OPTICS. 
et Umbre. 
Maurolycus, B. Porta, Fletcher of 
Dominis, and to the articles TeLFscorgs and M 
: ; h 
fra€tion, and the nature of vifion. 
duced Kepler was ftill more diftinguifhed by Galileo, who 
threw new light upon almoft every fubje& of philofophical 
ufe of telefcopes, which we fhall more particularly notice 
under that article, he firft conceived the thoug 
furing the velocity of light, and he gives a particular defcrip- 
tion of his contrivance for this purpofe in his treatife on me- 
o 
2 
‘ 
gh Des Cartes was very eminent in the f{cience of 
optics, he does not ftand fingle in the period at which he 
lived. Befides Snellius, ‘who led the way tothe difcovery of 
ao 
3 
in the fame year with Des Cartes. He carried into execu- 
tion the {chemes of Kepler, for conftruéting telefcopes upon 
plans different from that of the original or Galilean one ; 
and fhares with Galileo the merit of difcovering the {pots of 
the fun. His treatife entitled «« Oculus’ is very valuable, 
and abounds with ingenious and important illuftrations of the 
nature of vifien. Gaffendi, alfo a contemporar es 
no particular difcovery in optics : 
ther among the fchoolmen than the philofophers. Du Hamel, 
Royal Academy of Sciences at 
optics 
e of the 
€ age 
He was about the fame age 
es Cart i i years. is 
** Ars magna Lucis et Umbra,” muft, at the time in whic 
it is written, have been confidered as a very capital per- 
angle of incidence. 
erfon who attempted to explain the caufe of refraction, 
which he did by the refolution of forces, on the principles of 
mechanics: fuppofing that light paffes with more eafe 
through a denfe medium than a rareone. The truth of this 
explanation was queftioned by M. Fermat ; who, in oppofi- 
tion to Des Cartes, afferted that light fuffers more refiftance 
e of reafoning, fee echales ex- 
plained the law of refraGtion by another hypothefis, which 
was adopted by Dr. Barrow, if he was not the author o it: 
or an account of this alfo we refer to REFRACTION. 
painted upon the naked retina. 
; and exhibited this curious experiment at Rome 
Scheiner particularly notices the cor- 
the camera obfcura, and 
nd refractive power of a : 
concludes, that the aqueous humour does not differ much 
5 from 
