59 
taken place in some antient alloys of copper. 
phenomena, which often seem to occur in the mineral 
kingdom ? These facts offer an obvious practical application, 
both in determining the antiquity and genuineness of ancient 
works of art ; for aerugo of the kind which I have described 
could not be successfully imitated by any artificial processes ; 
and a very slight chemical examination, or even one by the 
lens, would be sufficient to expose any fraud attempted to be 
practised by substituting modern imitations for ancient 
works. 
I am, most truly yours, 
J. DAVY, 
To Sir H. Davy , Bart. 
Pres. R. S. 
