6l8 PHILOSOPHICAL TRANSACTIONS. [aNNO l/QO. 



arms, were confirmed, and served to correct the tables, so as to render them 

 more perfect. Fig. 6 represents the 7 satellites of Saturn, as they were situated 

 October 18, at il'^ 22"" 45^ The small star s served to show the motion of 

 the planet in a striking manner ; as, in about 34^ hours after the above-mentioned 

 time, the whole Saturnian system was completely moved away, so as to leave the 

 star s as much following the 2d and 1st satellites, which then were in conjunc- 

 tion, as it now was before the 2d. 



By comparing together many observations of the 6th satellite. Dr. H. finds 

 that it completes a sidereal revolution about Saturn in 1*^ 8^ 53™ Q^. And if we 

 suppose, with M. De La Lande, that the 4th is at the mean distance of 3' from 

 the centre of Saturn, and performs 1 revolution in 15"^ 22^ 34™ 38% we find the 

 distance of the 6th, by Kepler's law, to be 35^''.058. Its light is considerably 

 strong, but not equal to that of the 1 st satellite ; for, on the 20th of October, 

 at 19^ 56™ 46% when these 2 satellites were placed as in fig. 7, the 1st, not- 

 withstanding it was nearer the planet than the 6th, was still visibly brighter than 

 the latter. 



The most distant observations of the 7 th satellite, being compared together, 

 show that it makes one sidereal revolution in 22^ 40™ 46' : and, by the same 

 data which served to ascertain the dimension of the orbit of the 6th, we have 

 the distance of the 7th, from the centre of Saturn, no more than 27'''.366. It 

 is incomparably smaller than the 6th ; and, even in my 40 feet reflector, appears 

 no larger than a very small lucid point. The revolution of this satellite is not 

 nearly so well ascertained as that of the former. The difficulty of having a 

 number of observations is uncommonly great ; for, on account of the smallness 

 of its orbit, the satellite lies generally before and behind the planet and its ring, 

 or at least so near them that, except in very fine weather, it cannot easily be 

 seen well enough to take its place with accuracy. On the other hand, the 

 greatest elongations allow so much latitude for mistaking its true situation, that 

 it will require a considerable time to divide the errors that must arise from im- 

 perfect estimations. The orbits of these 2 satellites, as appears from many ob- 

 servations of them, are exactly in the plane of the ring, or at least deviate so 

 little from it, that the difference cannot be perceived. It is true, there is a pos- 

 sibility that the line of their nodes may be in, or near, the present greatest 

 elongation, in which case the orbits may have some small inclination ; but as he 

 has repeatedly seen them run along the very minute arms of the ring, even then 

 the deviation cannot amount to more than perhaps 1 or 2 degrees ; if, on the 

 contrary, the nodes should be situated near the conjunction, this quantity would 

 be so considerable that it could not have escaped his observation. 



From the ring and satellites of Saturn we now turn our thoughts to the 



