Fig. 1.
... I will try to entertain you with some celestial affairs in which it is delightful to find you still taking so much interest. As you allude to Saturn’s satellites in your letter of October 20, I must tell you that I have at last got decisive observations of the sixth satellite (the farthest of my father’s new ones). I had all but given the search up in despair, when no longer ago than last Thursday (May 4th inst.), being occupied in taking measures of the angles of position of the five old satellites with the twenty-foot and a polished new mirror, behold, there stood Mr. Sixth! a little short of its preceding elongation. I have kept it well in sight from 14h 26m Sid. T. till 16h 35m, in which time it had advanced visibly in its orbit from below the line of the ansæ (as in figure) to above. In this interval the planet had moved over fully one diameter of the body towards the preceding side, and, therefore, had it been a star, must have passed over it, whereas it preserved the same apparent distance all the while from the edge of the ring. (N.B. Saturn not very far from the zenith on merid.)
Next night, Friday, May 5, Saturn most gloriously seen: quite as sharp as any copper-plate engraving, with power 240 and full aperture. All the five old satellites seen and measured, being now on the opposite side. Now considerably short of its greatest following elongation; distance just as before; and, as on Thursday, it was kept in view long enough for Saturn to have left it behind by its own motion had it been a star. The change of situation agrees perfectly with the period 1d 9h, which is also the reason why it was not seen May 5th, being on that night near its inferior conjunction. So this is at last a thing made out. As for No. Seven I have no hope of ever seeing it.
Fig. 2.
If your eyesight will not suffer from it, do write to Bessel. I am sure he will be interested by this observation, as he is the only astronomer who troubles himself about the system of Saturn. I shall myself write to him shortly about it, but should like to have a few more observations.
So now farewell once more, and, with many kind remembrances to all Hanoverian friends,
Believe me, your affectionate nephew,