Wm. Herschel.
Slough, near Windsor,
March 3, 1789.
The third comet was discovered on the 7th January, 1790; the fourth on the 17th April of the same year, during her brother’s absence from home. It was announced to Sir Joseph Banks in the following letter:—
April 19th, 1790.
Sir,—
I am very unwilling to trouble you with incomplete observations, and for that reason did not acquaint you yesterday with the discovery of a comet. I wrote an account of it to Dr. Maskelyne and Mr. Aubert, in hopes that either of those gentlemen, or my brother, whom I expect every day to return, would have furnished me with the means of pointing it out in a proper manner.
But as perhaps several days might pass before I could have any answer to my letters, or my brother return, I would not wish to be thought neglectful, and therefore if you think, sir, the following description is sufficient, and that more of my brother’s astronomical friends should be made acquainted with it, I should be very happy if you would be so kind as to do it for the sake of astronomy.
The comet is a little more than 3½° following α Andromedæ, and about 1½° above the parallel of that star. I saw it first on April 17th, 16h 24ʹ sidereal time, and the first view I could have of it last night was 16h 5ʹ. As far as I am able to judge, it has decreased in P. D. nearly 1°, and increased in A. R. something above 1ʹ.
These are only estimations from the field of view, and I only mention it to show that its motion is not so very rapid.