26 Mr. E. Gold : Relation between Periodic Variations of 



the thermodynamics of radiation. Accordingly a recalcu- 

 lation of molecular diameters becomes necessary. But it can 

 be carried out very simply because the best source of values 

 is data like that used for air by Jeans from its viscosity, 

 namely, No- 2 = 3306 cm. 2 , where a is the diameter of a molecule 

 of air. If we use for N the value of Rutherford in place of 

 4xl0 19 o-must be multiplied by the factor (4/2*77)*. On 

 applying this to the list previously given by me with allow- 

 ance for the effect of cohesional force we get the following 

 list of 10 8 times the molecular diameter in cm. 



H 2 . 



He. 



CO. 



2 H 4 . 



N a . 



Air. 



2-17 



1-92 



2-74 



331 



2-95 



2-86 



NO. 



2 . 



A. 



CO.,. 



N 2 0. 



Cl 2 . 



2-59 



271 



2-66 



2-90 



333 



3-76 



III. The Relation between Periodic Variations of Pressure, 

 Temperature, and Wind in the Atmosphere. By E. Gold, 

 M.A., Fellow of St. Johns College, Cambridge*. 



THE purpose of the following paper is to find expressions 

 for the variations in wind-velocity and in temperature 

 which must be associated with a given periodic variation of 

 pressure. The usual and perhaps natural method has been 

 to attempt to find the pressure variation and the wind which 

 must result from a given periodic temperature variation. 

 The problem viewed in this way is inherently so difficult 

 that it has been possible to solve it only on the assumption 

 that the atmosphere was a very thin shell in which vertical 

 variations could be neglected. The results were gratifying 

 inasmuch as they furnished a reasonable explanation of the 

 regularity of the semi-diurnal pressure-wave ; but there was 

 a great discrepancy between theoretical and observed phases. 

 For frictionless mofion, the phases of the diurnal pressure- 

 and temperature-waves ought, according to the theory, to be 

 the same; even for a large friction constant the difference of 

 phase is only 33° at the equator, and diminishes to zero at 

 the poles t« The observed phase-difference is with few ex- 

 ceptions as much as 100°-150°, the mean value for 18 stations 

 being 130°. For the semi-diurnal waves the phases ought 

 by the theory either to be the same or to differ by 180°. 

 Actually the mean observed difference for 18 stations is 83°. 



* Communicated by the Director of the Meteorological Office, 

 f Margules, Sitzungsberichte der Ah. der Wissenschaften in Wien,l$QQ, 

 1892, 1893. 



