C 26. ] 
XXXVIII. A Letter from Mr. T. Melvil to 
the Rev . James Bradley, D. D. F. R . S. 
With a Difcourfe concerning the Caufe of 
the different Refrangibility of the Rays of 
Light. 
S I R, 
Read March i,rT^HO’ I have not the honour of your 
I753 ‘ JL acquaintance, I have prefumed to 
addrefs the inclofed paper to you, relating to optics 
and aftronomy. The unwearied zeal which you have 
fhewn, Sir, for the improvement of thefe fciences, 
made me conclude, that whatever has an appearance 
of truth or novelty on fuch fubjects, tho’ inconfidera- 
ble in itfelf, might not be unacceptable to you. Be- 
fides, among all the focieties of the learned in Europe, 
I could think of no abler judge to confult on thefe 
matters, than the author of the “ Aberration of Light, 
“ and of the Variation of the Precefiion of the Equi- 
u noxes the two greateft difcoveries, without 
doubt, that have been made in aftronomy for half a 
century. Perhaps you may be able, Sir, from the 
many accurate obfervations you have already made, 
to decide the queftion relating to the velocity of light; 
or, at leaft, to determine, whether the obfervation 
propofed be practicable ; for I am very fenftble, that 
many obfervations, which appear eafy in fpeculation, 
cannot be put in execution. 
If you find any thing in the inclofed worthy of the 
public view, you are at liberty to lay it, in whole, or 
in. 
