nebulae may be ‘island universes’ outside the Milky Way, thereby hugely increasing the sense of the actual size of the cosmos. Among these was the beautiful nebula in Andromeda, ‘faintly red’ at the centre. By 1785 his nebulae count had risen to well over 900. They appeared ‘equally extensive with that which we inhabit [the Milky Way]…yet all separate from each other by a very considerable distance’.186 He picked out at least ten ‘compound nebulae’ which he considered larger and more developed than the Milky Way, and imagined the star-cluster view of our own galaxies from theirs. ‘The inhabitants of the planets that attend the stars that compose them must likewise perceive the same phenomena. For which reason they may also be called Milky Ways by way of distinction.’187
As Kant had speculated, the cosmos might be infinite, whatever that might mean. Though Herschel’s estimates of cosmological distances were much too small by modern calculation, they were outlandishly, even terrifyingly, vast by contemporary standards. Beyond the visible parts of our own Milky Way, he estimated that a huge surrounding ‘vacancy’ of deep space existed, ‘not less than 6 or 8 thousand times the distance of Sirius’. He admitted that these were ‘very coarse estimates’. The implications seemed clear, though they were cautiously expressed in his paper: ‘This is amply sufficient to make our own nebula a detached one. It is true, that it would not be consistent confidently to affirm that we were an Island Universe unless we had actually found ourselves everywhere bounded by the ocean…A telescope with a much larger aperture than my present one [twelve inches], grasping together a greater quantity of light, and thereby enabling us to see further into space, will be the surest means of completing and establishing the argument.’188
The dramatic implications of these ideas were soon picked up by journalists and popularisers. The following year Bonnycastle assessed the situation in the first edition of his Introduction to Astronomy: ‘Mr Herschel is of opinion that the starry heaven is replete with these nebulae, and that each of them is a distinct and separate system, independent of the rest. The Milky Way he supposes to be that particular nebula in which our sun is placed; and in order to account for the appearance it exhibits, he supposes its figure to be much more extended towards the apparent zone of illumination than in any other direction…These are certainly grand ideas, and whether true or not, do honour to the mind that conceived them.’189
Also contained in Herschel’s revolutionary paper of 1785 were the seeds of a new, long-term project. He was planning the building of a monster forty-foot telescope, with a four-foot mirror. This would be the biggest and most powerful reflector in the world. With this he believed he could resolve once and for all the problem of the nebulae-whether they were other galaxies far beyond the Milky Way, or merely gas clouds within it. He would also have a better chance of establishing the true distance of the stars, through the measurement of stellar parallax. Above all he believed he would be able to understand how the stars were created, and whether the whole universe was changing or evolving according to some definite law or plan. Finally, he believed he might establish if there were observable signs of extraterrestrial life, a discovery which would have enormous impact on philosophical and even theological beliefs.
There was one other small, but revolutionary, departure in his 1785 paper. For the first time William Herschel carefully credited Caroline in print with a small ‘associate nebula’ in Andromeda. It was a previously unknown cluster ‘which my Sister discovered on August 27 1783 with a Newtonian 2 foot sweeper’. It was not in Messier’s annual catalogue La Connaissance des Temps, so this was Caroline Herschel’s first new addition to the universe.190
♣ Caroline eventually wrote out two versions of this memoir, the first in summer 1821, when she was seventy, and the second in 1840. She also destroyed two sections of the original record which she did not want read by other family members. A composite version was edited by her great-niece, Mrs John Herschel, and published by Murray in 1769. The manuscript still exists in the private collection of John Herschel-Shorland. The individual Memoirs have been meticulously published by Michael Hoskin, as Caroline Herschel’s Autobiographies (2003). William wrote a ‘Memorandum of my Life’ when he was nearly sixty, but this was a sort of professional CV for fellow scientists, comparatively short and characteristically reserved (Herschel, Scientific Papers 1, p.xiii). For full details see the Bibliography.
♣ Three of William Herschel’s works are currently available on CD. They are his Oboe Concertos in C major and E-flat major, and his Chamber Symphony in F major (Newport Classics, Rhode Island, USA, 1995). They are notable for their light musical touch and fine, sprightly melodic lines, sometimes with a certain melancholy in the slower passages. The rapid, complex orchestration around the solo oboe in the concertos is handled with great confidence, and suggests Herschel’s ability to manage patterns and counterpoint. This was a conceptual skill which he seemed to transfer (visually) to the patterning of stars and constellations. He moved from earthly music to the music of the spheres.
♣ A typical brass eighteenth-century orrery showed the sequence of six known planets: Mercury, Venus, Earth, Mars, Jupiter (with moons) and Saturn (with rings) orbiting around a central sun (sometimes operated by clockwork and illuminated by candles). Flamsteed showed all constellations-such as Herschel’s early favourites Orion, Andromeda and Taurus-against mythological engravings of their signs: the Hunter, the Goddess, the Bull. His Atlas Coelestis catalogued 3,000 stars; the modern Hubble telescope has identified some nineteen million. But the presentation of the night sky as a curved dome of mythological constellations is still quite usual, as for instance in the magnificently restored curved ceiling of Grand Central Station, New York.
♣ The use of horse-dung moulds for casting metal mirrors continued well into the twentieth century, with the 101-inch mirror of the Mount Wilson telescope in California, cast in Paris in 1920 and eventually used by Edwin Hubble to confirm Herschel’s theories about the nature and distance of galaxies in 1922. See Gale Christianson, Edwin Hubble: Mariner of the Nebulae (1995). Precision was never easy to obtain: the mirror of the modern orbiting Hubble Space Telescope was found to be two micrometres too flat at the edges, an error which cost $1.5 billion to correct in 1992.
♣ In describing the rebel angel’s enormous glowing shield, Milton contrives in Paradise Lost a beautiful reference to Galileo’s refractor telescope and the view he achieved of the moon.
…The broad circumference
Hung on his shoulders like the Moon, whose orb Through optic glass the Tuscan artist views At evening from the top of Fiesole. Or in Val d’Arno, to descry new lands, Rivers, or mountains in her spotty globe.
(Paradise Lost, Book I, lines 288-. See also Book III, lines 589-, and Book 5, 262-)
Milton here includes Galileo’s confirmation of an imperfect, ‘spotty’ globe, as described in his famous treatise The Starry Messenger (1610). His observations of rugged lunar mountains and irregular craters proved that not all celestial objects were perfect, and so the theologians were wrong about the nature of God’s creation (as well as about the movement of the earth around the sun). More subtly, Milton puts forward the notion of the moon as the earth’s cosmic shield, battered by many warlike blows from meteors. A modern poet might assign that task to Jupiter. As a young man Milton claimed to have met Galileo in 1638, during his tour of Italy, and discussed
