236 TELEGRAPHY ACROSS SPACE. 



medium, such as water or moist earth, do not flow exclusively or even 

 mainly along the path of least resistance, but spread out, some flowing 

 along paths of greater resistance. If current enters a conducting 

 stratum at any point by a single electrode, A, and leaves it at some 

 other point by another suitable electrode, B, some of the current will 

 certainly flow straight from A to B ; yet the greater part will not so flow, 

 but will stream around from A to B in long curving paths. If then, 

 two other electrodes, and D, are inserted in one of these stream paths 

 at a distance from A to B, some of the current, perhaps only a small 

 percentage of it, may be picked up by a metallic line joining C to D. 

 Hence it is possible, using A B as a sending base line, to signal to C 

 D as a receiving base line at a distant place. The only limits to this 

 method of telegraphy across space are (1) the strength of the original 

 currents used in the sending base line A B; (2) the sensitiveness of the 

 apparatus used in the receiving base line CD; (3) the ratio between 

 the space distance from A B to C D and the lengths of the two base 

 lines. This system of telegraphing across space has been proposed at 

 various times. It has been used by Mr. Preece in several of those 

 many experiments which he has made from time to time, and which 

 will entitle liim to be regarded as one of the foremost pioneers in this 

 entire branch of telegraphic enterprise. 



Morse himself, as recorded in Vail's early work on telegraphy, 

 worked at this subject and made experiments in 1842 on the Susque- 

 hanna River, about a mile wide. He engaged Professor Gale to 

 investigate the best conditions, and came to the conclusion that the 

 base lines should be three times as long as the distance to be crossed. 

 Mr. Dering, an English telegraph engineer, and Mr. Lindsay, of 

 Dundee, have also worked in this direction. 



After the introduction, in 1877-78, of the Bell telephone, it was found 

 that the extraordinary sensitiveness of that instrument furnished a 

 new means of picking up currents that would otherwise be too feeble 

 to produce intelligible signals. The importance of this circumstance 

 in extending the possibilities of distance telegraphy was not lost upon 

 Mr. Preece. In 1882 he conducted a series of researches upon the 

 establishment of telegraphic communication between the Isle of Wight 

 and the Hampshire coast without any connecting cable across the 

 Solent. An account of these experiments will be found in the report 

 of the British Association for that year. Large metal plates, to serve 

 as electrodes, were immersed in the sea at the ends of the two base 

 lines. On the Hampshire coast the base line extended from Ports- 

 mouth through Southampton to Hurst Castle, a length of 20 miles. 

 On the island the base line extended from Ryde through Newport to 

 Sconce Point, and was about 16 miles long. From Portsmouth to 

 Byde the breadth of the sea is 6 miles, while Hurst Castle is only 

 about a mile from Sconce Point. Hence, in this case, the length of the 

 base lines considerably exceeded the average distance to be crossed. 



