f 4©39 ) 
j(J{ehti9n of tie Return of a Great permanent Spotin the Plane$ 
Jupiter^obfervedby Sigmr Caffini,<?»e of the J{oyai Pdriftan A* 
cademyofthe Sciences. 
'^-T-^I S now above fix year$,that $\gx\ovC(^ffint pub!iflied the 
J_ Theory of two forts o{ Spots.^t certain times to be ken 
in the Difque of Jupiter *. 
one fort are nothing but the Shadows of :fT^rJ^:Z7,i 
die four Satellits, which he had often very m thh fiamt henm. 
well obferved, when thefe SateUits, moving England h m. Hook 
through the lower part oi their imall circles ^,e/•^c«N».I.^3. cm- 
that environ fupiter^Aid: pafs between him ^^i'^'^'^^^^^^^f^^ 
and the Sua which illuminates him, making 2oVN^I5.^H6! 
a kind of Solar Eelipfe, like that which the 
Moon makethj when fhe is between the Sun and the Earthy 
1 hefe Spots,as be obferved^from that time, have this peculiar^ 
which diftingnifheth them from all others, that they are pre- 
cilely found in that place of J^fi^^r, where feme Satellit is feeo. 
by the Sun , that they go from the Orieotal limb to the Occk 
dental of the Difique oi Jupiter with a motion alwaiei equal to 
that of the Satellite that in refpefl: to us they preceed the Sa^- 
tellit before the oppofition of Jupiter to the Sun, and follow 
him after the oppofition i that the further Jupiter is diftanc 
from the oppofition^the greater is the apparent diftance of the 
fame Satellit, that s^t divers times of the Year this diftanc©: 
changeth in proportion of the annual Parallax of the. Satellite 
according as be is differently feen by the Sun and by the Earthy 
and that at one and the fame time of the year, when divers Sa-- 
teliits happen to be between Jupiter and the Sua , the Spots 
eorrefponcfent to them are diftant from them in proportion of 
the femi diameters of the circles of the fame SatelJits* 
The other fort of Spots have'no dependance at all from the 
SatellitSibut it feems,that they have fome refemblance to thole 
Spots that fometimes appear in the Sun^or to tbofe that are alf- 
waies feen in the Moon 5 and they are perhaps of the fame na- 
ture with thofe,that are called ^^/^/. Thefe Spots do alfo move 
from the Eaftern to the Weflern limb of Jupiter i difque 5 but 
their apparent motion is unequal, and fwifter near the Center 
than the Circumference , and they never are fo well feen as 
when they approach to the Center, they being very narrow: 
and almoft imperceptible, when they approach to the Circum- 
Pppp ferencet 
