. The Electric Column considered a5 a maintaining Tower. 359 



be specimens of native chrysocoUa; they proved indeed to be 

 carbonate of copper, but it had formed round longitudinal nuclei 

 of red oxide of copper, so that probably these substances had 

 been copper nails or small pieces of copper used in the building, 

 convei ted by the action of the air, during so many centuries, into 

 oxide and carl)onate. 



The ancients, as it appears from Theophrastus, were well 

 acquainted with verdi,^rise. Vitmvius mentions it amongst 

 pigments; and probably many of the ancient greens, which are 

 now carbonate of copper, were originally laid on in the state of 

 acEtite. 



The ancients had beautiful derp green glasses, which I f.nd 

 are tinged with oxide of copper ; but it does not appear that 

 thev used these glasses in a state of |)o\vder as pigments. 



The greens of the Aldobrandiui picture are all of copper, as 

 was evident from the action of the muriatic acid upon thenu 

 [ I'o be continued. j 



LXIV. The Electric Column considered as a maivta/Jiing 

 Power, or First Mover for mechanical Purposes. By GuoiiGH 

 John Singer, Eiq. 



J. HE power of the electric column as a source of meclianlesl 

 action, was fust discovered and applied by tliat excelleut pliilo- ' 

 isopher M, De Luc, the admirable inventor of that important 

 instrument; and it is to his active discrimination and unceasing 

 exertions we are indebted for the principal mechanical arrange- 

 ments which have been emjjloyed to render the variable action 

 <if the column equal to the production of a constant though un- 

 equal motion. 



The principal object of such an attempt is to enable an ob- 

 server to measure the actual variation iu the power of the column 

 a' different times, and under dissimilar circumstances ; and, by 

 a comparison of these changes with the usual meteovological 

 piiaenomena, to ascertain if any connexion can be traced between 

 tiie spontaneous electricity r.f the column, and the natmal elec- 

 tricity of the earth and the atmosphere. 



For this purpose any arrangement may be employed which is 

 capable either of producing or maintaining the motion of light 

 substances by the immediate action of the column; and that will 

 be most eligible which produces this effect mostt certainly, and 

 fey the least complex means. 



With columns of small power, the frequency with which tlie 

 leaves of Beuuet's electrometer are made to open, and strike the 



/, 4 sides 



