The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science. Richard Holmes
wrote to London for materials to construct a five-foot reflector, but was told that no one made glass mirrors large enough (at least five inches in diameter) to fit it. It was then that Herschel took the crucial decision to try to cast, grind and polish his own metal mirrors or specula. To start with, he acquired some metal grinding and polishing tools from John Michel, a Quaker astronomer who had retired to Bath nursing some strange, unacceptable ideas-such as the existence of ‘black holes’ in space from which light itself could not escape.
The accelerating pace of Herschel’s experiments is caught in a memorandum of his purchases made over five months in 1773.
May 10th. Bought a book of Astronomy, and one of Astronomical tables.
May 24th. Bought an object glass of 10 foot focal length.
June 1st. Bought many eyeglasses, and tin tubes; made a pair of steps.
June 7th. Glasses paid for, and the use of a small reflector paid for.
June 14th. The hire of a 2 foot reflecting telescope for 3 months paid for.
Sept. 15th. Hired a 2 foot reflector.
Sept. 22nd. Bought tools for making a reflector. Had a metal [mirror] cast.
Oct. 2nd. Bought a 20 foot object glass, and 9 eyeglasses. Emerson’s Optics. Attended private [music] scholars as usual.78
In June 1773 Herschel decided to attempt to make his own large reflector telescope, using metal mirrors as big as six inches in diameter.79 It was a complicated and above all laborious task, requiring the casting, grinding and polishing of ‘speculum metal’, made of an alloy of white tin and brass. Three-inch mirrors were quite common, but a six-inch-diameter mirror with a precise concave surface required a technical feat that had never been achieved before. It called for a series of ingenious ‘contrivances’, which took Herschel back to his boyhood days, and all his old enthusiasm and ingenuity bubbled back.
The casting first required the construction of a small iron furnace and special moulds. These, Herschel found after many experiments, could best be made from a dried non-porous natural loam, formed from pounded horse-dung.♣ Once cast, the speculum metal had to be hand-ground with a solution of ‘coarse emory and water’ to achieve the required concave curve, and finally polished, ‘with putty or oxide of tin or pitch’, for hours on end to achieve an absolutely smooth reflective surface. It was an exhausting, and occasionally dangerous, physical process, needing endless trial and error. The furnace was liable to explode, and Herschel found that the polishing had to be done without pausing-sometimes for many hours on end.80 If the polishing paused for even a few seconds in the final stages, the metal would harden and mist over, and the mirror would be useless.
All the work had to be carried out at 7 New King Street, turning the elegantly furnished house (intended of course for music-making and teaching) into a pungent, chaotic workshop. Initially Caroline was appalled at this transformation: ‘To my sorrow I saw almost every room turned into a workshop. A Cabinet-maker making a Tube and stands of all descriptions in a handsome furnished drawing room! Alex putting up a huge turning machine…in a bedroom for turning patterns, grinding glasses & turning eye-pieces etc. At the same time Music durst not lay entirely dormant during the summer, and my Brother had frequent rehearsals at home.’81
Caroline was gradually becoming William’s closest assistant. She was up at all hours, turning her hand to every practical need, housekeeping, shopping in the market, dealing with visiting music scholars, taking Pump Room choirs for singing practice, ‘lending a hand’ in the workshop, even reading aloud from inspiring fiction (in her bad accent) while William sweated over the mirror-polishing.82 Their choice of books seems intended to relieve the monotony of the work: Don Quixote, the Arabian Nights, Sterne’s Tristram Shandy-all tales of fantastic adventures or eccentric heroes. Caroline does not seem to have been permitted the most fantastic and eccentric of them all, William’s favourite, Paradise Lost.♣
Sometimes she even provisioned William while he worked, literally putting drinks and bits of food into his mouth. On at least one momentous occasion, this extraordinary provisioning process lasted for sixteen hours without a break. It was as if Caroline was a mother bird feeding a demented nestling. Something of William’s obsessional dedication, and Caroline’s ambivalent feelings about it, come out in the way she described this in her journal: ‘My time was so much taken up with copying Music and practising, besides attendance on my Brother when polishing, that by way of keeping him alife I was even obliged to feed him by putting the Vitals by bits into his mouth-this was once the case when at the finishing of a 7 foot mirror he had not left his hands from it for 16 hours together…And generally I was obliged to read to him when at some work which required no thinking, and sometimes lending a hand, I became in time as useful a member of the workshop as a boy might be to his master in the first year of his apprenticeship.’83
Much later, Victorian illustrators would make this into a comfortable domestic scene, a harmonious couple in an elegant drawing room, with convenient refreshments on a nearby table. In fact these epic polishing sessions took place downstairs, at the workbench of the unheated, stone-flagged basement in New King Street. Here William and Caroline were surrounded by tools and chemicals, and the distinct, pungent smell of the horse-dung moulds. It was dirty, monotonous and exhausting work, for which they wore rough clothes, and ignored ordinary household routines and niceties.84
Caroline’s account is light-hearted and self-denigrating, in her usual manner, and yet faintly resentful. Her sense of herself as William’s ‘boy’ apprentice suggests a measure of physical subordination and discipline. It also hints at an undignified negation of her sex. Here William was her ‘master’, not her kindly brother or patient teacher. Moreover, she saw herself as his ‘first year’ boy, at a time when apprenticeships normally lasted seven years. Though willingly undertaken, the work must have been frustrating and even perhaps humiliating for her. (What, for example, did she do if William needed to urinate during his epic polishing sessions?) Once again her account of the brother-sister relationship is problematic.
Meanwhile Herschel revealed extraordinary mechanical ability, combining the manual dexterity of a musician with almost ruthless determination and stamina. On one occasion he insisted on sharpening his instruments on the landlord’s grindstone in the yard after midnight, and came back fainting, with one of his fingernails ripped off. On another, the casting exploded in the basement workshop, and a stream of white-hot metal shot across the stone floor, cracking it from end to end and nearly laming them both.
By 1774 Herschel had successfully assembled his first five-foot reflector telescope, with a home-made metal speculum mirror of six-inch diameter (about the size of a side-plate). His Observation Journal records proudly: ‘December. At night I made astronomical Observations with telescope of my own construction.’85 As if to distinguish it from the standard tubular refractors, he had a beautiful octagonal case of gleaming mahogany panels made for it by their cabinet-maker. With its bright brass eyepiece and small sighting scope, it looked like a fine piece of Georgian furniture, not unworthy of Chippendale himself.
It was immediately apparent that Herschel had created an instrument of unparalleled light-gathering power and clarity. He saw, for example, what very few astronomers even suspected: that the Pole Star-which had been the key to navigation, and the poet’s traditional emblem of steadiness and singularity, for centuries-was not in fact one star at all, but two stars. This observation was not officially