122 GERARDI REGNERl FOCKENS 



« mosjihere is so great, as lliat it will be hard lo discern o star jusl ali the horizon , or 

 (' eveii witliin some few degiees of it: and thal llic R.efraction would be liiere so grcat, 

 « and so uneertain , as not to comply with so curious an Observation." 

 Herschel (t): 



« Galileo, Ibelieve, was the firsl who suggested tliis mclhod ; but in tlie manner lie 

 « mentions it in bis third dialogue of the Sijstema C'osmicum, it would be expofcd lo 

 « all Ihe diHicullies we have enumerated , and would wisli to avoid ; for he doe? not 

 <i obscrve, that the' two slars should be so near each other as thereby to pveciude the in- 

 « fluence of every cause of error. " 



« This method has also been mentioned by other authors ; and we find that Dr. 

 « Long observed the double star which is tiie first of Aries in Ftolcmy's calaiogue ; 

 « that in the head of Custor; the middle one in the sword of Orion ; and that in the breast 

 « of Virgo, wilh telcscopes of fourteen and sevenleen fect , and « was pcrsuadcd they 

 « « would be found aivvays to appcar the same. " Bul when the theory of parallax 

 « will be explained, it will be seen that every one of these stars are lotally impro])cr 

 « for the purpose ; for the stars of y Arietis are near 10" distant from each other, and 

 « moreover equal in magnitude. In a Geminorum Ihe stars, though near enough , do 

 « not sulTiciently differ in magnitude lo sbew any parallax. The stars in the Ncbula of 

 « Orion , on account of their extreme smallness or distance , are still more improper 

 « than any; and those of y Virginis are equal in magnitude. " 



« l do not find that any thing eise bas been done upon the subject. Galileo juslly 

 « remarks , that such observalions ought to be made with the best telescopes, and 

 « lipon this occasion mentions the power of bis own , which enlarged the disc of the 

 « sun thousand times , from which we find it magnified about thirly two times; but 

 <( we can hardly think bis nor even Dr. Long's, whose power might probably be sixty 

 « or sevenly, sulTicient for the purpose. What would Galileo say, if he were told 

 « that our prcscnt opticians make instrumcnts that enlarge the disk of tbe sun above 

 « fourly thousand times? Wbat would even Cassini say, if he were to view the 

 ■« first star of Aries , which appeared to him as split in two , trough a telescope that 

 « will shew VI Coronae borealis and h Draconis to be double stars ? " 

 Von Zach ( • ) : 



« So finden wir denn auch wirklich, dass schon Galilaeus, einer, wir möchten wohl 

 u sagen , der Märtyrer der Lehre von der jährlichen Bewegung der Erde, sich in seinem 

 « Systema cosmicum sehr über den Mangel an tauglichen Beobachtungen zu diesem Behuf 

 •« beklagt und damals, wahrscheinlich um dadurch gewissermasseij ein Instrument von 



(. ei- 



(t)PAi7. Trans. 1782. LXXII, 88. 

 (*) Monatt. Corresp, 1809. XIX. 39. 



