Sir Isaac Newton's Prisms

Abstract

IT is reported from Italy that three optical prisms formerly belonging to Sir Isaac Newton have now found a permanent resting place in the Museum of Treviso. The prisms in question were originally in the possession of Newton's step-niece, Mrs. Conduitt (1680-1739), who spent some fifteen years looking after Newton's house, until her marriage in 1717, to Mr. Conduitt, Newton's successor at the Mint. They were acquired from Mrs. Conduitt by Count Francesco Algarotti, a Venetian nobleman and a prominent figure in London society during the middle eighteenth century. After many changes of ownership the prisms were deposited some years ago in the Treviso Museum, to which institution they were recently bequeathed by the late Prof. Luigi Bailo. Although there seems little doubt that these prisms were at some time associated with Newton, it is not easy to assess what part they played in the fundamental discoveries and subsequent work of Newton on the dispersion of white light. Signor Algarotti was a great admirer of Newton and was the author of “Sir Isaac Newton's Philosophy explained for the Use of Ladies”. In the English translation, published in 1739, we learn (vol. 2, p. 70) that Algarotti had found that the prisms available in Italy were unsuitable for repeating Newton's experiments, but that he had been fortunate enough to receive from England some which proved excellent. Later in the same volume (p. 129) we read “I have myself seen the first telescope [Newton's reflecting telescope] … preserved in a city of England … with this are treasured up those prisms which the first time differently refracted the rays of light in the hands of our great philosopher…” There is no doubt that from about 1664 onwards Newton used many prisms in his experiments and fortunately one of these, at least, is preserved in Great Britain; it was presented in 1927 to the British Museum by the Rev. H. T. Inman, who in a private publication has very carefully traced its descent from Newton. It is made of flint glass, and confirmatory evidence of its date has been adduced from the nature of the glass.