Below we present brief extracts from William Herschel's first five papers published by the Royal Society up to, and including, the paper where he discovered the planet Uranus but, unsure whether it was a planet or a comet, he announced it as a comet.
1. Astronomical Observations relating to the Mountains of the Moon.
Read: 11 May 1780.
At the time when the telescope was first invented this noble instrument was immediately applied to astronomical observations with the most surprising success. Several very eminent persons have given us an account of their discoveries; and, notwithstanding the imperfect state of telescopes in those times, we still owe a great deal of our knowledge of the heavenly bodies to the observations that were made by those first telescopic observers, who made amends for the deficiencies of their instruments by their uncommon diligence and attention. It may, perhaps, be esteemed to be a mere matter of curiosity to search after the height of the lunar mountains. I grant that there are more necessary and more useful objects of inquiry in the science of astronomy; but when we consider that the knowledge of the construction of the Moon leads us insensibly to several consequences, which might not appear at first; such as the great probability, not to say almost absolute certainty, of her being inhabited, we shall soon agree, that these researches are far from being trifling. My reason for repeating observations that have been made by very good astronomers was not that I doubted either their veracity or diligence. The names of Galileo, Hevellus, Kircher, and several more, will always deserve to be mentioned with particular respect for the eminent services they have rendered to astronomy; but as we know that their instruments were far from being arrived to that degree of perfection we have now obtained, I thought it by no means improper or useless to repeat their observations on the lunar mountains, and to extend them to other parts of the Moon's visible hemisphere, and thereby to establish this theory on the firmest evidence of a survey taken by a very excellent instrument.
2. Astronomical Observations on the Periodical Star in Collo Ceti.
Read: 11 May 1780.
This remarkable star, we are told [Ferguson, Astronomy], "was first observed by David Fabricius, the 13th of August, 1596, who called it the Stella Mira, or wonderful star: which has been since found to appear and disappear, periodically, 7 times in 6 years, continuing in the greatest lustre for 15 days together, and it is never quite extinguished." My own observations on this wonderful star, are but few, yet sufficiently verify the surprising appearances that have been ascribed to it.
3. Astronomical Observations on the Rotation of the Planets around their Axes made with a View to determine whether the Earth's diurnal Motion is perfectly equable.
Read: 11 January 1781.
Sir, - The various motions of the planet we inhabit; the annual revolution in its orbit; the diurnal rotation round its axis; the menstrual motion round the common center of gravity of the moon and earth; the precession of the equinoctial points; the diminution of the obliquity of the ecliptic; the nutation of the earth's axis: in short, every one of the motions that arise from the actions of the sun, moon, and planets, combined with the spheroidical figure of the earth, and the projectile and rotatory motions first impressed upon it, have all been considered by astronomers, and their real and apparent inequalities investigated. And to the great honour of modem astronomers it must be confessed, that no science has ever made such considerable strides towards perfection in so short a time as astronomy has done since the invention of the telescope. There is one of the motions of the earth however which, it seems, has hitherto escaped the scrutiny of observers; I mean the diurnal rotation round its axis. The principal reason why this has not been looked into, is probably the difficulty of finding a proper standard to measure it by; since it is itself used as the standard by which we measure all the other motions. We have, indeed, no cause to suspect any very material periodical irregularity, either diurnal, menstrual, or annual; for the great perfection of our present time-pieces would have discovered any considerable deviation from that equability which we have hitherto ascribed to the diurnal motion of the earth. And yet, it is not perhaps altogether impossible but that inequalities may exist in this motion which, in an age where observations are carried to such a degree of refinement, may be of some consequence.
4. On the Periodical Star in Collo Ceti.
Read: 2 February 1781.
Last year I presented to this Society a Memorandum of the uncommon lustre of the periodical Star in Cello Ceti; It is somewhat remarkable that the succeeding Period should be distinguished by the very reverse of the former. The subject is so involved in obscurity that I shall attempt little more than to deliver my observations accompanied with a few conjectures, leaving it to future Observers to frame some plausible theory, when many succeeding periods may have furnished means to direct the thoughts in this pursuit. A star, (a Sun I should say,) perhaps surrounded with a system of Planets depending upon it, undergoes a change, which, were it to happen to our Sun, would probably be the total destruction of every living creature! What an amazing alteration from the first magnitude down to the 6th, 7th or 8th! But let me not take up a time in admiration which may perhaps be more philosophically employed in reciting plain matters of fact. The observations I have been able to make upon this wonderful star are this time fewer than I could wish to have made; yet are sufficient to deserve to be mentioned as they are so far connected with the former, that we may presume to conjecture the remarkable want of brightness in this period to be some natural consequence of the super-abundant light in that immediately preceding.
5. Account of a Comet.
Read: 26 April 1781.
On Tuesday the 13th of March, between ten and eleven in the evening, while I was examining the small stars in the neighbourhood of H Geminorum, I perceived one that appeared visibly larger than the rest; being struck with its uncommon magnitude, I compared it to H Geminorum and the small star in the quartile between Auriga and Gemini, and finding it so much larger than either of them, suspected it to be a comet. I was then engaged in a series of observations on the parallax of the fixed stars, which I hope soon to have the honour of laying before the Royal Society; and those observations requiring very high powers, I had ready at hand the several magnifiers of 227, 460, 932, 1536, 2010, &c. all which I have successfully used upon that occasion. The power I had on when I first saw the comet was 227. From experience I knew that the diameters of the fixed stars are not proportionally magnified with higher powers, as the planets are; therefore I now put on the powers of 460 and 932, and found the diameter of the comet increased in proportion to the power, as it ought to be, on a supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. The sequel has shown that my surmises were well founded, this proving to be the Comet we have lately observed.