I. 
PAPERS OF THE PHYSICAL GLASS. 
I. ExPERIMENTS 4nd OBSERVATIONS on the UNEQUAL RE- 
- PRANGIBILITY of Licut. By RoBERT BLair, M.D. 
' _ [Read Fan. 3. and April 4. 1791.) 
I) Y the difcovery of the different refrangibility of light, Sir 
Isaac NewrTon laid open the true caufe of the principal 
_ imperfetion of refracting telefcopes ; and having inferred from 
_the experiments which he made, that the refraction of the dif- 
ferent rays compofing the prifmatic fpectrum, was always in a 
given ratio to the refraction of the mean refrangible ray, this 
great philofopher was led to conclude, that the imperfection 
which he had difcovered in dioptrical inftruments was without 
remedy. 
Ir Sir Isaac Newton had been queftioned concerning the 
poflibility of refracting light, without any divergency of the 
heterogeneal rays, his reply without doubt would have been, 
that all his experiments, whether by fingle refractions or by 
oppofite refraétions, tended to eftablifh the contrary conclufion. 
But that he would have afferted nothing beyond this, may fafe- 
ly be inferred’ from his own memorable words: “ Although 
“ the arguing from experiments and obfervations by induction 
“ be no demonftration of general conclufions, yet it is the beft 
bs ee “* way 
