442 On Electricity. 



difficult we may find it to form them at pleasure, and the rarity 

 of the occurrence only serves to prove that there are properties 

 and relations of this substance with which we are as yet unac- 

 quainted. An agreeable confirmation of this fact appeared some" 

 time after in an observation of Vaucpielin, copied in Tilloch's 

 Journal for 1S09, with which the members of this Society are 

 doul)tless well acquainted. In a geological view it may perhaps 

 be wortiiy of record, as not only establishing the volatility of 

 silica, but serving to prove that this substance may be crystal- 

 lized from the state of vapour, as sulphur, some neutral salts, 

 and somej metals are known to be. How far this property of 

 vaporization and erystallization from that state may be possessed 

 by the other earths, or by earthy compounds, as it undoubtedly 

 is l)y all the metals, must be determined by future observations. 

 Possibly we may thus gain a step on which to rest, in the investi- 

 gation of the diriiciilt .sul)ject of mineral veins, and the arrange- 

 ment of the crystallized substances which occupy their cavities. 

 The possibility also f)f explaining by tliis process the crystalli- 

 zation of the delicate filamentous zeolites wliich occupy the ca- 

 vities of amygdaloids, will readily occur to every mineralogist. 



LXX. On Eleciridfy. By Francis Ronalds, Esq. Com- 

 municnled by the Aiithoi . 



To Mr. Tilloch. 



Sir, — Jl5y a paper of Mr. De Luc, in your Number for October 

 last, I perceive that he has rather misconceived the inferences 

 which I drew from some experiments on the variable action of 

 the electric colunni, described in your Number 194; having 

 stated my opinion to be, that moisture has very little effect ou 

 that action. He seems also to imagine that the results of those 

 experiments were intended to be opjiosed to his, and refers to 

 some which were made with Dr. Lind, to prove that dryness di- 

 minishes the action. 



I cannot discover, however, that I have drawn such a con- 

 clusion, and had no intention to dispute with a philosopher of 

 iso great and universally acknowledged acuteness, the truth of 

 a fact which his own elegant experiments have fully esta- 

 blished. Had not the last paragraph of the paper above men- 

 tioned escaped Mr. De Luc's attention, I think the mistake 

 could not Iiave haj)pened. I there state as a probable cause of 

 the power of the column supported with three stems of glass, 

 not having been increased by a rise of temperature in its usual 



degree. 



