Caroline Herschel as Observer

de Lalande J. Caroline , 12 July 1790, in The Herschel chronicle , by Lubbock Constance A. (Cambridge, 1933; hereafter Chronicle ), 251.

Letter of Nevil Maskelyne to Caroline, 6 July 1799, BL microfilm M/588(4).

Caroline Herschel's autobiographies , ed. by Hoskin Michael (Cambridge, 2003; hereafter: Autobiographies ), 47.

Letter of William to Caroline sent from Hanover, 22 August 1777: “Mama is very well and as I have represented things gives her consent to your staying in England as long as you and I please”, RAS MS Herschel W.1/8.

RAS MS W.5/12/1, 44. It has been said that William never made telescopes of Gregorian form but this is not so.

Marsh John , manuscript memoirs, ix, 753–4 [Cambridge University Library, Add MS 7757]. I am indebted to Kenneth James for this reference.

See ref. 3.

Autobiographies 66.

Autobiographies 71.

Autobiographies 71.

Caroline's observing books are preserved as RAS MS Herschel C.1/1.1–3, which are consecutively paginated and arranged in chronological order; and in what follows, unreferenced observations are to be found in these Books or in her surviving Journal 4, C.1/1.4. This information comes from a sheet in William's hand pasted in the front. Most exceptionally, Caroline makes a slip (30° for 3′) when copying the data onto p. 11.

Autobiographies 71.

In the Connoissance des temps for 1784, published in advance in 1781.

On William's early work on nebulae, see Hoskin Michael , “William Herschel's early investigations of nebulae: A reassessment”, Journal for the history of astronomy , x (1979), 165–76, reprinted in Hoskin Michael , Stellar astronomy: Historical studies (Chalfont St Giles, 1982), 125–36.

RAS MS Herschel W.2/1.5. In what follows, citations from William's observations are taken from his Journal, W.2/1, unless otherwise stated.

Herschel William , “Catalogue of double stars”, Philosophical transactions , lxxii (1782), 112–62.

Herschel William , “Catalogue of one thousand new nebulae and clusters of stars”, Philosophical transactions , lxxvi (1786), 457–99.

RAS MS Herschel W.4/1.4, f. 338.

Serio Foderà G. Indorato L. Nastasi P. , “G. B. Hodierna's observations of nebulae and his cosmology”, Journal for the history of astronomy , xvi (1985), 1–36, Table 5, 1.

RAS MS Herschel W.2/1.7, f.4.

19 November 1783, “My 3^d nebula is Mess 46^th”.

Caroline is credited with having discovered a nebula in Monoceros, but it is not near 19 Mon: Herschel William , “Catalogue of a second thousand of new nebulae and clusters of stars…”, Philosophical transactions , lxxix (1789), 212–55, VII.27.

One might have expected the string to be long enough to permit a sweep from the horizontal all the way to the vertical, and this is what William says in the description that follows; but Caroline speaks of having to stop “when the Screw was at an end” (p. 11).

Herschel William , “On the power of penetrating into space by telescopes”, Philosophical transactions , xc (1800), 49–85, p. 71. Cf. Herschel Caroline , “An account of a new comet”, ibid. , lxxvii (1787), 1–3.

The sweeper was located in the Historical Museum at Hanover by Margaret Bullard, who describes her discovery and transcribes Caroline's description and instructions in “My small Newtonian sweeper — Where is it now?”, Notes and records of the Royal Society , xlii (1988), 139–48. For the passage quoted, see pp. 146–7.

The wood of Brya Ebenus, a West Indian wood familiar to William for its use in the making of oboes, and much favoured by him for eyepieces.

Bullard Mrs ( op. cit. (ref. 25)) rightly corrects Hoskin and Warner's identification of the sketches of Caroline's instruments ( Hoskin Michael Warner Brian , “Caroline Herschel's comet sweepers”, Journal for the history of astronomy , xii (1981), 27–34), but is mistaken in thinking the sweeper was Herschelian.

In her letter of 2 August 1786 to Blagden announcing the discovery, Caroline expressly states her observations were made with a power of about 20 and a field of view of 2′ 12′, RAS MS C.1/3.1. Strangely, in her letter to Aubert written the same day, she says “I made these observations with my little Newtonian sweeper, and used a power of about 30: The field is about 1 ½ degree”, ibid. Writing two days later to Dietrich Herschel, she again says that she found the comet with the higher magnification, ibid. The details she gives in the letters to Blagden and to Aubert have much in common and there seems no way of reconciling what she says about the eyepieces she used.

In the letter to Blagden cited in the previous reference. Interestingly, in her observing book for 18 December 1783, Caroline speaks of sweeping “with a power of 15”.

“The apparatus on which it is mounted is contrived so as at present to confine the instrument to a meridional situation”, Herschel William , “Account of some observations tending to investigate the construction of the heavens”, Philosophical transactions , lxxiv (1784), 437–51, p. 437. The paper is dated April 1784. In the preface to his “Catalogue of one thousand new nebulae and clusters of stars” (ref. 17), William says that from the start the reflector had a gallery nine feet long, and that merely by walking from one end of the gallery to the other he could obtain a range in azimuth of as much as 30′. This is puzzling as the famous painting showing the reflector at Datchet has no gallery; instead the observer is seated in a chair. Furthermore, the apparatus is clearly designed to be rotated and there seems no reason why it should always face south.

RAS MS Herschel W.4/1.5, 448–50; Herschel , op. cit. (ref. 17), preface.

On the work of Goodricke and Edward Pigott, see Hoskin Michael , “Goodricke, Pigott and the quest for variable stars”, Journal for the history of astronomy , x (1979), 23–41; reprinted in Hoskin , Stellar astronomy (ref. 14), 37–55.

Pigott Nathaniel Herschel William , 17 June 1782, RAS MS Herschel W.1/13.P.43.

Observation of 23 July 1783.

Pigott Edward archives of the Royal Astronomical Society, Letter 60.

Bullard , op. cit. (ref. 25), 146.

7 Eql is several degrees from 3 and 4 Eql, whereas 3, 4 and 7 Peg form a tight triangle of stars. I am grateful to Arndt Latusseck for first suggesting that Caroline may have mistaken the constellation. Fortunately, Caroline also tells us that the object is “In the neck of Equuleus or head of Aquarius”, and Owen Gingerich points out that Caroline must have been using the Hevelius atlas, which is the only one that juxtaposes the head of Aquarius and the neck of Equuleus right on the stars 3, 4, and 7. It would have been entirely reasonable for Caroline to refer them as 3, 4, and 7 Equulei, for only by careful research would she have found that Flamsteed had in fact put these stars in Pegasus.

RAS MS Herschel W.2/1.7.

On this instrument see Bennett J. A. , “‘On the power of penetrating into space’: The telescopes of William Herschel”, Journal for the history of astronomy , vii (1976), 75–108, pp. 79–81. A generation on, this article remains the primary source for information on William's telescopes.

On this episode, see Autobiographies 75. On its background, see Hoskin Michael , The Herschel partnership (Cambridge, 2003; hereafter: Partnership ), 68–69.

Herschel William , op. cit. (ref. 17), Preface.

Ibid. .

For eyewitness accounts of how she operated as William's amanuensis, see Ashworth William B. Jr , “Faujas-de-Saint-Fond visits the Herschels at Datchet”, Journal for the history of astronomy , xxxiv (2003), 321–4, and the letter from Magellan to Bode published in Bode's Jahrbuch for 1788 and quoted in Chronicle , 138–9.

See her note on p. 100 of RAS MS Herschel C.1/1.3.

Autobiographies , 83–91.

Caroline to Charles Blagden, 2 August 1786 (ref. 27).

Autobiographies 89.

Caroline to Charles Blagden, 2 August 1786 (ref. 27).

Caroline to Alexander Aubert, 2 August 1786 (ref. 27).

See ref. 27.

Chronicle 156.

Chronicle 169.

See for example Caroline de Lalande J. , 12 September 1790, Memoir 91.

References to the time by Alexander's clock, and the correction it required that evening, are frequent in Caroline's observing books. On the journeyman clock, known in the family as “the monkey clock”, see Hoskin Michael , “Alexander Herschel: The forgotten partner”, Journal for the history of astronomy , xxxv (2004), 387–420, pp. 401–2. The Shelton timepiece still keeps good time.

RAS MS Herschel C.1/1.4.

Charles Henry Sir Englefield had recently published Tables of the apparent places of the comet of 1661 … whose return is expected in 1789 (London, 1788). I thank Brian Marsden, and Martin Mobberley of the Society for the History of Astronomy (U.K.), for their help with the possible orbit of the returning comet. William in a letter of 8 January 1789 to the Earl of Salisbury states that Caroline found her second comet while on the lookout for the predicted return, Chronicle 247. In Partnership 105, it is wrongly stated that Caroline's comet had previously been seen by Messier, following Hughes David W. , “Caroline Lucretia Herschel — comet huntress”, Journal of the British Astronomical Association , cix (1999), 78–85, p. 80.

Information kindly supplied by Brian Marsden. For Caroline's letter to Maskelyne announcing the discovery, see Chronicle 245.

Marsden Brian , personal comm., 2005.

Maskelyne Nevil William , 10 January 1789, RAS MS Herschel W.1/13.M.37.

Herschel William , “On the power of penetrating into space by telescopes”, Philosophical transactions , (1800), 49–85, p. 71.

On this see Dreyer J. L. E. , The scientific papers of Sir William Herschel (London, 1912), i, p. xxxviii. William's brief paper, “An account of three volcanos in the Moon”, had appeared in Philosophical transactions , lxxvii (1787), 229–32. Caroline looked again for luminous spots on the Moon on 19 and 20 March 1790, but without success.

As we shall see, Caroline was invariably to use the large sweeper when examining the Moon for possible volcanoes.

Chronicle 248. Nevil Maskelyne was to send her a lamp the following autumn, Maskelyne to William, RAS MS Herschel W.1/13.M.49.

On this see Smith Robert , A compleat system of opticks (Cambridge, 1738). I thank Randall Brooks for his help with Caroline's calculations with the ‘rhumboides’.

Nevil Maskelyne to William, 29 August 1791, RAS MS W.1/13.M.48.

Nevil Maskelyne to William, 23 July 1791, RAS MS W.1/13.M.47.

RAS MS Herschel C.1/1.2, end matter.

Chronicle 252.

RAS MS Herschel C.1/1.4.

Nevil Maskelyne to Nathaniel Pigott, 6 December 1793, Nathaniel Pigott archives of the Royal Astronomical Society.

On 25 April 1792.

Bullard , op. cit. (ref. 25), 146.

This impression is confirmed by what William says in “Miscellaneous observations”, Philosophical transactions , lxxxii (1792), 23–27.

Wollaston Francis , A specimen of a general astronomical catalogue, arranged in zones of North Polar Distance (London, 1789), and therefore in exactly the format that Caroline herself used.

On 12 May 1793. Caroline , “tho' I never had any practice with that instrument”, made her own measurement, which was just one minute larger than William's.

RAS MS C.1/1.4.

RAS MS C.1/1.4.

Information from Brian Marsden.

Entry for 20 August 1794.

Herschel Caroline , “Account of the discovery of a new comet”, Philosophical transactions , lxxxvi (1796), 131–2.

Marsden Brian informs me that he has a report that the comet was later seen by other observers, on 11 and 14 November, but he is not convinced that the report is true.

BL microfilm M/588(4). In a letter to Caroline of 24 October 1835, John Herschel speaks of a comet that is “Encke's (yours)”, BL Egerton 3762.

Nevil Maskelyne to Caroline, 27 December 1788, RAS MS Herschel C.1/3.2.

Partnership 109.

“1797 in October I went to lodge & Board with one of my Brother's workmen (Sprat) whose wife was to attend on me”, from “Extracts from a daybook kept during the years 1797 & 1821”, BL microfilm M/588(4). In later life she destroyed her personal records for the unhappy decade following William's marriage in 1788, and we rely on hints given retrospectively for what little we know of the reason for her move into lodgings. In incomplete autobiographical notes concerning John's childhood she says: “But after the above mentioned October [1797] we were not so frequently together, for I was obliged to exchange my habitation to another part of Slough …”, BL microfilm M/588(4). To John Herschel's wife Margaret on 6 September 1833 she remarks that when John was five she “came to be detached from the family circle”, BL Egerton 3761. To John himself she wrote on 4 May 1843 to say that at the end of 1789 “I was severed from the Family but occasionally passed still as a Link of the same”, BL Egerton 3762.

The move was disastrous. Writing to Margaret in February 1840, she says that “… for the last 24 years of my living in England, it was amongst beings of whom I was affraid”, and adds that in those years “I was obliged to change my habitation no less than 7 times, which was always attended with useless expenses, and what was still more precious, loss of time”, BL Egerton 3762. For these moves and something of the vexations they caused, see Partnership , 115–16. Constance Lubbock, granddaughter of William, suggests ( Chronicle 296) that she moved because of “the accumulation of books and instruments” but this is hardly credible. One suspects that either William or his gentle wife Mary made some unguarded remark to the effect that Caroline was indebted to them for a roof over her head, and that this revived her lifelong resentment at her dependence on her brothers. Now at last she could pay for her own lodgings. The fact that she took rooms with one of William's workmen only adds to the suspicion that her departure was precipitate.

BL microfilm M/588(4).

Nevil Maskelyne to Caroline, 22 April 1790, RAS MS Herschel C.1/3.4.

We know it was the small sweeper because she specifies the field of view, namely 2′ 12′.

Again, we know it was the small sweeper that Caroline used because she specifies that the comet filled the field of view of the eyepiece “about 3 ½ times = 7′ 3/4”.

Packing lists for the voyages are now in the University of Texas at Austin, information courtesy of Brian Warner.

“My nephew did not wish my sending it to Slough”, BL microfilm M/588(4).

Hoskin Michael , “Caroline Herschel's ‘small’ sweeper”, Journal for the history of astronomy , xxxvi (2005), 28–30, which contains a colour photograph of the surviving optics.

His third catalogue in fact contains not 500 but 507 stars. See Hoskin Michael , “William Herschel's sweeps for nebulae”, Journal for the history of astronomy , xxxvi (2005), 230.

Herschel J. F. W. , “Catalogue of nebulae and clusters of stars”, Philosophical transactions , 1864, 1–137.

Most notably in his “Astronomical observations relating to the construction of the heavens”, Philosophical transactions , ci (1811), 269–336, p. 271.

Hughes estimates the limiting magnitude of this sweeper as 12.0, and that of its larger successor, 13.7. See Hughes , op. cit. (ref. 55), 78.

For further information, see gchbryant.tripod.com/Articles/Caroline0597.htm.

Autobiographies , 71–72. On 14 May 1784 Caroline found another cluster which she later said was her “number 16” (p. 100). Earlier, on 23 February, she had found a cluster she reckoned to be about 1 ¼′ S following κ Cas (and which she viewed again on 8 and 11 March). This was evidently her number 15, so she was keeping a careful list of her discoveries.

As remarked by Dreyer , op. cit. (ref. 60), i, p. xliv.

I thank Owen Gingerich for this identification.

See ref. 36.

This cartoon was published in Olson Roberta J. M. Passachoff Jay M. , Fire in the sky (Cambridge, 1998).