NATURAL PHILOSOPHY. 149 



of wire rope, or other means of protection. The present patentee has 

 discovered that a metallic circuit, formed of wires, either wholly uninsu- 

 lated, or partially so, may be employed for an electric telegraph, provided 

 that the two parts of the circuit are of such a distance apart that the 

 electric current, or a portion of it, would meet with more resistance in 

 passing from one wire to the other, by the water or the earth, or by 

 imperfect conductors which the wires may be attached to or suspended 

 from, than in following the wire. For this purpose he causes the two 

 wires, (which may be of plain galvanized iron, either uninsulated or 

 partially insulated by a coat of varnish or otherwise,) of which a circuit of 

 an electric telegraph is to be formed, to be placed in the water or earth, at 

 a distance apart proportionate to the total length of the circuit. These 

 wires he insulates where they approach one another, to communicate with 

 the instruments and battery or source of electricity, or with a continuation 

 of conductors for carrying on the current, in order to prevent the current 

 passing through the diminished space between the wires. And in the case 

 of intermediate stations, the wires are insulated in each direction from, the 

 instruments, in order to insure the current making the circuit of the 

 instruments, and not passing in a large proportion through the earth or 

 water, or other conductors, between the insulated parts of the wire on each 

 side of the station. By these means the cost of the laying down of electric 

 telegraphs, whether submarine or otherwise, is by means of this invention, 

 of employing distance between the conductors as a means of insulation, 

 reduced to little more than the mere cost of the conductors for the current, 

 together with that of an insulated wire at each end of the line to complete 

 the circuit between the extremities of the insulated conductors ; and the 

 numerous difficulties which attend the insulation of long lengths of wire 

 are avoided, as also the chances of the communication being interrupted 

 by accidents to the insulation. 



ON THE MAGNETIS3I OF ROCKS. 



At a recent meeting of the French Academy, M. Regnault communi- 

 cated the result of some new researches into the magnetism of rocks. He 

 has found out that, besides being feebly attracted by the magnet, they have 

 polar magnetism, which makes them capable of acting by attraction and 

 repulsion on the poles of a neighboring magnet. M. Melloni attributes 

 the tardiness of this discovery to the great weakness of the repulsive 

 action, which renders it necessary that the experiment should be made at 

 a very short distance from the magnetic needle, and this proximity 

 develops in the nearest parts of the mineral attractive forces of reaction, 

 whose intensity is greater than the repulsive action natural to the rock. 

 To exhibit the feeble magnetism of mineral substances, he urges experi- 

 menters to use an instrument he has invented, and which he calls the 

 maguetoscope. 



