Another take on achromatic history

Without wishing to spoil Dollond & Aitchison's birthday party, we feel that for the second time we must correct an error in their history book (optician, June 1983). In the article by David Challinor (optician June 9) he states that John Dollond and his son invented the achromatic lens. It was in fact Chester Moor Hall who realised that a convex crown lens combined with a concave flint lens would form an achromatic doublet and, in order to preserve his invention, he used two separate instrument makers - E Scarlett and James Mann - to make the relevant components. However, both these men subcontracted their work to the same optician, one George Bass. Much later, according to Ramsden, Bass passed the details of Hall's work to John Dollond when he became aware of Dollond's interest in the subject. Hall did use his invention to construct an achromatic telescope, one of which was recorded as being in the possession of James Ayscough in 1754 (Gentleman's Magazine, 1790). When the matter was fought over in the court, the trial judge, Lord Camden, acknowledged the priority of Hall for the invention but ruled that : 'It was not the person who locked his invention in his scritoire that ought to profit by a patent for such an invention, but he who brought it forth for the public'. John Dollond must at the very least be thanked for that. RH Sessions Snr & Jnr Felixstowe, Suffolk