182 Miscellanies* 



When a wire of copper, gold, silver, or platinum, several yards 

 in length, bent in the form of an arc, and connected with the ends 

 of a galvanic multiplier, is gradually heated, an energetic current is 

 excited, the positive fluid passing from the heated point through the 

 end not heated, and the negative in the contrary direction. If the 

 heat is applied to a part of the wire which is not curved, no current 

 is produced. Iron, on the contrary, affords it in all circumstances. 

 Having arranged a circuit of ten, or even twenty yards of unheated 

 iron wire, the touch of the finger, or of any other object, or even 

 the motion produced by a change of position of any part of the ap- 

 paratus, was sufficient to induce an instantaneous current, dependant 

 apparently on the unequal pressure of the molecules in different por- 

 tions of the wire, and seeming to prove the truth of the supposition, 

 that a change of equilibrium merely is necessary to produce an elec- 

 tric current. — D. * 



32. On the use of locust wood for the timber work of subterra- 

 nean galleries; by M. Francois. (Ann. des Mines, T. vu, 3e liv. 

 de 1835.)-^-It has been a source of much expense, and not less in- 

 convenience, in the mines of France, that the timbers employed in 

 the subterranean galleries have been rapidly destroyed by the " dry 

 rot." The wood that is usually employed is the oak, and although 

 the timbers were of considerable size, (from three and a half to eight 

 inches in diameter,) they have seldom lasted longer than fifteen 

 months, and usually the greater part have been rendered unfit for 

 further use in the course of from three to seven months, and some 

 in fifteen or twenty days. The substitution of the locust was first 

 attempted by M. Chassignet, in 1830, whose fexperiments on this 

 subject proved satisfactorily its superiority to the oak. 



Under the influence of the subterranean heat, a yellowish viscous 

 substance is formed, which perfectly protects the alburnum from the 

 influence of the surrounding air. This viscous covering affords a 

 protection to the wood for about eight months. The alburnum is 

 then converted into a porous ligneous substance, to which the ulte- 

 rior preservation of the wood is probably owing, the inner parts re- 

 taining to an indefinite period the healthy soundness and firm texture 

 they possessed when first used. — D. 



33. On the cause of the " dry rot ;" by M. Aubuissox. (Idem.) 

 The first cause of this disease appears to be a fungous vegetation, 



