PROCEEDINGS OF THE ACADEMY AND AFFILIATED 



SOCIETIES 



THE PHILOSOPHICAL SOCIETY OF WASHINGTON 



The 791st meeting was held at the Cosmos Club, May 26, 1917. 

 President Buckingham in the chair; 33 persons present. The minutes 

 of the 790th meeting were read in abstract and approved. 



Mr. C. F. Marvin gave an illustrated paper on Aerology in aid of 

 aeronautics. (No abstract.) 



Discussion: The paper was discussed by Messrs. Buckingham, 

 Hersey, White, and Sweet. Mr. Littlehales mentioned the sys- 

 tematic rotation of wind velocity with change in altitude. 



Informal communications: Mr. Humphreys gave an explanation of 

 the formation of the two kinds of sun dogs, or haloes, by reflection. 

 Mr. Buckingham considered one application of the principle of dimen- 

 sional homogeneity. In a communication about three years ago, the 

 speaker had enunciated a certain theorem concerning the forms of 

 physical equations, as a convenient formulation of the principle of 

 dimensional homogeneity. The present communication referred to 

 the further elucidation of the term "complete equation." By means 

 of Lord Rayleigh's problem of the gravitational oscillations of. a liquid 

 spheroid, two methods were illustrated for treating universal constants 

 which might be involved in the phenomenon described by the equa- 

 tion in question. It was further remarked that a similar choice of 

 methods was available for dimensional constants which were not 

 universal, and that one of the methods introduced a considerable 

 simplification into the algebra of the process. 



Donald H. Sweet, Secretary. 



543 



