14 DECEMBER 1951, Page 20

Guide for Travellers SIR, — General Hilton has, apparently, found it difficult

to escape the attentions of secret police in Eastern Europe. I have found the following technique adequate in several countries. Mount a tram, noting that no one mounts with you. Get off where no following vehicle is in sight. Repeat the process several times. Unless the secret police have cloaks of darkness, the method is effective.—Yours faithfully, J. B.S. HALDANE.

University College. London, Department of Biometry, Gower Street. W.C.1.