430 



NA TURE 



\_March lo, 1881 



course of time, I took up astronomy, I determined to 

 accept nothing on faith, but to see with my own eyes 

 everything which others had seen before me. Having 

 already some knowledge of the science of optics, 1 

 resolved to manufacture my own telescopes, and after 

 many continuous, determined trials, I finally succeeded 

 in completing a so-called Newtonian instrument, sevtn 

 feet in length. From this I advanced to one of ten feet, 

 and at last to one of twenty, for I had fully made up my 

 mind to carry on the improvement of my telescopes as 

 far as it could possibly be done." A very good twenty- 

 feet reflector was finished in 1783, but the celebrated 

 forty-feet instrument was not commenced until 17S5. 

 Herschel tells us in his description of the latter telescope 

 that in all he made "not less than 200 7-feet, 150 lo-fcet, 

 and about So 20-feet mirrors, not to mention those of the 

 Gregorian form, or of the construction of Dr. Smith's 

 reflecting microscope," of which he also made a great 

 number. 



In or about 1779 Herschel removed to 19, New King 

 Street, which was his last change of residence at Bath, 

 and it was at this house that the planet Uranus was dis- 

 covered. His first astronomical paper, on the variable 

 star Mira Ceti, was written from thence, and appeared in 

 the Philosophical Transactions for 1780: he had pre- 

 viously contributed a paper (his first publication) to the 

 Ladies' Diary in 1779, in answer to a prize question pro- 

 posed by Landen, viz. " the length, tension, and weight of 

 a musical string being given, it is required to find how 

 many vibrations it will make in a given time, when a 

 small given weight is fastened to its middle, and vibrates 

 with it." In the same volume of the Phil. Trans, lie 

 published observations relating to the mountains in the 

 moon ; at this time and subsequently he measured the 

 heights of about 100, on three different methods. Most 

 of these measures were xievtr printed, and as Prof. Holden 

 remarks at this date they would probably be of no material 

 service to science. 



His next paper presented to the Royal Society on 

 January 11, 17S1, is entitled "Astronomical Observations 

 on the rotation of the Planets round their Axes, made 

 with a view to determine whether the Earth's Diurnal 

 Motion is perfectly equable," a paper which Prof. Holden 

 views as afibrding the first obvious proof of the truth of 

 the statement made by Herschel thirty years later, when 

 he said, " A knowledge of the construction of the heavens 

 has always been the ultimate object of my observations." 

 It marks too an advance in practical astronomy : not 

 only are the results given, but careful estimates of the 

 errors to which they may be liable is made, with a 

 discussion of the source of such errors. 



On March 13 following Herschel made his great dis- 

 covery of the planet Uranus, that Georgium-Sidits, as it 

 was his wish it should be called, which made his name at 

 once familiar throughout Europe. The discovery was 

 announced in a paper communicated to the Royal Society 

 on April 26 by Dr. Watson of Bath, an intimate friend 

 of Herschel's, and strange as it may now appear to us, 

 it is entitled "Account of a Comet." His own words 

 referring to the circumstances of the discovery are as fol- 

 lows :— " 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, .... and those observations requiring very 

 high powers, I had ready at hand several magnifiers of 

 227, 460, 932, 1536, 2010, &c., all of which I have suc- 

 cessfully used upon that occasion. The power I had on 

 when I first saw the comet was 227. From e-xperience I 

 knew that the diameters of the fixed stars are not pro- 

 portionally 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 propor- 

 tion 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 observa- 

 tions given in this paper extend to April 19, and Herschel 

 adds he was " happy to surrender it to the care of the 

 Astronomer- Royal " (Dr. Maskelyne) and others as soon as 

 he found they had begun their observations upon it : so 

 little idea had he six weeks after he first glimpsed the 

 object of the great discovery he had made. 



It is certain that at the date of this discovery the name 

 of Herschel was unknown to the principal astronomers 

 on the Continent, and it is almost ludicrous to read of 

 the various guesses that were made respecting it. Prof. 

 Holden transcribes the amusing passage from Bode's 

 account of the discovery of Uranus ; " In the Gazette 

 Littcraire of June, 1 781, this worthy man is called 

 MerSTHEL ; in Julius' Journal Encyclopi'dique, HerT- 

 SCHEL ; in a letter from Mr. Maskelyne to M. Messier, 

 Herthel ; in another letter of Maskelyne's to Herr Mayer 

 at Manheim, HerrSCHELL [doubtless mis-readings] ; M. 

 Darquier calls him Hermstel. What may his name be .' 

 He must have been born a German." In the first notice 

 of the discovery in the Connaissance des Temps he is called 



HOROCHELLE. 



The telescope which Herschel was using on the evening 

 of March 13, 1781, was that with which his second review 

 of the heavens was made, a reflector' of 85-2 inches focus, 

 6'2 inches aperture, and power, 227. This survey, he 

 writes in 1783, "extended to all the stars of Harris's maps 

 and the telescopic ones near them, as far as the eighth mag- 

 nitude. The catalogue of double-stars and the discovery 

 of the Georgium Sidus were the results of that review." 



Arago says if Herschel had directed his telescope towards 

 the constellation Gemini eleven days earlier (March 2 

 instead of March 13) the proper motion of the planet 

 would have escaped him, for the planet was on the and 

 near one of its stationary points, and adds, "On voit 

 par cette remarque Ji quoi peuvent tener les plus grandes 

 ddcouvertes astronomiques." This implies a total mis- 

 conception of the case : as Prof. Holden remarks :— "The 



' When Sir John Herschel contemplated presenting one of his father's 

 7-feet telescopes to the Royal Astronomical Society. Caroline HerSI^hel 

 wrote: "Its only being painted deal was because i_t_ should look hke the 

 one with which the Georgium Sidus was discovered." 



