128 ANNUAL OF SCIENTIFIC DISCOVERY. 



vatory, by the old method. I have printed fifteen hundred wires with- 

 out fatigue, in one night, by the new. Since each wire is worth four 

 of those of the old method, we have six thousand to one hundred, or 

 sixty to one, as the relative efficiencies of the night's observations. 



" When we reflect that the probable error of one transit over one 

 wire is only the sixteenth of a second, and that with five wires it 

 is only a thirty-sixth part, or three hundredth of a second, it is man- 

 ifest that one tally, or five wires, is ample for all ordinary work. In 

 fact, one wire is sufficient for most of the purposes of astronomy. I 

 have been led, on consideration of all the facts known from the ex- 

 perience of the Coast Survey, to make the following remark relative 

 to the precision of our work, after proper adjustment of the transit 

 instrument, or measurement of its deviations from a normal state : 

 The printed transit of a fundamental star over any one wire of \Vur- 

 demanri's diaphragm, and that of a star, planet, or comet, whose place 

 is sought, over another wire, both reduced to the centre, on the suppo- 

 sition of uniformity of interval, give the place of the object sought 

 with a precision not much below that on which rest the present elements 

 of all the bodies in the solar system" 



SUBMARINE TELEGRAPH BETWEEN ENGLAND AND FRANCE. 



A GENTLEMAN by the name of Brett has obtained from the French 

 government the authorization to establish an electric telegraph be- 

 tween Calais and Boulogne, which, crossing the Channel under the 

 water, will go to Dover on the coast of England. The arrangement 

 entered into guarantees certain advantages to the French government, 

 and leaves all the expense to Mr. Brett, securing him, however, a 

 privilege for ten years, in case the experiment should succeed. The 

 work must be terminated by the 1st of September, 1850, at the latest 



Experiments to test the practicability of effecting an electric com- 

 munication beneath the surface of the ocean, for considerable dis- 

 tances, have recently been made at the harbor of Folkestone, Eng- 

 land. Upwards of two miles of wire, coated with gutta-percha, were 

 submerged in the sea along the mouth of the harbour. One end of 

 the wire was connected with a telegraphic instrument on the deck of a 

 steamer, and the other end with a wire communicating with the Lon- 

 don telegraph. Messages were sent back and forth with no greater 

 difficulty than with the ordinary wires on land. The insulation effect- 

 ed by gutta-percha is, no doubt, most perfect. The experiments of 

 Faraday have shown that it is one of the most perfect electrical insu- 

 lations with which we are acquainted. How far it may be acted upon 

 by the chlorine, iodine, &c., contained in sea waters, is a question 

 which has not yet been solved. 



The wire used in this experiment was, when covered with gutta- 

 percha, about a quarter of an inch in diameter; but this is much 

 smaller than that which it is proposed to stretch across the Channel. 

 It is believed that the kind of wire proper to be used, is the twisted 

 iron wire, coated so thickly with gutta-percha as to be nearly three 

 quarters of an inch in diameter. In order to guard against interrup- 



