of the magnetical Pyrites , &c. 317 
was struck with their resemblance to the pyrites of Breitenbrunn, 
which happened at that time to be in my possession ; and, upon 
trial, I found that they were magnetical, and agreed with the 
latter in every particular. Their magnetic power was such as 
strongly to affect a well-poized needle, of about three inches in 
length ; a piece of the pyrites, nearly two inches square, acted 
upon the needle at the distance of four inches. 
The powder (which is blackish -gray, with but little metallic 
lustre) is immediately taken up by a common magnet; but the 
pyrites does not act thus on the powder, nor on iron filings, 
unless it has been placed for some time between magnetical 
bars ; then indeed it acts powerfully, turns the needle completely 
round, attracts and takes up iron filings, and seems permanently 
to retain this addition to its original power. 
In the specimens which I obtained, the north pole was gene- 
rally the strongest. 
This pyrites was found in Wales, about the year 1798, by 
the Hon. Robert Greville, F. R. S. who sent the specimens 
above described to his brother, the Right Hon. C. Greville, 
with the following account. 
“ It is found in great abundance in Caernarvonshire, near 
“ the base of the mountain called Moel Elion, or probably with 
“ more accuracy Moel ^Elia, and opposite to the mountain 
“ called Mynydd Mawr. These mountains form the entrance 
“ into a little close valley, which leads to Cywellin lake, near 
“ Snowdon, a little beyond the hamlet of Bettws. 
“ The vein appears to be some yards in depth and breadth, 
“ and seems to run from north to south, as it is found on 
" Mynydd Mawr, which is across the narrow valley, and 
“ opposite to Moel /Elia” 
