on the Rotation of the Planets , &c. tzt 
gravity, and the prefent rotation and given form of the earth, 
to find the centrifugal force required to produce that form, and 
thence to fhevv what mud have been its diurnal motion when 
it affumed the fame. However, thefe are refearches that in my 
prefent fituation I neither have opportunity nor perhaps ability 
enough to inveftigate properly ; and which, therefore, I hope 
feme 'of our excellent mathematicians will think worth while 
to look into. 
I fliall now relate my obfervations on Jupiter and Mars. The 
telefcopes I ufed are of my own con ft ruCtion ; and are, a 
twenty- feet Newtonian refledlor, a ten-feet refle&or of the 
fame form, and a feven-feet reflector already mentioned in my 
paper on the mountains of the moon. My time I gained by 
equal altitudes taken with a brafs quadrant of two-feet radius, 
carrying a telefcope which magnifies about 40 times ; for the 
correction of altitudes taken of the fun I ufed de la lande’s 
tables. I kept my time by two very good pieces ; one having 
a deal pendulum-rod, the other a compounded one of brafs 
and iron, both having a proper contrivance not to flop when 
winding up. The rate of going of my clocks I determined by 
the tranfit of ftars. 
Obfervations on Jupiter in the year 1778. 
February 24. Clock i' 10 " too foon. About 9 o’clock I 
faw a bright belt on one part of the dilk of Jupiter, fee tab, 
V. fig. 1. 
About 10 o’clock it was advanced as far as the center, fig. 2. 
II h. The white belt ftill more advanced, fig. 3. 
1 1 h. 25'. It approached towards the edge of the difk j and at 
12 h. was extended all over, as in fig. 4. 
Vol. LXXI. R February 
