38 President's Address. [Feb. 



This part of the Journal has contained several other valuable papers, 

 among others that on Duplex Telegraphy by Mr. Schwendler. 



Turning to Physical Science, I would briefly notice the progress of those 

 branches that have been before this Society and such proceeding as may 

 be of interest. 



Duplex Telegraphy. — During the past year all the difficulties that 

 hitherto stood in the way of the practical application of Duplex Telegraphy 

 have been overcome, the system has been introduced and is working on the 

 Indian lines with perfect success. 



The double balance method was introduced on the 28th June, on one 

 of the main lines Calcutta — Bombay (1,600 miles,) since which date and 

 during the worst season of the year (south-west Monsoon) this method has 

 worked with great regularity and speed, and has carried nearly the whole of 

 the traffic between the two Presidency towns. 



In a few days another main line, Bombay — Madkas, will be worked by 

 this system, and it is probable that before the lapse of the current year, the 

 whole of the main traffic in India, Calcutta — Rangoon included will be 

 carried on this system. 



Experiments made at Bombay in July, with the Bombay — Aden cable 

 (1,800 knots in length) have conclusively proved that Duplex working with 

 the " double balance" method is also practicable on cables and it is to be 

 hoped that the Companies concerned will soon avail themselves of it, with a 

 view to increase the speed and reduce the charges. 



It has been mathematically demonstrated aud confirmed by practice 

 that the " double balance" method fulfils all the necessary conditions to bring 

 Duplex Telegraphy on a par with single Telegraphy. 



This method not only allows the balancing in the one station to be 

 effected without interfering with the balance of the distant station, but it 

 ensures, that unavoidable variations in the resistance of the line shall have 

 the least possible effect in disturbing that balance, and that all the other 

 conditions such as maximum receiving currents, and the maximum magnetic 

 effect of these currents shall be simultaneously fulfilled with it. 



In addition to these great advantages an automatic sj'stem of adjusting 

 the disturbed balance may be introduced, whence it follows that Duplex 

 working must be entirely on a par with single Telegraphy, and that where- 

 ever single Telegraphy is possible, Duplex Telegraphy is equally practicable. 



Thus one of the great standing problems in Telegraphy has been satis- 

 factorily solved on the large main lines of India, and the practical solution 

 of the second problem for long submarine cables, it is expected will soon 

 follow. 



The saving in outlay (capital) is very clear, for instance — at present 

 there is only one wire between Calcutta and Rangoon. The increase of 



