Sir: Paul Johnson writing on 'Epistolary dons' (19 November) evidently lives a very sheltered life insulated from the harsh realities of the academic world if he really thinks that in writing from my university address I 'lined up the entire University of Reading' behind my earlier comment on the oil industry's veracity. His more worldly friends would have told him how prepos- terous it is to think that one could line up university dons en masse behind anything.
More seriously, my letter to which he alludes was concerned with the technology of processing the organic molecules in petroleum to produce high-octane petrol, a subject among those on which I lecture at this University as Professor of Organic Chemistry. On such an esoteric topic, it is important that I should be seen to write from a position of professional authority: I am, as it were, placing my scientific reputation as security for the accuracy of what I write. That is why I wrote from this address, and why I do so now.
On the other hand, it is not unknown for paid employees of the oil industry to write letters for publication from a private address to support the industry's policy, but without revealing their financial interest. Yet Paul Johnson says nothing on this practice.
One way of distinguishing the profes- sional from the dilettante is to see who takes the trouble to get the facts right. It is therefore relevant that my letter in question was published in the Sunday Times (6 November), not the Guardian as stated by Mr Johnson.
Professor of Organic Chemistry, Department of Chemistry, University of Reading, Whiteknights, Reading