li 



Prof. W. B. Potter presented a communication, illustrated by 

 means of the estereopticon, on "Some Notable Examples of An- 

 cient Disintegration," in which he described and explained the 

 formation of the iron ore deposits at Iron Mountain and Pilot 

 Knob, Missouri. 



March i6th, 1891. 



President Nipher in the chair ; eight members present. 



Dr. Hinrichs described "Lippmann's Permanent Photographs 

 in Natural Colors," an account of which is published in the 

 Comptes Rendiis^ February 2, 1S91, and in La Nature^ Febru- 

 ary 14, 1 89 1. 



April 6th, 1 89 1. 



President Nipher in the chair ; nine members present. 



Dr. William Townsend Porter presented a communication on 

 " The Origin of the D'lcrotic Elevation in the Arterial Pulse," in 

 which he showed that the time interval between the j^rimary and 

 the dicrotic waves is the same in all arteries of the same indi- 

 vidual when curves simultaneously registered are compared. 



This result is in accordance with E. H. and Wilhelm Weber's 

 theory of wave transmission in elastic tubes, and is incompatible 

 with a peripheral origin of the dicrotic wave. 



April 20th, 1 89 1. 



President Nipher in the chair ; nine members present. 



Dr.Todd exhibited some specimens of ^(Sw^^a" Cicropia which 

 he had plucked from trees in the city, and called attention to the 

 fact that they were more numerous this spring in the city than he 

 had ever observed them before in either city or country. 



Mr. Seddon discussed the rate of travel of flood-waves down 

 our western rivers, concluding that the rate was the same at high 

 and low stages within the limits of overflow. 



