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XCVIII. An Account of fotne Experiments 
concerning the different Refrangibility of 
Light. By Mr. John Dollond. With a 
Letter from James Short, M.A. F.R.S. 
Acad. Reg. Suec . Soc. 
To the Rev. Dr. Birch, Secret. R. S. 
Dear Sir, 
Read June 8 , y Have received the inclofed paper from 
I7 5 8 - Jp Mr. Dollond, which he defires may 
be laid before the Royal Society. It contains the 
theory of correcting the errors arifing from the dif- 
ferent refrangibility of the rays of light in the ob- 
jeCt-glaffes of refraCting telefcopes ; and I have found, 
upon examination, that telefcopes made according to 
this theory are intircly free from colours, and are as 
ditf inCt as reflecting telefcopes. I am, 
Dear Sir, 
Surrey-flreet, 
8th June, 1758. 
Your mod obedient humble Servant, 
Ja. Short. 
I 
T is well known, that a ray of light, refraCted 
by pafling thro’ mediums of different denfities, 
is at the fame time proportionally divided or fpread 
into a number of parts, commonly called homogeneal 
rays, each of a different colour ; and that thefe, after 
refraCtion, proceed diverging : a proof, tha^^eyare 
