Nov. 14, 1878] 



NATURE 



39 



direction more than one message at a time must be looked 

 upon as little more than feats in ' intellectual gjmnastics,' 

 very beautiful in their way, but quite useless in a practical 

 point of view." Such assertions should teach all scientific 

 writers the lesson of " hoping all things not impossible, 

 believing all things not improbable," an attitude of mind 

 which. Sir John Herschel remarks, should always charac- 

 terise the natural philosopher, and which, in the present 

 day, is certainly the safest one. Within six years of the 

 publication of the foregoing statement duplex telegraphy 



was not only largely employed in actual telegraphy, but 

 its use on certain busy lines became absolutely indis- 

 pensable. The change from theoretical to practical 

 success is due to an American, Mr. J. B. Steams, who 

 in 1872 succeeded in overcoming the main obstacle in 

 duplex telegraphy, namely, what is known as the static 

 discharge from the line. This Stearns accomplished by 

 using a " condenser " ; and further he developed a system 

 of " duplexing " the line similar to the principle of the 

 Wheatstone bridge. 



^ 





\ i V 



Fig. I. 



/ 



More or less successful attempts were afterwards made 

 to duplex submarine cables, and in the early part of 1877 

 Mr. J. Muirhead succeeded in duplexing the cables of 

 the Eastern Telegraph Company by his artificial conden- 

 sers. But we believe that his success was only partial. 

 Subsequently Mr. Muirhead has been at work duplexing 



/^' 



/^ 



'■^ 



SA 



\/' 



Fig. 



the Direct United States Cable with some prosp)ect of 

 success, and this week Steams, who may be called the 

 father of duplex telegraphy, has actually achieved the 

 great feat of perfectly duplexing the Anglo-American 

 Cable. In a message received by Mr. W. H. Preece 

 this week, Mr. Stearns says, " I managed to get some. 



Fig. 3. 



specimens for you this morning, though we had no time 

 to make the balance especially perfect for the purpose. 

 No. I shows signals received single ; No. 2, ditto, duplex. 

 No one can tell the difference. No. 3 is our balance 

 while keying, but not receiving. No. 4 shows the balance 

 perfect at first, but destroyed and restored again by the 



adjuster. It shows with what facility the ordinary adjust- 

 ments can be made after the balance is once obtained.. 

 The whole time occupied by slip No. 4 was about twenty 

 seconds." 



To understand these drawings our readers must know 

 that all the messages now sent across the Atlantic are 



V w' tf V "J y "v ' j 'i 



Fig. 4. 



automatically registered by means of Sir W. Thomson's 

 delicate and beautiful siphon recorder, which spirts out 

 little jets of ink in a fine stream on a moving ribbon of 

 paper. When no current passes the ink-marks form a 

 straight line, but a current causes this line to deviate to 

 the right or left, according to the direction of current. 

 Hence the ordinary right and left strokes of a needle 

 instrument or the long and short dashes of a Morse are 

 here indicated by marks above and below the middle 

 line. Thus the balance is shown by the almost perfectly 

 straight line in Fig. 3 and the messages in Figs, i and 2. 



The essence of duplex telegraphy is to obtain an 

 electrical balance round on the line such that the sending 

 instrument is not affected by currents circulating round 

 it coming from the sending end, but only by currents 

 received from the opposite end, and vice versd. Hence, 

 if the balance be once obtained, double transmission is 

 possible. This balance Steams has succeeded in obtain- 

 ing by the use of his system as applied to land lines, and" 

 without the aid of the additional arrangements of arti- 

 ficial condensers used by Dr. Muirhead. 



THE ROYAL SOCIETY MEDALLISTS 



'X'HE following are the awards of medals by the 

 J- Council of the Royal Society for the present 

 year. The medals will be given away at the Society's 

 anniversary meeting on the 30th inst. : — The Copley 

 Medal to M. Jean Baptiste Boussingault for his long- 

 continued and important researches and discoveries in 

 agricultvural chemistry; a Royal Medal to Mr. John Allan 

 Broun, F.R.S., for his investigations during thirty-five 

 years in magnetism and meteorology, and for his im- 

 provements in methods of observation ; a Royal Medal 

 to Dr. Albert Giinther, F.R.S., for his numerous and 

 valuable contributions to the zoology and anatomy of 

 fishes and reptiles; the Rumford Medal to M. Alfred 

 Comu, for his various optical researches, and especially 

 for his recent re-determination of the velocity of propa- 

 gation of light ; the Davy Medal to MM. Louis Paul 

 Cailletet and Raoul Pictet, for their researches, conducted 



independently but contemporaneously, on the condensa-: 

 tion of the so-called permanent gases. 



Jean Baptiste Boussingault was bom in Paris in 1802. 

 He was educated at the Mining School of St. Etienne, 

 after leaving which he became connected with an English 

 company formed to recover and work some mines ia 

 South America. This project, however, turning out un- 

 satisfactory, after a considerable time spent in scientific 

 travel in that continent, he returned to France and com- 

 menced those researches with which his name is more 

 closely allied, the most important of which lie in the- 

 domain of agricultural chemistry. Probably his investi- 

 gations of greatest value are those in which he has de- 

 termined the quantities of carbon, nitrogen, and hydro- 

 gen found in plants, and his comparison of these with 

 the amounts of the same constituents supplied to the 

 plant by manures, &c. During these investigations te 

 has shown, by a series of most conclusive experiments,, 

 the inaccuracy of the theory " that plants in their growth. 



