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In his recollections Newton describes how he made his greatest discovery:

In August 1665, Sir I., who was not then not 24 brought at Sturbridge fair a Prism to try some experiments upon Descartes's book on colors & when he came home he made a hole in his shutter & darkened the room & put his Prism between that & the wall... etc.

My question: who and for what reason was making prisms and selling them in the market? There must have been some demand. Who was buying them them and for what purpose?

Edit. My earlier naive conjecture was that there were some scientific equipment makers catering to Cambridge scientists:-) But this is refuted by two facts: a) First of all this did not happen in Cambridge. Newton was at that time on quarantine in his mother's estate, far from Cambridge. And b) scientists in Cambridge were not interested at that time in scientific experiments: they studied mostly theology and Aristotle's writings.

Westfall in his most comprehensive book about Newton, "Never at rest", writes: "Newton's recollection of Sturbridge Fair may have been mistaken, there was also annual Midsummer Fair which managed to escape both plagues. If he purchased the prism there in 1665, he could have taken it home with him and performed there basic, though perhaps crude, experiments connected with his initial insight".

He also mentions that "prisms seem an unlikely item of commerce for a small market town" but does not elaborate on this.

Alexandre Eremenko
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  • There were deck prisms: https://en.wikipedia.org/wiki/Deck_prism and there was maybe prism lighting https://en.wikipedia.org/wiki/Prism_lighting – Pieter Mar 14 '21 at 00:26
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    @Pieter: interesting! Any evidence of these devices in 17th century? – Alexandre Eremenko Mar 14 '21 at 02:25
  • There is a patent by Wyndus from 1684: https://glassian.org/Prism/Patent/GB1684232/page1.html – Pieter Mar 14 '21 at 22:33
  • @Pieter: what is the evidence that this is about prisms? I did not find the word in the patent. Besides, this only deepens the mystery: the guy "hath with great labour and expense obteined...", while Newton, 19 years earlier was simply able to buy his Prism in a village market:-) – Alexandre Eremenko Mar 14 '21 at 23:01
  • It seems to be the earliest mention of something that may have acted as a deck prism, https://glassian.org/Prism/Gallery/Deck/index.html The "labour and expense" may have been to produce glass that was sufficiently clear at the thicknesses that were required for such applications. – Pieter Mar 14 '21 at 23:13
  • @Pieter: besides the later dates, everything shown in these figures are quite crude items, while Newton probably used a finely polished prism with strictly flat faces in his experiments. Otherwise he would see a complete mess on his screen. – Alexandre Eremenko Mar 14 '21 at 23:22
  • The house which my great grandparents rebuilt and redecorated about 1917 had table lamps with prisms dangling from them. So obviusly prisms were made for use in lamps by 1917. Of curse that is about 250 years before Newton's experiments. – M.A. Golding Mar 15 '21 at 18:37
  • M.A. Golding: yes, lamps and chandeliers decorated with prisms came into fashion in the late 18 century. But these were not the prisms that Newton used: the link in Pieter's answer contains photos of some prisms from Newton's times. – Alexandre Eremenko Mar 16 '21 at 01:15

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Maybe some of Newton's prisms were preserved. An article by A.A. Mills (1981) shows images. He writes:

Newton appears to have purchased all his prisms: there is no intimation that he made any of them, although he was obviously skilled at grinding lenses and mirrors. This availability of ready-made glass prisms is rather puzzling, for the period in question appears to pre-date the earliest recorded chandeliers, which in any case contained facetted droplets rather than triangular prisms. Presumably there was sufficient demand for prisms to be made and sold purely as curiosities or toys, the optical quality being correspondingly low.

But also:

None of the extant prisms claiming an association with Newton can be identified with any of his recorded prisms.

Pieter
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  • Newton's optics experiments lasted several years. Later he could have made them on special order with instrument manufacturers. But the first one, according to his recollections was simply purchased in a market. – Alexandre Eremenko Mar 14 '21 at 23:46
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    The article you linked indeed seems to address the question in depth, and carefully summarizes what is known on the subject. – Alexandre Eremenko Mar 15 '21 at 11:21