Letter: DNA discovered by deduction

YOUR SCIENCE correspondents are misleading when they write that the elucidation of the double helix model of DNA structure 'was a matter of inspired guesswork rather than logical deduction' ('Hunters of the double helix - 40 years on', 25 April).

The point about this discovery is that it was the product of logical deduction in that Watson and Crick, by making models, applied theories about the structure of the molecule to explain a set of observations. This was in contrast to Franklin's inductive approach, which was to draw generalisations from her observations.

The hypothetico-deductive approach of Watson and Crick led them to the solution of the problem rapidly, contradicting a commonly held misconception that scientists work in small incremental inductive steps.

James Cambridge

Bristol, Avon