196 



ted with the usual solutions of sulphate of copper and sulphuric acid. 

 A highly-polished steel plate was placed in a porcelain soup-plate, 

 and a "filtered solution of acetate of lead poured upon it. A piece 

 of card-board, out of which the required figures had been previously 

 cut with a sharp knife, was then placed upon a steel-plate. Over 

 the card, and resting on it, there was fixed a ring of wood, a quarter 

 of an inch thick, and the inner circumference of which was of the 

 same size as the figure. A convex copper-plate vras made so that 

 its outer edge might rest on the inner part of the wooden ring ; and 

 its centre placed near, but not in actual contact with the card-board. 

 Connexion was then made by the positive electrode of the battery 

 with the steel-plate ; the negative being placed in the centre of the 

 copper convex plate. The figure was generally obtained in from 

 15 to 35 seconds. If a concave, instead of a convex plate be used, 

 the same colours are obtained as in the former experiment, but in 

 an inverse order. 



" Geographical position of the principal points of the Triangula- 

 tions of the Californias and of the Mexican coasts of the Pacific, 

 with the heights of the principal points of that part of the Cordille- 

 ras." By the Comte Vincent Piccolomini ; in a letter addressed to 

 Sir John F. W. Herschel, Bart., V.P.R.S. Communicated by Sir 

 John Herschel. 



Hauteurs des principaux points des Cordilleres, des cotes de V Ocean 

 Pacifique du Mexique, et de la haute et basse Californie. 



Elevation en pieds 

 frangais sur le ni- 

 veau de la mer 

 pacifique. 



Volcano di Orizaba 18728 



Volcano di Popocatepetl.. 17812 



Volcano di Tztlacihuatl... 15698 



Riofrio 10948 



Real del Monte 10570 



Eloro 8995 



Tlalpuhahua 8435 



Ameia 8247 



Naupalucan 8194 



LasVigas 7918 



Perote 7911 



Ozmnba (Etat de Puebla) 7874 



Tepeyahualco 7702 



Ozumba (Etat de Mexico) 7620 



S. Rosa 7565 



Lagunas de Chalco 7510 



Mexico 7450 



Tepeaca 7444 



Huebuetaca 7121 



Puebla 7078 



Tula 6613 



Tlacotepec 6479 



Zacualpan 6181 



Elevation en pieds 

 frangais sur le ni- 

 veau de la mer 

 pacifique. 



Tasco 5971 



Temascaltepec 5760 



Guernavaia 5447 



Tcbuacan 5398 



Xantetelco 5030 



Cuicatlan 5028 



Oajaca 5024 



Cuautla 4587 



Talapa 4542 



Acayucan 4485 



Coscomatepec 4451 



Huatusco 4424 



Talostoc 4421 



Lautepec 4019 



Orizaba (%dUe) 3998 



Real de Christo 3851 



Huaitla 3336 



Cordova 2769 



Dominguillo 2274 



ViUale 1578 



Petapa 617 



Tehuantepec (Ocean Paci- 

 fique.) 132 



