Trench National Injlitute. 271 



thefe experiments at the houfe of C. Prony, and ftiowed that 

 plates of different metals are lengthened by a given and con- 

 ftant quaniity, from the temperature of ice to that of boiling 

 water *. 



The fec6nd caufe of elongation is eftiniated by a method 

 defcribed with great accuracy in Prony's memoir. 



The third was that of the greateft importance to be known 

 to the commiflion; for fonie archilci^ls entertained fears that 

 the edifice was finking. This movement, according to the 

 hypothefes of fome, by caufing the pillars, which are faid to 

 be too weak to fuilain the mafs, to give way, would have 

 crufhed them, and the dome would have funk vertically ou 

 itfelf. 



The poffibility of fuch a difaftrous effefl fuggefted to the 

 commiltion a dcfire to afcertain how far this was probable. 

 Prony has detailed, in his memoir, a great number of pre- 

 cautions which he took to ellimate this danger. After a 

 long and accurate inveftigation, he was convinced that no 

 alteration has taken place in the furfaces of the walls of the. 

 foundation, and particularly in the vertical direction of the 

 pillars ; that the parallelifm of the circular cornices of the 

 cupola is (lill preferved ; that the three domes are in no man- 

 ner affe<9;ed; and that an examination of the pillar which 

 has funk moft, proves it to be found. Thebliftering or foal- 

 ing off of the compofition which furrounds the pillars was 

 occafioncd therefore only by the finking of the latter, and 

 the finking arofc from an error in the conftruAion. But can 

 this finking make any progrtfs ? The attention of the com- 

 miffion will no doubt be dirccilcd to this object; and the in- 

 llrument invented by C. IVony is calculated to afcertain it. 

 New Galvanic Kxperimejits, 



ft appears that the idenlitv of galvanifm and electricity is 

 perfectly eliablUhed by recent fa<5ts. C. Biot Ins found that 

 the galvanic fluid in the different kinds of apparatus which 

 produce it, follows exactly the fame progrefs as electricity 

 would under the like circumfianccs. , 



Attraction and repulfion, indeed, being the fame in gal- 

 vanifm as in eleClricity, the aftion which the moleculse 

 exercife upon each other is the fame in the two fluids ; the 

 property which points poffcfs of tranfmittimr eledtrieity, and 

 which furfaces have to retain it, ought alfo to take place in 

 galvanilni; and, as the fmall plates may be confiderod as 

 more analogous to points tlian the large ones, they ought tti 



" TIrCc elongations are cliimattd at an SC^tli fprfteel, and a 000th for 

 *ift iron : the dilatation of foi^jcil and haminertrt irijn diiicr* very littie 

 trum ttiiu of Ik'c'l. 



give 



