Table 40 (continued) 85 



PROBABLE VALUES OF THE GENERAL PHYSICAL CONSTANTS 



Note. — It is evident that the definition of the normal atmosphere given by 

 Dorsey in the I.C.T. is technically quite different from Henning and Jaeger's 

 in the H.P. The I.C.T. definition makes the normal atmosphere a conventional 

 constant, with no probable error. Doctor Birge had some correspondence on 

 this matter with Doctor Dorsey, leading to the conclusion that the H.P. defini- 

 tion is correct. The adopted value is therefore based on this H.P. definition. 



Unfortunately, an article by Burgess * was overlooked in which the "standard 

 atmosphere " is defined as " the pressure due to a column of mercury 760 mm 

 high, having a mass of 13.5951 g • cm" 3 , gravitational acceleration of 980.665 

 cm • sec." 1 , and is equal to 1,013,250 dyne • cm -2 ." It is thus a conventional 

 constant, with no error. This definition was adopted in 1927 by the Inter- 

 national Commission of Weights and Measures. Fortunately, this definition 

 makes no change in the magnitude or the error of any derived constant. It 

 should be noted that no temperature is specified and that the word " mercury " 

 is technically superfluous. This seems very objectionable, since there is thus 

 technically no simple method for reducing to standard atmospheres an actual 

 barometer reading at an actual observed temperature. The H.P. definition, 

 as used by Doctor Birge, seems preferable, in spite of international agreement. 



The absolute temperature of the ice-point (T ). — The generally accepted 

 value of T was, for many years, 273.09°K., based on Berthelot's analysis* of 

 the data of Chappuis, 3 and of Joule and Thomson for the porous plug experi- 

 ment. The final average value was y = 36618 X io~ 7 , or T = 273.O9 o . The 

 I.C.T. gives !T = 273.1 as one of its basic constants. 



Most extensive observations on the volume and pressure coefficients (a and 

 /?) of certain gases have recently been made by Henning and Heuse, 4 at the 

 Reichsanstalt. The value of y was obtained by two different methods. 5 



The first method gave for the gases He, H 2 , and N 2 , y X io 7 = 36600, 36607, 

 and 36606, or 7^ = 273.224°, 273.172 and 273.179 . The mean is yXio 8 

 = 366043 or 70 = 273.190° ±0.015. 



The second method gave for He (two determinations at slightly different 

 p ), H 2 and N 2 , 7Xio 7 = 36598, 36597, 36617, and 36604. The mean is 

 36604.0 or T = 273.194°. They conclude that the best mean value of all the 

 experiments is yXio 7 = 366o4. The reciprocal of this is 7^ = 273. 19°. They 

 write it as 273.20°. In the later article 4 by Heuse, neon is used, and the above 

 value of y is confirmed. 



The only other determination of T of comparable accuracy is that by 

 Roebuck, 8 using the Joule-Thomson effect in air. 7 This method requires a, the 

 volume coefficient, as well as the Joule-Thomson coefficient /x. Roebuck mea- 



1 Bur. Standards Journ. Res., 1, 635, 1928. J Trav. et Mem. Bur. intern.} 13, 12, 1907. 

 'Ibid., vols. 6, 13. 4 Z. Phys., 5, 264, 1921 ; 5, 285, 1921 ; 37, 157, 1926. 6 H.P., 9, 527. 

 * Proc. Amer. Acad. Arts and Sci., 60, 537, 1925. T H.P., 2, 496. 



Smithsonian Tables 



