William Herschel and the Prehistory of Stellar Spectroscopy

RAS MS Herschel W.4/1.3.

Howse Derek , Greenwich Observatory , iii: The buildings and instruments (London, 1975), 114–15.

Ibid. .

RAS MS Herschel W.4/1.3.

Ibid. ε Boo consists of an orange star, mag. 2.5, with a blue companion, mag. 4.6, and the appearance of the pair is so striking as to have earned the alternative name Pulcherrima (“Most beautiful”). α Her is formed of a red giant (variable mag. between 3 and 4) with a blue-green companion (mag. 5.4). ζ UMa, or Mizar, was the first double star to be discovered telescopically, by Riccioli in 1650; the components have mag. 2.2 and 4.0 respectively.

RAS MS Herschel W.4/1.3. γ And, or Almaak, has an orange component of mag. 2.3 and a blue of mag. 4.8 (and a third, fainter star not seen by Herschel).

RAS MS Herschel W.6/9.

No. 11, on electrifying a speculum and passing a shock through it, matches Herschel's paper on “Electrical experiments” read to the Bath Society on 7 April 1780 ( Dreyer J. L. E. (ed.), The scientific papers of Sir William Herschel (London, 1912), i, p. lxxx), as does no. 33 ( ibid. , p. lxxix). No. 26, “To find what stars have changed their notation since Bayer's Notation”, clearly belongs to Herschel's apprenticeship in astronomy. In no. 26 he mentions “Ld Mahon's experiments”, a reference to Principles of electricity (1779) by Charles Stanhope Lord Mahon , who became Earl Stanhope in 1786, and so the entry is presumably no later than this date. Interestingly, in no. 5 he proposes “To examine whether a large heavy body approaching to a passing ray [of light] will show the effects of gravity”.

On Courtivron see the article by McKeon Robert M. in Dictionary of scientific biography. .

Melvill Thomas , “A letter … with a discourse concerning the cause of the different refrangibility of the rays of light”, Philosophical transactions , xlviii/1 (1753), 261–8.

On Melvill see the article by North J. D. in Dictionary of scientific biography. .

Melvill , op. cit. , 267–8.

His untitled paper immediately follows that of Melvill.

Echoes of Melvill are also to be found in entries 109 and 110: “109. To consider the supposition of the particles [of light] differing in size or density. 110. The red rays may be the smallest and still the heaviest, or most dense.”.

Herschel's acute analysis of his careful observations was to have applications in other branches of astronomy, e.g. in the precise determination of declinations with meridian telescopes, which require corrections for atmospheric refraction and dispersion. Airy G. B. devised an ingenious eyepiece with a tilting eyelens to correct for the latter, see “On the eyepiece for correction of atmospheric dispersion”, Monthly notices of the Royal Astronomical Society , xxx (1870), 57–59.

RAS MS Herschel W.4/1.3, cf. W.2/1.5.

On 12 September 1793 a similar caution saved him from error. He found a lunar mountain was “strongly tinged with prismatic colours, which might occasion a mistake as no other part of the moon is tinged with the same. However, on putting it to the opposite field of view it is still tinged with prismatic colours but their order is inverted; which is an evident proof that this appearance arises from the eye glass”, RAS MS Herschel W.2/1.5.

RAS MS Herschel W.4/1.4. Herschel published the observation in 1805, see Dreyer, op. cit. (ref. 8), ii, 304.

Collinson writes from Southgate, Middlesex, which is some 8 miles north of central London, but nothing else is known of him. Apparently this was by no means the only occasion on which Collinson pressed Herschel to study stellar spectra, for in a letter of 20 November 1795 (RAS MS Herschel W.1/13.C.20) he reassures him: “Fear not, my worthy friend, that I am again to persecute you with the Old Story, relative to the prismatic Colours of the Stars.”.

Collinson to Herschel, RAS MS Herschel W.1/13.C.18.

Collinson to Herschel, RAS MS Herschel W.1/13.C.19. Nor was Collinson the only friend to urge Herschel to study stellar spectra; his confidant William Watson wrote to him on 31 August 1783 to ask, “Have you done any thing further with respect to the prismatic Colours of the Stars?” (W.1/13.W.28).

Garnet stars fascinated Herschel to the end of his days. In “Astronomical observations relating to the sidereal part of the heavens”, Philosophical transactions , civ (1814), 248–84, p. 264, see Dreyer, op. cit. (ref. 8), ii, 529, he mentions that “In my sweeps are also recorded the places of 9 deep garnet, 5 bright garnet, and 10 red coloured stars…”.

RAS MS Herschel W.4/1.4.

Ibid. .

Wilson to Herschel, RAS MS Herschel W.1/13.W.95.

In Sweep 25, RAS MS Herschel W.2/1.4.

Herschel to Wilson, RAS MS Herschel W.1/1, 99–100.

Vince to Herschel, 10 January 1784, RAS MS Herschel W.1/13.V.2. Vince is referring to John Michell, “On the means of discovering the distance, magnitude, &c. of the fixed stars …”, Philosophical transactions , lxxiv (1784), 35–57.

Herschel to Vince, 15, RAS MS Herschel W.1/1, 93. Herschel had in fact observed a lunar occultation of the star Atlas in the Pleiades on 9 February 1783 and noticed no colour change: “Atlas went not at once but shewed an intermediate state during which time it was dimmer but not smaller than before”, RAS MS Herschel W.2/1.5.

“Eclipses of Jupiters Satellites”, RAS MS Herschel W.3/1.7.

RAS MS Herschel W.2/3.4.

RAS MS Herschel W.2/2.5. Herschel later published the observations in “Astronomical observations relating to the sidereal part of the heavens” (ref. 22), 264, see Dreyer , op. cit. (ref. 8), ii, 529.

Footnote by D. Dewhirst W. Hoskin Michael A. , William Herschel and the construction of the heavens (London, 1963), 159.