38 Mr. Tripe's Observations 



For determining weak electricities of charge, or as it is 

 sometimes called, of tension, I used Volta's condenser con- 

 nected with Bennet's electrometer, and sometimes with one 

 constructed on the principle of Behrens, consisting of an in- 

 sulated gold leaf, or what I found better, a silk filament, made 

 conducting by impalpable charcoal powder, to receive the 

 charge, placed between the poles of a dry pile consisting of 

 400 circles of silver and gold foil, of the third of an inch in 

 diameter, or 50 of zinc and silver of the same size, with paper 

 intervening; ihe attraction of the gold leaf or the filament, 

 either to the positive or negative pole, indicates the nature of 

 the charo-e : and, as in cases of electro-chemical action there 

 are always two corresponding opposite states, I considei'ed 

 the part of the system which touched the conductor as pos- 

 sessino- the same electrical state with that exhibited by the 

 leaf. I have never however put much dependence upon in- 

 dications given by this instrument, unless they were confirmed 

 by other results ; having found them very uncertain, and in- 

 fluenced by the state of the condenser and the atmosphere. 

 [To be continued.] 



XI. Observations on a Mineral from near Hay Tor, in Devon- 

 shire. By Cornelius Tripe, Esq.* 

 WHILE mineralogical science is so extensively cultivated, 

 and rapidly increasing in interest and importance, the 

 following brief description of a newly discovered mineral sub- 

 stance may not be unacceptable to the readers of the Philo- 

 sophical Magazine. 



The mineral alluded to was found in detached pieces, ac- 

 companied by small masses of chalcedony, garnet, actynolite, 

 talc, and very splendent octohedral oxidulated iron. These 

 substances, altogether, formed a single bunch of inconsiderable 

 size enveloped by a ferruginous clay, in a large lode of very 

 pure oxidulated iron, in an iron mine adjacent to the Hay Tor 

 granite quarries, Devonshire. 



Mr. Kennard, a respectable mineral dealer of Devonport, 

 personally assisted in removing the mineral from its situation, 

 and possesses the greater part which has been raised. I have 

 myself examined the mine since ; but with the most attentive 

 observation could not detect any further trace of the substance, 

 nor of the massive chalcedony, actynolite, or garnet, which, 

 as already stated, was found associated with it. 



The crystals, which are generally large and well defined, 



* Communicated by the Author. 



are 



