166 TEAK-BOOK OP FACTS. 



all such defects are alleged to be certain to be discovered. A coil of 

 gutta-percha, from one mile to five, is placed in a strong cylinder 

 that can be made air and water-tight. The first operation is to 

 exhaust the cylinder ; when a vacuum is formed, a column of water 

 is allowed to rush in and fill up all the holes and crevices formerly 

 filled with air. The cable is in this state tested with a delicate gal- 

 vanometer and noted. A pressure is then applied equal to the pres- 

 sure of a column of water the height of which is equal to the depth 

 of the sea where the cable is intended to be laid, whether it be the 

 Atlantic or any other. This is continued for a certain time, when 

 the wire is again tested. On the pressure being removed, another 

 testing takes place, and it is affirmed that if the smallest defect in 

 the insulating medium, or mechanical injury, however minute and 

 invisible to -the naked eye, then exists, its detection is inevitable. 

 The disease can accordingly be removed or repaired, and the manu- 

 facture proceeded with. Finally, it appears that the whole expense 

 of the testing falls short of 5s. per cent, of the cost for making the 

 cable. — Times. 



ELECTRO-TELEGRAPHY. 



At the conversazione of the Royal College of Physicians, Professor 

 Wheatstone exhibited his New Printing Telegraph, .so constructed 

 that the message is sent by means of a perforated strip of paper, the 

 holes in which, representing the letters, are made by means of a 

 separate machine, worked by a finger-board. The advantage of this 

 method is, that several persons can work at the finger-boards, and 

 prepare several messages at once, and on the perforated paper being 

 put into the telegraphing machine, it forwards the message at the 

 rate of five hundred letters per minute, being about five times faster 

 than by the present system. On its arrival at its destination the 

 message is again pricked off on a paper tape, at the same rate, when 

 it can be easily and rapidly read. Another advantage is, that the 

 whole apparatus only occupies a few inches square, there being no 

 battery required, as it is worked by magnetic electricity. 



Professor Wheatstone also exhibited his Universal and Military 

 Telegraph, especially adapted for rifle and field practice. This is a 

 portable telegraphic apparatus, also worked by magnetic power. It 

 is extremely light, being only six inches square, ami is at all times 

 in readiness for immediate use, without previous preparation. The 

 communication in the field, or between the target and the gun, is 

 maintained in t ho ordinary alphabetical language by the most simple 

 means, so that any person who can read and spell is able to work it. 

 The communicating wire is covered witli rope, and is effectually 

 protected from abrasion or pressure when lying on the ground, though 

 of Comparatively small thickness, and when not in use can be rolled 

 on a drum. These telegraphs were used by the French in the late 

 Italian war, and are now in use in various public offices. The one 

 exhibited, although so small, forwarded messages to a distance of 

 twenty miles, but by increasing the size of the magnet much greater 

 power could be obtained. 



