June 19, 1921 scientific notes and news 287 



of the skin through which the test current entered and left the body. The 

 skin not only has a high and uncertain resistance, but in it there are capacity, 

 polarization, and possibly other effects which not only make the measure- 

 ments difficult but largely destroy their significance. It seemed, therefore, 

 that it might be of interest to measure the resistance of some parts of the 

 body not including those portions of the skin through which the test current 

 enters and leaves. To thus limit the parts whose resistance is to be measured, 

 use is made of four connections to the body. Two of these serve to lead the 

 test current to and from the body and two serve to bring the potential dif- 

 ference developed in a particular part of the body, as a result of the test 

 current, to a place where it can be measured. 



Ordinarily we understand the resistance of a conductor to be the ratio of 

 the drop in potential in it to the current flowing. However, when a conductor 

 has four terminals to which electrical connections can be made, the resistance 

 is understood to be the ratio of the drop in potential between the potential 

 terminals to the current entering and leaving through the current terminals. 

 In either case the potential considered should be only that caused by the cur- 

 rent and not that which may arise in some other way. 



In some of the measurements the left hand and the left foot were used as 

 a pair of current terminals, and the right hand and right foot as a pair of 

 potential terminals. Electrical connections to the hands and feet were made 

 by placing them in vessels containing a solution of common salt in water. 

 These vessels are either lined with metal, or contain a piece of metal having 

 a fairly large surface. Insulated wires are attached to the pieces of metal 

 or to the metal lining and serve as leads for connecting the body into the cir- 

 cuits used in making the measurements. The resistance of the four-terminal 

 conductor formed in this way is substantially the resistance of the trunk 

 of the body with all the connecting resistances and practically all disturbing 

 influences eliminated. 



In most cases the resistance has been found to be between 20 and 30 ohms. 



The paper was discussed by Messrs. Silsbee, White, C. A. Briggs, and 

 others. 



H. H. Kimball, Recording Secretary. 



SCIENTIFIC NOTES AND NEWS 



The following officers were elected at the annual meeting of the Maryland- 

 Virginia-District of Columbia Section of the Mathematical Association of 

 America, held at the drafting hall of the Capitol on May 7 : President, Oscar 

 S. Adams of the Coast and Geodetic Survey; Secretary-Treasurer, G. R. 

 Clements of the U. S. Naval Academy, Annapolis; Member Executive 

 Committee, F. D. Murnaghan of Johns Hopkins University, Baltimore. 



The National Geographic Society is sending an expedition this summer to 

 explore and study the Pueblo Bonito and Pueblo del Arroyo ruins in the Chaco 

 Canyon of northwestern New Mexico. The expedition will be led by Mr. 

 Neil M. Judd of the U. S. National Museum. 



Recent accessions in the Division of Plants of the National Museum include 

 400 specimens from China and New Caledonia, received as an exchange 

 from Mr. G. Bonati of Lure, France; 250 specimens of Chinese plants, 

 collected by Simeon Ten, purchased from the Arnold Arboretum in Boston; 

 and 713 specimens from Quebec, received as an exchange from the College 

 de Longueuil. 



