On Slaffa. 445 • 



diameter and more pressed together, the effects were much less 

 striking, ahhough they were fully sufficient to prove that no more 

 electricity escaped by the insulators or the air from the upper 

 extremity when the latter was moistened than when it was drier. 



I would draw from these experiments the following con- 

 clusions ; but I do not wish to insist very confidently on their 

 validity. , 



1. The quantity of electricity arriving at a certain intensity, 

 which a column of this kind is capable of manifesting, as mea- 

 jmred by the vibrations of the pendulum apparatus, or the stiikings 

 of a gold-leaf electrometer, in a given time, is great in proportion 

 to its degree of moisture within certain limits. 



2. Under certain circumstances this greater quantity, thus 

 manifested in a moist state of the column, does not produce 

 greater intensity than when it is in a drier state. 



3. Since electricity does not pass off in one of the above 

 cases bv the insulators or the air more copiously than in the other, 

 it must pass by the water, which is tlie cause of its accumulation ; 

 otherwise the intensity would be proportional to the quantity. 



4. If the last proposition is correct, the great quantity and 

 low intensity of the electricity produced by Voltaic batteries 

 charged by acids and salts, may be attributed to a similar cause. 



I am, sir, your huml)le servant. 

 Hammersmith, Dec. IG, 1814. FranCIS RoXALDS. 



LXXI. Oji Slaffa. By J. MacCulloch, M.D. F.L.S. Che- 

 mist to the Ordnance, and Lecturer on Chemistry at the Royal 

 Military Academy at Woolwich. F. Pr. Geol. Soc* 



If the " Description and Natural Hist^4•y" of Staffa, by Faujas 

 de St. Fond, or the various other descriptions which have been 

 published of this island by naturalists and by tourists, had ex- 

 hausted the subject, I should have forborne to iiave troubled the 

 Society with any remarks on a place which ought now to be well 

 known. 



But a visit to this celebrated island having given me an op- 

 portunity of remarking a circumstance before unnoticed, and of 

 some importance in its natural history, I think it my duty to lay 

 it before the Society. In so doing, I find it difficult to avoid 

 etitering rather minutely into the general description of the island, 

 particularly since a second examination, besides confirming the 

 remarkable fact I at first noticed, has enabled me to investigate 

 its structure more completely. I shall doubtless still leave some- 

 tliing to be corrected by those who may come after me. A 



* From tlie Geological Transactions, vol, ii. 



multiplicity 



