( 2259 ) 
particulars he had not obferved in any Book extant to be truly 
and diligently handled^ 
Then he from the foundation raifeth a Theory concerning 
both Plain and Spherical Diopmcl{s^ zff\xmmg for a ground rhac 
rule concerning the Meafure of RefradionSj which Mr* Des- 
Cartes firft difcovered. and which now molt of the beft writers 
do admitj and which he judgeth agreeable to truth (for that all 
dedudiions from it very well fuit to experience J which yec he 
knows not that any writers have applyed to this purpofe^ fo as 
to have raifed any competent fuperftrudlure thereon. Arid 
here orderly (firft in refpe6fc to Plain^ then to Spherical Snr- 
faces^) confidering points radiating from a diftaiice fo great 
that their rays may be fuppofed to fall parallel to one another 
upon the refra<9:ing furface, he propounds fome Theorems\^ 
from which the chief Symptoms of refraded rays do refult^ 
their Interjedlions and Limits are eafily difcernable^ the ap- 
pearing places or images of fuch points are defined^ both in 
regard to an eye fituated/w the Axis of the radiation,, and in re- 
gard to one placed elfervhere. Then he profecutes in like man- 
ner the fame things in re fpe (St to Points^ radiating from a di- 
ftance fenfibly finite or near* 
And that the t?/^ of thefe things may be more readyj and 
ferviceable to pradrife, he fubjoyneth diftindly and particu- 
larly the determinations of the places in the Axis of the Ima- 
ges of points however radiating through each kind of 
tentes* 
Having difpatched thefe mattersghe toucheth generally con- 
cerning'the making ^judgment about theAppcarances of Mag* 
nitudes (z% to their fcituation and figure^) which follow thofe 
forts of reflection and refradion: Afterward more fpecially 
and copiouflyjhe fhews what kind of Images plain objeds do 
yeild from fuch r€fledions,and how they may be delineated* 
Among thefe things there are interfperfed fome confiderati= 
ons about divers incident raatters,as about the nature of Ligbr^, 
and the caufes of different Colours about the Rainbow, or co- 
lours appearing in pellucid globes 5 about fome appearances in 
the vitreous Ff^y?^^ ; concQrn'mgtlielinearefraBaria, concern* 
iiig the refolution of problems by Appropriate lines 5 concern- 
ing the properties of the Conical fedions in the refledion of In^. 
cidraysj&c^. 
IhU^iom^- 
