philosophical society of washington. 51 



28th Meeting. June 1, 1872. 



The President in the Chair. 

 Mr. Gr, K. Gilbert read a paper 



ON sand sculpture in the west. 



(abstract.) 



The author exhibited a number of specimens illustrative of the 

 work done by sand propelled by wind, and of the similar work 

 of sand propelled by water, accompanied by a few explanatory 

 remarks, in the course of which he called attention to the fact 

 that in river erosion the chief erosive agent is moving sand, and 

 the function of the water is the propulsion of the cutting par- 

 tides and the transportation of the eroded material, and to the 

 fact that in arid regions, where aqueous denudation is at a min- 

 imum, its place is taken by the denudation of wind-borne sand, 

 for which arid conditions are most favorable. 



Mr. J. H. C. Coffin and Mr. J J. Woodward read portions 

 ■of letters recently received from Dr. B. A. Gould, Director of the 

 National Observatory at Cordoba, Argentine Republic, giving 

 an account of the progress of that institution, 



Mr. J. J. Woodward made a verbal communication on the 

 Woodbury photo-relief process, exhibiting Woodbury-prints of 

 photographs reproduced by Mr. J. Carbutt at the establishment 

 of the American Photo-relief Printing Company for the Medical 

 History of the War. In his opinion the minute details of the 

 negatives were more faithfully preserved by this method than by 

 the Albertype process, and it was therefore preferable when natu- 

 ral objects of delicate texture were to be represented. It was 

 also well suited for reproducing photo-micrographs, as shown by 

 several proofs, which he also exhibited. 



Mr. E. Prisby read a paper 



ON a series for the determination of the number expressing 

 the ratio OF the circumference to the diameter. 



(^This paper is published in part in the Messenger of Mathematics, December, 



187:2.) 



