1 70 Rev. J. B. Emmett on an Electrical Phcenomenom 



substance. The wall opposite to that now mentioned {g, 

 fig. 19), appears to be killas. The extreme steepness pre- 

 vented us from reaching this wall itself. A great many old 

 levels are to be seen in it, which appear to have been driven 

 for the puipose of raising tin ore. The granite is below the 

 killas in the cove (//, fig. 19). A layer, sometimes two inches 

 thick, is found at the junction of both rocks (near /, fig. 20), 

 consisting of very small but angular fragments of killas ; large 

 blocks of killas occur here imbedded in the granite. The 

 granite inclines very much to become decomposed, only at 

 (k k) it is fine-grained, harder, and partakes of the appearance 

 of porphyry (elvan); these places are not of great extent. 



The Beacon of St. Agnes consists of those varieties of 

 killas which are commonly found in the immediate neighbour- 

 hood of the granite. On the west side of the beacon occurs 

 a quartzose rock like that near Cligga Point; frequent pyra- 

 mids of quartz cover the surface ; clay is raised from a great 

 many shallow pits ; certainly the granite may not be far below 

 this place. We do not know whether the cliffs on the north 

 and west sides of the beacon exhibit any fact which may con- 

 firm or contradict this opinion. 



[To be continued.] 



XXIV. On an Electrical PJicenomenon. By t7ie Rev. 

 J. B. Emmett*. 



TTAVING constructed an electrical machine of uncommon 

 -■- -■- magnitude and power, an accidental circumstance led to 

 the discovery of a singular development of electricity. The 

 floor of the room in which the machine was placed being very 

 dry, I had occasion to have a wire of considerable length at- 

 tached to the cushion. My friend, Mr. Harwood of York, 

 first noticed a particular crackling sound to be emitted from 

 the wire, whenever a spark flew round the globe of the ma- 

 chine : on darkening the room, whenever a spark flew from 

 the prime conductor to the cushion, the whole of the wire was 

 found to be beautifully illuminated, throwing off, from points 

 about ^th or y^th of an inch asunder, a number of distinct 

 and separate pencils of electric light, to the distance of fths of 

 an inch. The wire first used was of copper, and about ^^th of 

 an inch thick ; but being desirous to ascertain to what distance 

 the effect might be extended, I substituted fine silver wire, not 

 more than ^^^th of an inch, and between 70 and 80 feet in 



* Communicated by the Author. 



length. 



