226 Things not generally Known. 



the receiving station ; two persons at a distance may pro- 

 nounce several syllables at the same time, and each hear those 

 emitted by the other. So, on a telegraph-line of two or three 

 thousand miles in length in the air, and the same in the 

 ground, two operators may at the same instant commence a 

 series of several dots and lines, and each receive the other's 

 writings, though the waves have crossed each other on the way. 



EFFECT OF LIGHTNING UPON THE ELECTKIC TELEGRAPH. 



In the storm of Sunday April 2, 1848, the lightning had a 

 very considerable effect on the wires of the electric telegraph, 

 particularly on the line of railway eastward from Manchester 

 to Normanton. Not only were the needles greatly deflected, 

 and their power of answering to the handles considerably weak- 

 ened, but those at the Normanton station were found to have 

 had their poles reversed by some action of the electric fluid in 

 the atmosphere. The damage, however, was soon repaired, and 

 the needles again put in good working order. 



ELECTRO-TELEGRAPHIC MESSAGE TO THE STARS. 



The electric fluid travels at the mean rate of 20,000 miles 

 in a second under ordinary circumstances ; therefore, if it were 

 possible to establish a telegraphic communication with the star 

 61 Cygni, it would require ninety years to send a message there. 



Professor Henderson and Mr. Maclear have fully confirmed 

 the annual parallax of a Centauri to amount to a second of arc, 

 which gives about twenty billions of miles as its distance from 

 our system ; a ray of light would arrive from a Centauri to us in 

 little more than three years, and a telegraphic despatch would 

 arrive there in thirty years. 



THE ATLANTIC TELEGRAPH. 



The telegraphic communication between England and the 

 United States is so grand a conception, that it would be impos- 

 sible to detail its scientific and mechanical relations within the 

 limits of the present work. All that we shall attempt, there- 

 fore, will be to glance at a few of the leading operations. 



In the experiments made before the Atlantic Telegraph was 

 finally decided on, 2000 miles of subterranean and submarine 

 telegraphic wires, ramifying through England and Ireland and 

 under the waters of the Irish Sea, were specially connected for 

 the purpose ; and through this distance of 2000 miles 250 dis- 

 tinct signals were recorded and printed in one minute. 



First, as to the Cable. In the ordinary wires by the side of 

 a railway the electric current travels on with the speed of light- 

 ning uninterrupted by the speed of lightning ; but when a 

 wire is encased in gutta-percha, or any similar covering, for sub- 



