88 Mr. HERSCHEL on the 
poffible, and alfoto differ as much in magnitude as we can find 
them. 
Galileo, I believe, was the firft who fuggefted this me- 
thod ; but in the manner lie mentions it in his third dialogue 
of the Syjhma Cofmicum , it would be expofed to all the difficul- 
ties we have enumerated, and would wiffi to avoid ; for he does 
not obferve, that the two ftars fhould be lo near each other as 
thereby to preclude the influence of every caufe of error. 
This method has alfo been mentioned by other authors ; and 
we find that Dr. long obferved the double ftar which is the 
firff of Aries in ptolemy’s catalogue; that in the head of 
Caff or ; the middle one in the lword of Orion ; and that in the 
bread of Virgo, with telefcopes of fourteen and feventeen feet, 
and “ was perfuaded they would be found always to appear 
“ the fame.” But when the theory of parallax will be ex- 
plained, it will be feen that every one of thefe ftars are totally 
improper for the purpofe ; for the ftars of y Arietis are near io" 
diftant from each other, and moreover equal in magnitude. In 
Geminorum the ftars, though near enough, do not fuffi- 
ciently differ in magnitude to fhew any parallax. The ftars in 
the Nebula of Orion, on account of their extreme fmallnefs or 
diftance, are ftill more improper than any; and tliofe of y Vir- 
ginis are equal in magnitude. 
I do not find that any thing elfe has been done upon the fub- 
jedt. Galileo juftly remarks, that fuch obfervations ought to 
be made with the heft telefcopes, and upon this occafion mentions 
the power of his own, which enlarged the difk of the fun a 
thousand times, from which we find it magnified about thirty- 
two times ; but we can hardly think his nor even Dr. long’s, 
whofe power might probably be fixty or leventy, fufficient for 
the purpofe. What would galileo fay, if he were told that 
our 
