9 SEPTEMBER 1972, Page 27

The supernatural

Sir: In James Blish's interesting article (August 19) on the decline of the supernatural there is a point which I think ought to be clarified, particularly in view of his being busy on a work of historical nature.

When Roger Bacon's "four major sources of error" are mentioned it sounds to me as if it might actually be Francis Bacon's four celebrated ' Idola ' that are meant: Idola Tribus, Idola Specus, Idola Fori, and Idola Theatri. (It is true that Bertrand Russell ascribes a fifth to him: 'idols of the schools,' which could be called 'Idola Academiae,' but other writers consider that Bacon overlooked this source of error.) If this is so the reference to 'the midthirteenth century' should be to the begining of the seventeenth, which alters the perspective considerably.

Induction as opposed to deduction is also mentioned in the article. Though not the inventor of induction Francis Bacon attached immense importance to it and in this way contributed to the growth of 'modern science.'

Frank Alan Thompson 13 Eriksbergsgatan, Stockholm, Sweden