l8yy.] Recent Advances in Telegraphy. 361 
station, while the other half will flow by the branch v' into 
the artificial line, and so to earth. These currents being of 
equal potential as they pass the points c and d, no cross 
current between them will flow through the diagonal and 
the receiving instrument. A balance on the receiving in- 
strument will be obtained, and the sending at the home 
station will not affedt the receiving instrument there. The 
sending at the distant station, however, will still have con- 
trol over the home instrument, for by the stoppage of the 
line-half of the home-sending current the balance will be 
disturbed, and the home-receiving instrument will signalise. 
We have already seen, by help of the water analogy, in 
the case of the differential method, how that when only one 
station is sending a current only the receiving instrument 
at the station it is sent to receives it ; and that when both 
stations simultaneously send currents, both instruments 
signalise. The water analogy can also be readily applied 
to elucidate the same results in this method by supposing 
the real line and the artificial line to represent two equal 
streams of water flowing down equal channels. The condi- 
tions are so arranged that there is the same volume and 
head of water (potential) at the points c and d, and the 
same rate of fall of the level of the channels. In such a 
case, were a cross channel to be made between c and d, and 
a mill-wheel placed in it, there would be no cross current 
in it to turn the mill. But if by some means, such as 
shutting a sluice-gate, the stream in the line were suddenly 
dammed back, then the level of c would rise — a cross cur- 
rent would set in towards d, turning the wheel on its way. 
The adt of sending at the distant station is comparable with 
the closing of the sluice. 
The next important advances in duplex telegraphy were 
made in 1868, by Mr. Joseph Barker Stearns, an American 
eledtrician, who has done much to place it on its present 
footing. Stearns’s principal improvements were — the use of 
a peculiar key, which permitted the line always to be “ to 
earth ” through a constant resistance, and the addition of a 
condenser or other indudtive apparatus to the artificial line, 
so as to imitate the sensible induction of the earth on long 
land-lines. Stearns applied these improvements to both 
the differential and Wheatstone balance methods. Fig. 5 
shows their application to the former. He found that on 
land-lines of over 400 miles in length the sudden static 
charge due to the earth’s induction caused a sudden “ kick ” 
or false signal on the receiving instrument ; and in order to 
counteract it and secure the perfedt balance required, he 
