170 GERARDI REGNERI FOCKENS 



« dius, so did il also Ihe length of tlie arch , or limb , on which the divisions were ma- 

 « de to adjust it. For Ihe arch could not conveniently be exlended faither, than to 

 « reach to about 6^'^ on each side my zenith. This indeed was sulHcient , since it gave 

 « me an opporlunity of makmg choice of several stars, very dilferent bolh in magnitude 

 « and Situation ; Ihere being more Ihan two hundred inserted in the British Catalogue 

 V that may be observed with it. I needed not to have exlended the limb so far , but 

 « that I was willing to take in CapeUa, , the only Star of the first magnitude , that co- 

 II nies so near my zenith." 



Protinus operae adnovit manum. Duodecim erant slellae , quas omni et anni et diei 

 tempore observavit. In his omnibus ejusdem generis sed diversae extensionis apparebat 

 niotus. Neque diu observavit, cum certam inveniret legem, cui hi motus obedirent t 

 ita tarnen ut aberraliones haud deessent. Ergo totum anni spatium voluil absolvi , an- 

 tequam hypolhesin assumerel ; ut quam exaclae observationes et quam stabilis sector 

 esset , certius judicare posset. 



Anno perlapso , legem phoenoraeni generalcm vidit confirmari. Ergo quaesivit cau- 

 sam. Nutatio non erat causa. Directio lineae plumbeae mutata haud magis satisfacie- 

 bat. Refraclio quoque abjiciebatur. Tandem conjecit , omnia haec phaenomena oriri e 

 progressiva lucis transmissione et annuo lelluris motu. Slalim indagavit , quaenam fo- 

 rent istius hypotheseos sequelae. Has salis ample indicat, Deinde observationes factas 

 cum phaenomcnis ex hypothesi computatis comparat. Ergo poslquam invenit rationem , 

 quae est inter velocitalem lucis et terrae, observationes ejusdem slellae diverso tempore 

 factas inier sese comparabiles reddit , adhibita praecessione regulari at tanta , quantam 

 darent ipsae observationes. Laiebat enira in slellis quaedam variatio ( nutatio ) , non- 

 dum explorata, sed hac via prudenter tractanda. 



Deinde e y Braconis radium circuli descripli invenit 20",2, id est rationem quaesilam 

 10210: 1 , unde sequilur , lucem a sole ad nos transmilti intra S" 12'. Sed Römeru» 

 ex eclipsibus salellilum Jovis invenerat 11", alii 7°. Ergo medium obtinet Bradleiua. 



« The different melhods of finding the velocily of light thus agreeing in the resuit , 

 « we may reasonably conclude , not only that these phaenomena are owing to the cau- 

 « ses to which they have been ascribed ; but also , that light is propagated ( in the same 

 « medium) wilh the same velocily after il halb been reflected as before : for this will 

 « be the consequence, if we allow that Ihe light of the sun is propagated with the 

 « same velocily , before it is reflected , as the light of the fixt stars. And I imagine this 

 « will scarce be questioned , if it can be made appear that the velocily of the light of 

 II all the fixt Stars is equal , and that their light movcs or is propagated Irough equa) 

 « Spaces in equal times , al all distances from them: both wich points ( as I apprehend ) 

 « are sufEciently proved from the apparent alteration of the declination of stars of diffe- 



« reut 



