“We may also have surmised nebulae to be no other than clusters of stars disguised by their very great distance”, HerschelWilliam, “Astronomical observations relating to the construction of the heavens …”, Philosophical transactions, ci (1811) [hereafter: 1811 paper], 269–336, p. 270; “… clusters of stars in disguise, on account of their being so deeply immersed in space”, HerschelWilliam, “Astronomical observations and experiments, selected for the purpose of ascertaining the relative distances of clusters of stars …”, Philosophical transactions, cviii (1818) [hereafter: 1818 paper], 429–70, p. 466.
2.
HoskinMichael, “William Herschel and the nebulae, Part 1: 1774–1784”, Journal for the history of astronomy, xlii (2011), 177–92, p. 186.
3.
“A very remarkable circumstance attending the nebulae and clusters of stars is, that they are arranged into strata…. It is probable enough, that they may surround the whole apparent sphere of the heavens, not unlike the milky way, which undoubtedly is nothing but a stratum of fixed stars”, HerschelWilliam, “Account of some observations tending to investigate the construction of the heavens”, Philosophical transactions, lxxiv (1784) [hereafter: 1784 paper], 437–51, p. 442. Much of the rest of the paper is concerned with these strata.
4.
HerschelWilliam, “On the construction of the heavens”, Philosophical transactions, lxxv (1785) [hereafter: 1785 paper], 213–66.
5.
Ibid., 216.
6.
HoskinMichael, “Newton, Providence and the universe of stars”, Journal for the history of astronomy, viii (1977), 77–101.
7.
Herschel, 1785 paper, 217. Cf. HerschelWilliam, “Catalogue of 55 new nebulae … with remarks on the construction of the heavens”, Philosophical transactions, xcii (1802) [hereafter: 1802 paper], 477–528, p. 479: “… the stars we consider as insulated are also surrounded by a magnificent collection of innumerable stars, called the milky-way, which must occasion a very powerful balance of opposite attractions, to hold the intermediate stars in a state of rest”.
8.
Herschel, 1785 paper, 216.
9.
Ibid., 217.
10.
Ibid., 217.
11.
Ibid., 263–6.
12.
Royal Astronomical Society Herschel Archive (hereafter: RAS) W.2/1.2, f. 231.
13.
For example, in 1783 on 30 July, 25 August, 20 September, 17 and 23 October and 14 November, and in 1784 on 16 and 28 June, 15 July and 12 November. RAS W.4/1.5, W.4/1.7, W.2/3.2, W.2/3.3.
14.
Herschel, 1785 paper, 265–6.
15.
RAS W.1/1, 129, letter to Lalande, 17 March 1785: “… des corps celèstes dont nous n'avons pas encore d'idée bien claire & qui sont peut-être d'un genre tout à fait different de ce que nous connoissons dans les cieux”.
16.
For example, on 27 November 1787, Herschel showed his visitors the planetary nebula H.IV.18: “Messrs Cassini, Mechain Le Seure & Carochet saw this nebula, and the moon being absent, it appeared in its usual planetary view; these Gentlemen saw it very well and admired it as a great curiosity. Mr Cassini observed that a very small fixt star nf the nebula appeared not unlike a sattelite to it” (RAS W.2/3.7). Planetary nebulae were also shown to William Watson and a Mr Marsden on 11 March 1788, to Lord Palmerston on 3 August 1788, to Lalande on 5 August 1788, he “having never before seen a planetary one”, to Edward Pigott on 6 August 1788, and to the Abbé Ximenes on 13 April 1789, ibid.
17.
As he had explained at length in the 1784 paper, 443–5. There is a minor complication. Because we see the Milky Way as bifurcated, our Galaxy, “the stupendous sidereal system we inhabit”, consists of an “extensive stratum and its secondary branch”, Herschel, 1785 paper, 244.
18.
Herschel, 1785 paper, 244.
19.
Herschel, 1785 paper, 248.
20.
Herschel, 1785 paper, 255.
21.
Herschel, 1785 paper, 255.
22.
Herschel, 1785 paper, 256.
23.
Herschel, 1784 paper, 445.
24.
Herschel, 1785 paper, 250–4.
25.
“By these observations it appears that the utmost stretch of the space-penetrating power of the 20 feet telescope could not fathom the Profundity of the milky way … [the 40 feet] would then leave us again in the same uncertainty as the 20 feet telescope”, Herschel, 1817 paper, 327.
26.
Herschel, 1785 paper, 244: “We inhabit the planet of a star belonging to a compound nebula of the third form.” Cf. ref. 17 above.
27.
Herschel, 1785 paper, 260. He supposes the Andromeda Nebula to be “the united lustre of millions of stars”, ibid., 249.
28.
Herschel, 1785 paper, 255.
29.
HerschelWilliam, “Catalogue of a second thousand of new nebulae and clusters of stars; with a few introductory remarks on the construction of the heavens”, Philosophical transactions, lxxix (1789) [hereafter: 1789 paper], 212–55.
30.
Herschel, 1789 paper, 213, 214.
31.
Herschel, 1789 paper, 214.
32.
“… the component clustering stars [of a globular cluster] do not, perhaps, exceed each other in magnitude more than in some such proportion as one full-grown plant of a certain species may exceed another full-grown plant of the same species”, Herschel, 1789 paper, 216; “This variety of size [that we encounter among] different spherical clusters, I am however inclined to believe, may not go farther than the difference in size, found among the individuals belonging to the same species of plants, or animals …”, ibid., 224.
33.
As we shall see, in 1811 and 1814 he would arrange innumerable nebulae and clusters from his catalogues in sequence, to imitate “the annual description of the human figure, were it given from the birth of a child till he comes to be a man in his prime”, Herschel, 1811 paper, 271. In 1817 Herschel assumes that “one with another the stars are of a certain physical generic size and brightness, still allowing that all such deviations may exist, as generally take place among the individuals belonging to the same species”, 1817 paper, 309.
34.
Herschel, 1789 paper, 219.
35.
Herschel, 1811 paper, 284: “Instead of inquiring after the nature of the cause of the condensation of nebulous matter, it would indeed be sufficient for the present purpose to call it merely a condensing principle; but … why should we not look up to the universal gravitation of matter as the cause of every condensation, accumulation, compression, and concentration of the nebulous matter?”.
36.
Herschel, 1789 paper, 221.
37.
Herschel, 1789 paper, 222.
38.
William Watson to Herschel, 12 May 1789, W.1/13.W.55. From the covering letter I quote the words Watson originally wrote, as better representing his opinion.
HerschelWilliam, “On nebulous stars, properly so called”, Philosophical transactions, lxxxi (1791) [hereafter: 1791 paper], 71–88, p. 78. Wolfgang Steinicke (private communication) comments that Herschel might well have said the same of two ‘planetary nebulae’ in which the central star is prominent and which he encountered long before the object that provoked his change of mind: NGC 2170 (IV.19, but not a planetary nebula in the modern sense), which he viewed on 16 October 1784 and which he cites in the 1791 paper, and NGC 2392 (IV.45), which he viewed on 17 January 1787. Cf. Wolfgang Steinicke, Observing and cataloguing nebulae and clusters (Cambridge, 2010), 40.
47.
Herschel, 1791 paper, 86.
48.
Cf. Herschel, 1811 paper, 318: “… perhaps in progress of time these nebulae which are already in such a state of compression, may be still farther condensed so as actually to become stars”.
49.
Herschel, 1791 paper, 85.
50.
Herschel, 1791 paper, 87.
51.
Herschel, 1791 paper, 87.
52.
Herschel, 1802 paper.
53.
“Now, should we imagine [the Galaxy] to be an irregular ring of stars, in the center nearly of which we must then suppose the sun to be placed, it will appear not a little extraordinary, that the sun, being a fixed star like those which compose this imagined ring, should just be in the center of such a multitude of celestial bodies, without any apparent reason for this singular distinction …”, Herschel, 1784 paper, 445.
54.
HerschelWilliam, “An account of the changes that have happened, during the last twenty-five years, in the relative situation of double stars …”, Philosophical transactions, xciii (1803), 339–82, and “Continuation of an account …”, Philosophical transactions, xciv (1804), 1804–84.
55.
“… probably, we can only look for solar systems among isolated stars”, 1802 paper, 480.
56.
Herschel, 1802 paper, 495.
57.
“when we examine the milky way … this supposed equality of scattering must be given up” (Herschel, 1811 paper, 270); “it is, however, evident that, if ever it consisted of equally scattered stars, it does so no longer” (HerschelWilliam, “Astronomical observations relating to the sidereal part of the heavens”, Philosophical transactions, civ (1814) [hereafter: 1814 paper], 248–84, p. 282); his gages of the 1780s, he says in 1817, “relate more immediately to the scattering of stars” than to distance (William Herschel, “Astronomical observations and experiments tending to investigate the local arrangement of the celestial bodies in space”, Philosophical transactions, cvii (1817) [hereafter: 1817 paper], 302–31, p. 25.
“… its nature remains mysterious”, Herschel, 1814 paper, 260.
61.
Herschel, 1818 paper, 453.
62.
Herschel, 1802 paper, 496.
63.
Herschel, 1802 paper, 497.
64.
Herschel, 1811 paper and 1814 paper.
65.
Herschel, 1811 paper, 271.
66.
Herschel, 1811 paper, 331.
67.
Herschel, 1814 paper, 248.
68.
Herschel, 1814 paper, 253. Cf. p. 259, where he writes: “We can only hint, that every nebulosity which is carried into the region of a small patch of stars will probably be gradually arrested and absorbed by them, and that thus the growth of stars may be continued”.
69.
Herschel, 1814 paper, 280.
70.
Herschel, 1814 paper, 278.
71.
Herschel, 1814 paper, 248.
72.
Herschel, 1811 paper, 272–3.
73.
Herschel, 1802 paper, section IX.
74.
Herschel, 1811 paper, 306.
75.
Herschel, 1811 paper, 277.
76.
Herschel, 1811 paper, 280.
77.
Herschel, 1811 paper, 291–2.
78.
Herschel, 1814 paper, 267.
79.
Herschel, 1811 paper, 312.
80.
Herschel, 1811 paper, 319.
81.
RAS W.7/15, 1798 tour.
82.
Herschel, 1802 paper, 498–9. In September 1813 Herschel met the poet Thomas Campbell and told him the same. Campbell wrote to a friend, “I really and unfeignedly felt at the moment as if I had been conversing with a supernatural intelligence” (LubbockConstance A., The Herschel chronicle (Cambridge, 1933), 336, citing Life and letters of Th. Campbell, ed. by BeattieWilliam (London, 1849)).
83.
Herschel, 1811 paper, 302.
84.
Herschel, 1811 paper, 287.
85.
Herschel, 1814 paper, 283.
86.
Herschel, 1814 paper, 283–4.
87.
“Address …”, Memoirs of the Astronomical Society of London, i (1822–25), 4.
