44 ESSAYS anp OBSERVATIONS 
ed rays, Sir Ifaac Newton * and feveral of 
his followers have fuppofed, that their par- 
ticles are of different magnitudes or den- 
fities: But, if there be any analogy be- 
tween gravity and the refractive power, it 
will produce equal perpendicular veloci- 
ties in all particles, whatever their mag- 
nitude or denfity be; and fo all forts of 
rays would be ftill equally refrangible. 
37- Ir feems therefore a more proba- 
ble opinion, which others have advanced, 
that the differently-coloured rays are pro- 
jected with different velocities from the 
luminous body: The red, with the great- 
eft ; violet, with the leaft; and the inter- 
mediate colours, with intermediate degrees 
of velocity: For, upon this hypothefis, it 
is manifeft, that they will be differently 
refracted in the prifmatic order; accor- 
ding 
been communicated to’the Royal Society by the Author, 
in a letter to the Reverend Dr James Bradley D, D, 
F.ReS.; yet it could not be omitted here, on account 
of its conneéion with fome of the queries that follow ; 
befides that it contains feveral illuftrations not to be 
found in the Tranfa@ions. 
* Newt, Opt. query 29. 
