Rotation of the Planet Saturn upon its Axis . 6‘i 
for this purpose I select Dec. 18. T 19', Jan. 2. i h 52' ; and 
bringing them also to true mean time, we have. 
From Dec. 4. 13 11 46' 51" to Dec. 18. 7 h 19 ' 28" an interval 
of 13 days i7 h 32' 37". Then, supposing 32 revolutions to 
have been made, we obtain a period of io h 17' 54". Also, 
From Dec. 4. 13 11 46' 51" to Jan. 2. 6 h 53' 11" is an interval 
of 28 days iy h 6' 20"; and admitting 67 revolutions of the 
belts, the period will be io h 17' 6". 
These trials of intermediate times agreeing with the former 
sufficiently well, there can remain no doubt about the true 
quantity of the period in general. I therefore take a mean of 
the two first determinations, which gives io h 16' 15", 5 for the 
approximate rotation of Saturn upon its axis. 
It now becomes necessary to construct tables for a general 
calculation of all the observations. For, if these should con- 
tain descriptions contradicting the calculated appearances of 
the quintuple belt, our assigned period could not be looked 
upon as sufficiently established ; on the contrary, if the calcu- 
lated and observed appearances are found to agree, we may 
rest satisfied that the rotatory motion of this planet, which has 
so long eluded our strictest attention, is at length obtained. 
In consequence of a few trials, which were made after the 
7th of January, by tables constructed upon this mean period, 
I found that some small correction was required ; and obtaining 
another very good observation on the 16th of the same month, 
it gave me an interval which included one hundred revolutions 
of the equator of Saturn. Now, making the proper deduction 
for the planet's retrograde motion during the time that passed 
between the first and last observation, we have from Dec. 4, 
1 3 h 46' 51" to Jan. 16. 8 h 25' 39" an interval of 42 days 
