186 ESSAYS ann OBSERVATIONS 
in order to judge of thefe, I have computed 
the law of gravity towards fuch a fpheroid as 
‘ Fupiter; and will fubjoin fome theorems on 
this fubject. 
Ir feems fomewhat exraordinary, that 
in 130 years, fince Fupiter’s fatellites were 
difcovered by Galileo, no eclipfe of any of 
thefe fatellites by one another has been ob- 
ferved. Such an eclipfe could hold but for 
a {mall time: but, as it is not difficult to com- 
pute nearly the time when they ought to hap- 
pen, it would be worth while to look for 
them; fince this might contribute to render 
their theory more perfect; which is of fo much 
ufe in afcertaining the longitudes of places. 
If it be found to be a phenomenon that 
paffes over quickly, becaufe of their {wift 
motions; it may be the more ufeful, provi- 
ding it can be feen. 
No phenomenon feems more extraordi- 
nary, relating to Fupiter, than that, according 
to Caffinz, fome of his fpots revolve in lefs time 
than others; the difference amounting to 
4. This is a phenomenon, of that kind, 
of which it is perhaps beft not to attempt any 
explication, till the fame be confirmed by 
more obfervations. 
Ir 
- a a ee 
