William Herschel

From September 1773, while working as a music teacher and concert director in Bath, Herschel began making his own reflecting telescopes. His memoranda, as edited by Dreyer, record that he hired a two-foot reflector, bought a Bath amateur's mirror-making tools on 22 September, and worked from Smith's Optics and Emerson's Mechanics; Dreyer counts 2,160 recorded operations on mirrors in the four folio volumes of his record, which runs to December 1818.

On 28 October 1783 Herschel began 'sweeping' the sky with a new 20-foot reflector at Datchet. After 41 sweeps made alone, Dreyer says, he judged the method too tiring and of little value; a workman then raised and lowered the telescope while his sister Caroline wrote down the observations, and from Sweep 46 on 18 December 1783 the series continued to Sweep 1112 on 30 September 1802.

In a paper read to the Royal Society on 27 March 1800, Herschel wrote that trials of coloured darkening glasses for viewing the sun had made him doubt that every colour of sunlight heats equally. He set thermometers beside a prism's spectrum, moving one into a chosen colour while two stayed in the shade as standards, and repeated the runs.

On 13 March 1781, during a systematic review of the sky at Bath, Herschel noted in his journal 'a curious either nebulous star or perhaps a comet'; on 17 March he recorded that it had changed its place. His paper to the Royal Society was titled 'An Account of a Comet', and Dreyer reports that the version first presented contained a paragraph arguing for a measurable parallax, which was not printed after more accurate observations elsewhere disproved it.

The difference between the presented and printed versions is consistent with a willingness to drop an argument that later measurements did not support. It is one episode, and other passages in the record show him restating positions when criticised. Belief Updating

In December 1781 William Watson wrote to Herschel that people in London doubted the high magnifying powers he had used, and that Maskelyne and Aubert said they had never seen fixed stars round and well defined. On 7 January 1782 Herschel replied that 'seeing is in some respect an art which must be learnt' and that he had 'many a night' practised it, and he later urged Aubert to raise his powers by degrees; in his own memorandum, his telescope was then tried at Greenwich in May and June 1782 and judged by those who used it to exceed other instruments.

His letters treat good observing as a skill built by repeated practice, which is consistent with a mastery orientation. The evidence is largely his own words and his own memorandum, so it is illustrative rather than conclusive. Mastery Orientation

Dreyer places the turning point of Herschel's life in the winter of 1772-73, when reading Smith's Optics made him want to see the heavens for himself. His memoranda show a quadrant bought on 19 April 1773, an object glass on 24 May, and mirror-making tools on 22 September, while he still attended 46 private pupils in the week of 15 November 1773.

Building instruments from books and a Bath amateur's cast-off tools while carrying a full teaching load is consistent with resourcefulness. The account rests on his own memoranda and his sister's later recollection. Resourcefulness