Rotation of the fifth Satellite of Saturn. 15 
ture, in 1707, page 96; where we find the following para- 
graph. “ M. Cassini gives an example of the danger there is 
“ in these sort of determinations, that are made too hastily. 
“ The 5th satellite of Saturn, of which we have said, in the 
“ History of 1705, page 121, that it grew invisible, in the 
“ eastern half of the circle it describes about Saturn, began, 
“ in the month of Sept. 1705, to be there visible, as well as in 
“ the western half, where it always was so. Hence the con- 
“ jectures which we have related cease to be well founded.” 
Now, without determining whether the satellite, from some 
cause or other, ceased to change its brightness, or whether its 
phaenomena were not sufficiently followed to come to a proper 
conclusion, I think that with the assistance of observations at 
so great a distance of time as those of M. Cassini, I may suffi- 
ciently establish the period of this satellite's rotation. For 
since I have traced the regular, and periodical change of light, 
through more than ten revolutions, and find them, in all ap- 
pearance, to be contemporary with its return about Saturn, it 
leads us directly to a strong presumption that its rotation upon 
its axis, like that of our moon, strictly coincides with its re- 
volution round its primary planet; and the observations of 
M. Cassini completely confirm this conclusion. For, had he 
seen the satellite brightest in any other part of its orbit, our 
observations would not have agreed together ; but since the 
year 1705, the satellite has made about 397 revolutions; and 
yet the phaenomena described by Cassini answer now as ex- 
actly to my own observations, as the spots in our moon, viewed 
in Cassini’s time, answer to those we now observe. 
If it should be objected, that the 5th satellite of Saturn has 
not been continually observed, and that consequently these ap- 
