I. Some Remarks on a late EJJay of Mr. Caffini, 
wherein he propojes to find, by ObferVation, the 
Parallax and Magnitude of Sirius, By Ed- 
mund Halley, LL. D. R. S. S, 
I N the Memoires of the Royal Academic of Paris , for 
the Year 1 7? 7. but now very lately publilhed, 
there is one very remarkable EfTay, by Mr. Caffini, con- 
cerning the Annual Parallax of the Fix’d Stars, and par- 
ticularly of Sirius 3 and in conclufion, he determines 
the Diameter of Sirius to be as much bigger than that 
of the Sun, as the Suns is greater than that of the 
Earth , which he fuppofes to be 100 times r And the di- 
ftance from the Sun to the Earth being certainly about 
1 00 Diameters of the Sun , it will follow, that the Globe 
of Sirius mud be a Sphere, whofe Diameter mud equal 
the diflance between the Earth and Sun. 
To prove this, he tells us that he made ufe of an 
excellent Telefcope of 34 French Feet, or 36 Englifh , 
leaving an Aperture of but an Inch and half, to take oft the 
fpurious Rays of the Star , which then appeared round, 
and fufficiently well defined; and comparing his Body 
to that of Jupiter , which he fays, was then 5 o Seconds 
Diameter, he found that the Diameter of Jupiter was 
ten times greater than that of the Star, which by con- 
fluence was feen under an Angle of about 5 Seconds ; 
which is his firfl Pofition. 
Then he tells us, that to make the Obfervations of 
the Parallax of this Star with all the exa&nefs poflible, 
he employed a Telefcope of three Foot , in a Copper 
A Tube, 
