406 Miscellanies. 



upper or receiver plate of the electrophorus, be placed upon it and 

 touched, it will evince a very vigorous action on the electroscope. 



"This effect may be increased by the use of the condenser, and 

 even a common Leyden jar may be charged in favorable weather to 

 a considerable degree of intensity. 



"By a single contact of the plate of this electrophorus so much 

 electricity is sometimes developed, that it will communicate to a pin's 

 head, electricity enough to turn the stoall needle of the silk thread 

 torsion balance through two or three revolutions. 



" The non-conducting property of caoutchouc may be profitably 

 employed in the construction of torsion balances, for measuring the 

 intensity of electrical action. For this purpose a string of the gum, 

 of any convenient thickness, may be cut from a sheet or bag, making 

 it as nearly as practicable of uniform thickness. This may after- 

 wards be reduced to the required size by treating it with ether, 

 stretching it and allowing it to remain distended until the ether is 

 fully evaporated. A small longitudinal hole may then be made at 

 one end, through which a needle of gum shellac, carrying a disk of 

 metal, or what is better, a very thin spherical bag of caoutchouc at 

 one extremity, may be accurately adjusted on its centre of gravity, 

 Insulators of this substance may be formed either in plates, strings, 

 or conical portions of bags to support any required apparatus. 



"Hence it appears that nearly a complete set of electrical appara- 

 tus may be formed of this substance, capable of being transported 

 with perfect ease and safety under circumstances in which the com- 

 mon apparatus would be inevitably demolished. In a large bag, or 

 extended sheet, it may be used for the cylinder or plate of the com- 

 mon machine. A portion of the same may be substituted for the 

 rubber. The electrophorus, the condenser, and the Leyden jar 

 may be formed of it. The torsion balance constructed with balls of 

 this substance instead of pith balls, is an instrument far preferable to 

 that of Coulomb. The jar may receive either the coiled form al- 

 ready described, or it may have the usual form by making the inner 

 coating of tinned iron, covering it with a thin sheet of gum, and then 

 adding an exterior coating of metal." 



4. Geological remarks relating to Mexico^ ^c. in a letter dated 

 Mexico, May oOth, 1830, from William Maclure, Esq. — The 

 regular order of original stratification has been so much deranged in 

 this country by the intimate and frequent alternation of volcanic 



