[ i8i ] 
eonfequently the angles AEB and CFD are equaT. 
That is, the angle fubtended by the diftance of the 
centers of the fegments from the diftance of the 
focus of parallel rays is equal to the angle fubtended 
by the diftance between the objects A and B from the 
end of the telefcope. 
XXVIII. A Letter to Sir Peter Thompfon, 
Knt. F. R' S. containing Experiments on the 
Copper Springs in Wicklow in Ireland, and 
Observations thereon , by John Bond, M. D , 
SIR, 
Read May xo, ~XT OU may remember I had the ho- 
J(_ nour 0 f fpending an evening with 
you in June laft, and happen’d to mention a fpring 
in the county of Wicklow in Ireland, which was 
fuppofed to have the furprifing quality of changing 
iron into copper. But your conftant love of truth, and 
ftrong averfion to vulgar errors, made you doubt the 
fatt, which, at that time, I could only affirm on the 
report, which prevailed among the curious in that 
country. You then propofed fever al judicious que- 
ries, and feemed defirous of being further informed 
concerning it, which railed my curiofity to take the 
f rft opportunity of inquiring more particularly into 
the foundation of that marvellous account. 
Having foon afterwards occalion to go to Dublin, 
I went to the fpring, which is from thence about 
thirty-eight miles, and made feveral experiments on 
the 
