Cclxxii GENERAL SUMMARY OF SCIENTIFIC AND 



The performance of this and similar systems is deserving 

 of far more attention from the public than it has yet re- 

 ceived. 



Experiments have lately been made in Berlin with the 

 view of determining the adaptability of the electrical light 

 for military signaling. The light employed which was one 

 of great intensity was so arranged with an inclosed mirror 

 that the rays were projected against the clouds, which, serv- 

 ing as a screen, repeated on a gigantic scale in the sky the 

 signals Inade in front of the mirror. 



It is likewise of interest to record in this connection that 

 M. Gramme has communicated to the French Academy the 

 fact that he has effected substantial improvements in the 

 construction of his dynamo-electric machine, by the employ- 

 ment of the thin-plated magnets suggested some time since 

 by M. Jamin. By their use he is enabled greatly to aug- 

 ment the intensity of the currents. The new machines have 

 only one central ring instead of two, two electro-magnets in 

 place of four, their weight and size are greatly diminished, 

 and their capacities notably increased as compared with the 

 earlier machines. 



We recorded last year the invention by Messrs. Edison 

 and Prescott of the ingenious quadruples telegraphic instru- 

 ment, by means of which two messages may be sent in the 

 same direction and two others in the opposite direction si- 

 multaneously upon the same wire. A number of these instru- 

 ments have been introduced during the past year, and with 

 marked success. In this volume we may record the first 

 public trial of a discovery in telegraphy which promises 

 even more wonderful results, and by which it is affirmed, on 

 good authority, that at least sixteen messages can be sent 

 simultaneously over a single wire. The new system is the 

 discovery of Mr. Elisha Gray, of Chicago, and is termed 

 " the Electric-Harmonic Telegraph." The invention, which 

 has been practically developed during the past year, is at 

 present being tested upon the lines of the Western Union 

 Telegraph Company. 



Mr. Gray's system of multiple transmission is founded 

 upon the principle that composite tones are as readily trans- 

 mitted by a wire as single notes. The depression of each 

 key sets a self-vibrating electrotome in operation, which is 



