On the Agitations of the Lahe of Derwint Water. 163 



a«d lefs conftant, there are certainly many emanations wliicU 

 man cannot catch, or which would require a particular lludy 

 which it is feldom his intereft to apply to. 



It is poffible, alio, that fonie perfons, highly favoured by 

 nature, uiioht acquire, by long habit, au exact knowledge of 

 the quantitV of copper that exifts in any alloy ; but it is cer- 

 tain that thefe perfons could not communicate to others at a 

 diftance, or perliaps even prcfent, the kind of ienfations which 

 ihey experience, and their different modifications, according 

 to the nature and proportion of the mixtures. 



The means of diftinguifhing alloys, and the proportion of 

 alloys, by the help of fmell, appear then to me to form a fe- 

 condary charafter, which ought not to be neglciiled, and 

 which, in certain individuals, may, by habit, be brought to 

 perfe6lion, but which, as it cannot be eafily communicated, 

 can never become an eirenlial and comparalive characier. 



It is polFible that, in the time of Alexander, among the 

 means eafily put in practice, that of fmell was the fureii for 

 diflinguifliing the Indian vafcs of bronze fronxthofe of gold. 



In regard to the paifaoe of Herodotus, where it is laid 

 *' that pure gold was diftinguilhed by rubbing it againft other 

 gold," it appears to me that the word ■Trapcirp.-^'Ui.i.i'j mull be 

 retained, but the word ag.iinjl ought to be changed into hj 

 the JuL of. The paflage'"then becomes clear, and only fup- 

 pofes the emplovment of a hard body proper for retaining 

 the traces of thefe metals. 'I'his explanation alludes to that 

 kind of proof Itill pra6lifed by our goldfmiths, with plates 

 of metals alio\cd in known proportions, which are called 

 teft plates; but to be certain of their aflay, they make ufe of 

 a touch- ftone ; that is to fay, a common black ftone, not fiif- 

 ceptible of bein<i attacked by the acids which they pour upon 

 it, to afci^rlaiu the degree of. alteration in the traces left by 

 the alloys. 



XXVIIT. Sf.me O/'JcJ-i'i/lions on the Jgitations of the Lake of 

 Derwent llatefy and its f outing Ijlands. B}'. a Corre- 

 fpondent. 



To the Editor of the Philofophical Mergazine. 



PKcfwick, Oftobcr 7, iroi. 

 ASS IN G throu'ih this place with little time to fpare 

 from purfiiils not philofophical, I can onlv obtain iinperfci'-t 

 information ;d)out lonie curious phrenonuiia hitherto but little 

 jiolictdj by fome us little regarded as tales of tuchaniment, 



L Ji And 



