 

 Centigrade, 61 = pressure in mm. of mercury at temperature ti, 62 = 

 pressure in mm. of mercury at temperature t^, I = distance between 

 mirrors, n = refractive index at 0°, 760 mm., a = coefficient of expan- 

 sion of air, X = wave length. 



He noticed later that the formula published by Pulf rich,^ viz : 



K = l(t,-t,) ^' ^ ^ 



760 !+«<! l+at2 



2(M-l)a 



•^(62- 61) 



l+a^2 



"2(m-1) 

 760X 



could be reduced to this simpler and more convenient form. The 

 derivation of the new formula is given and the two formulas are compared 

 as to convenience in practice. I. G. P. 



^ To understand this abstract the reader must see first Pulfrich. Zeit. fur Inst. 

 K. 13: 456. 



^ The sign in Pulfrich's paper is in error if the expression is to give the correction 

 not the error. 



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