1874.] President's Address. 49 



Up to the present the system adopted has been to examine under the 

 spectroscope the unknown alloy together with a check-piece of known com- 

 position, and it is found that the most minute differences can be detected. 



It will be easily seen then, that before a system of assay by this method 

 could be worked, an accurate map of the spectra due to all the gradations of 

 the alloy table would have to be made, which would be a work of much 

 labour and time, greatly increased by the fact that we constantly detect 

 the presence of several metals at one time in the bullion tendered to the 

 Mint. 



There is then much to be done, but still we look forward with great 

 interest to the perfection of the process, for in addition to any aid that 

 a trustworthy system of spectroscopic analysis will give to assaying opera- 

 tions, I have hope of deriving great assistance from it in our melting and 

 refining operations, In conducting the Bessemer steel process, the spectro- 

 scope has been of great service, of late it has been much used in Germany, 

 and it appears probable that it may prove to be in some degree useful in 

 the operations I have noted. 



In Electricity, only a few revivals and new applications have been made. 



Foremost is the revival of Duplex Telegraphy, ^. e. the method of send- 

 ing messages simultaneously along the same wire in opposite directions. To 

 Mr. Stearns, an American telegraph-angineer, it is due that this important 

 subject was prominently brought up again by his having actually succeeded in 

 introducing practically the long and well known methods of Duplex Tele- 

 graphy on some of the American telegraph lines. His success is due to the 

 introduction of condensers for the purpose of balancing the charge and dis- 

 charge of the line. Certain experiments were tried on the Indian lines in 

 November last year : the experiments which were made between Allahabad — 

 Calcutta and Allahabad — Jabalpur during October and November, were very 

 successful and showed the entire practicability of Duplex working. At 

 present arrangements are being made to finally introduce the system on one 

 of the important main lines between Calcutta and Bombay. 



The first and great requirement in connection with Duplex Telegraphy 

 is a general mathematical investigation to decide on the best method avail- 

 able, and for this method to calculate the best resistance arrangements and 

 distribution of condensers, required for any given line, overland or sub- 

 marine ; for the results of such an investigation would be a guide for practi- 

 cal telegraph-engineers to start Duplex working under the most favourable 

 circumstances and a paper on this subject, viz., on the general and particular 

 laws which regulate Duplex Telegraphy was yesterday read by Mr. Schwend- 

 ler to the Physical Science Committee. 



Referring to the Electro-Telegraphic determination of the differences of 

 Longitude on parallel 13° and in which I have already brought to your notice 



