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to the Top of the Obelifc a gilded Ball, whofe Ufe 
was to make the Shadow of the Extremity the more 
obfervable, as the middle Part of the Shadow of that 
Globe could readily be eftimated 5 whereas the Sha- 
dow of an Apex would, at fo great a Diftance, be 
intirely imperceptible. 
VX A Letter from the Rev . Mr. Mafon, 
Woodwardian Profejfor at Cambridge, and 
F. R. S. to the Pr. R. S. concerning Spelter, 
Melting Iron with Fit-coal , and a burning 
Well at Brofeley. 
SIR , 
Read Jan. 22 -Y T Aving met with feveral Things, in a 
1746 7 * IT! R am ble laft Summer, that were new 
to me, and imagining they might be fo to you like- 
wile, and being of fome Confequence, I prefume 
to trouble you with a fhort Account of fome of 
them. 
What Spelter is I don't well know, nor what Ufes 
are already made of it; but 1 believe it was never yet 
applied to fo large a Work as the Cylinder of a Fire- 
Engine, till Mr. Ford , of Colebrook-Dale in Shrop- 
pure , did it with Succcfs : It run eafier, and cart as 
true as Brafs, and bored full as well, or better, when 
it had been warmed a little: While cold, it is as 
brittle as Giafs, but the Warmth of my Hand foon 
made it fo pliant, that I could wrap a Shaving of 
it round my Finger likQ a Bit of Paper. This Me- 
tal 
