4 02 TEE POPULAR SCIENCE MONTHLY. 



which the signals appear to have been given by the deflections of a 

 single needle. Sir Francis Ronalds, before 1823, sent intelligible mes- 

 sages through more than eight miles of wire insulated and suspended 

 in the air. His elementary signal was the divergence of the pith- 

 balls of a Canton's electrometer produced by the communication of a 

 statical charge to the wire. He used synchronous rotation of lettered 

 dials at each end of the line, and charged the wire at the sending end 

 whenever the letter to be indicated passed an opening provided in a 

 cover ; the electrometer at the far end then diverged, and thus in- 

 formed the receiver of the message which letter was designated by the 

 sender. The dials never stopped, and any slight want of synchronism 

 was corrected by moving the cover. 



Weber and Gauss carried out Schilling's plan in 1833 by leading 

 two wires from the Observatory of Gottingen to the Physical Cabinet, 

 a distance of about 9,000 feet. The signals consisted in small deflec- 

 tions of a bar-magnet, suspended horizontally with a mirror attached, 

 on the plan since adopted in Thomson's mirror galvanometer. 



At their request, the subject was earnestly taken up by Prof. Stein- 

 heil, of Munich, whose inventions contributed more perhaps than those 

 of any other single individual to render electric telegraphs commer- 

 cially practicable. He was the first to ascertain that earth-connections 

 might be made to supersede the use of a return wire. He also in- 

 vented a convenient telegraphic alphabet, in which, as in most of the 

 codes since employed, the different letters of the alphabet* are repre- 

 sented by different combinations of two elementary signals. Two 

 needles were employed, one or the other of which was deflected ac- 

 cording as a positive or a negative current was sent, the deflections 

 being always to the same side. Sometimes the needles were merely 

 observed by eye, sometimes they were made to strike two bells, and 

 sometimes to produce dots, by means of capillary tubes charged with 

 ink, on an advancing strip of paper, thus leaving the permanent rec- 

 ord on the strip in the shape of two rows of dots. His currents were 

 magneto-electric, like those of Weber and Gauss. 



The attraction of an electro-magnet on a movable armature fur- 

 nishes another means of signalling. This was the foundation of 

 Morse's telegraphic system, and was employed by Wheatstone for 

 ringing a bell to call attention before transmitting a message. 



About the year 1837 electric telegraphs were first established as 

 commercial speculations in three different countries. Steinheil's sys- 

 tem was carried out at Munich, Morse's in America, and Wheatstone 

 and Cooke's in England. The first telegraphs ever constructed for 

 commercial use were laid down by Wheatstone and Cooke on the 

 London & Birmingham and Great Western Railways. The wires, 

 which were buried in the earth, were five in number, each acting on a 

 separate needle ; but the expensiveness of this plan soon led to its 

 being given up. The single-needle and double-needle telegraphs of 



