68 E. V. Wcstmacott — On Bengal Gcocfraphy. [Feb. 



* In speaking of the Parganah of Barur, I should have said that it is in 

 both Parniah and Dinajpur districts. It is on the river Nagor. Can the 

 place Jor of which the Shikdar was also ruler be the Parganah Ajhor on 

 the frontier of Dinajpiir and Maldah ?' 



The President announced that the lectures for the ensuing month 

 would be — 



On the 11th " on the Polarisation of Light," b}" the Eev. Fr. Lafont. 

 On the 25th " on the Primitive Aryans," by Babu Eajendralala Mitra. 



The following papers were read — 



1. On the Theory of Duplex Telegraphy. By L. Schwendlee, Esq. 



This paper was read before the Physical Science Committee on the 

 8rd February, 1874, and was communicated to the Society the following 

 day. 



After having given a brief historical sketch of this important invention, 

 and after having stated the reasons of its non-introduction in practical 

 Telegraphy, Mr. Schwendler gave a short outline of his mathematical 

 investigation. 



The general results he obtained, may be stated as follows : 



" Considering the line as a variable conductor only, hut not acting 

 perceptibly as a Ley den jar, Mr. Schwendler found that hy using the Bridge 

 method, the hest resistance arrangement in either station ivould he that all 

 tlie hranches of the diagram, ivith the exception of the one ivhich lies opposite 

 to the line, should he made each eqiial to half the given line resistance; 

 while the hranch opposite to the line should have a resistance of one-sixth 

 that of the given line resistance. Further, that this hranch, the smallest of 

 all, should he invariahly used for re-estahlishing halance ivhen disturhed.'^ 



Under these circumstances, the following essential conditions, necessary 

 and sufficient to bring Duplex Telegraphy to success, are fulfilled. 



a. Any disturbance of halance has the least possible effect on the 

 regularity of the signals. {^Single and Duplex Signals.) 



h. If halance is disturbed it can he re-estahlished hy a single adjustment 

 {the greatest desideraticm in practice). This condition 3Ir. Schwendler calls 

 " immediate balance.'''' 



c. Maximum current. 



d. Maximum magnetic effect of Maximum current. 



Mr. Schwendler illustrated his investigation by an actual trial of the 

 method and proved by experiments, that having the best resistance arrange- 

 ments at either station, as indicated above, the variation in the line 

 resistance could be made far greater than would actually occur in practice 



