(i 7*) 
fore before thefe Obfervations. There remained to find by Ex- 
perience, whether Jupiter did turn about his Axis^ as many believe, 
that the Earth turns about her’s. And although mo&, Ajlronomers 
had conje<ftur’d 3 it did fo, either by this Analogy, or by other Con- 
gruities , yet it was much wiflfd,that we might be allured thereof 
by Obfervations* And this it is, for which we are obliged to 
M. Cajfini , who, having by the advantage of the fame Glaffes dif- 
cover'd feverai changes , as well in the three obfcure Belts , com- 
monly feen in Jupiter, as in the reft of his Disk?, and having alfo ob- 
ferved Spots in the midft of that Vianet , and fometimes Brightness, 
fuch as have bin formerly feen in the (San, hath at length difeover’d 
a Permanent Spot in the Northern part of the mo ft Southern Belt;, by 
the means \y here of, he hath concluded, that Jupiter turns about his 
Axis in 9. dayes r ,^ 6 . minutes, and makes 29. whole circumvolutions 
in 12. dayes 4. minutes of ours, and 360. in 149. dayes. For he has 
found.that this Spot was not caufed by the Shadow of any Sate Hit, 
as well by reafon of its Situation , as becaufe it- appeared , when 
there could be no Shadow. Beiides,that its motion differed from 
that of the Shadows, which is alraoft equal, as well towards the 
Edges as towards the Middle of Jupiter: Whereas, on the contra- 
ry, this Spot hath all the accidents, that muft happen to a thing, 
which is upon the furface of a round Body moving ; for example, 
to move much more flowly towards the Edges , than towards the 
Middle, and to pafs over that part, which is- in the middle of the 
Diske, equal to the half of the Diameter , in the fixth part of the 
time,it takes to make the whole revolutionise having feen this half 
pafs’d over, in 9 9 or rco minutes juft, as it muft happen, fuppofing 
the whole circumrotation is made in 9. hours 5 - 6 . minutes. 
He hath not yet been able to determine the Situation of the 
Axis-) upon wh'ch this motion is made, becaufe the Belts., according 
to which it is made, have for fome years appeared ftreight, though 
in the precedent years , other Aflrommers have feen them a little 
crooked ; Which fheweth, that the Axis of the diurnal motion of 
Jupiter is a little inclined to the plain of the Ecliptic ^ But in time 
we may difeover, what certainty there is in this matter. 
After this excellent Difcovery, he hath calculated many Tables, 
whereof he gives the Explication and Life in the Letters by him 
Th,f c TMc, an mt, ,t addrefled to the Abbot 1 Falccmeri. By the 
feat over, bnr, 3 tis hoped, means of them , one may know, when this 
will he, ere hng. ■ Spot may be feen by us: For, having firft con- 
fidered 
