Letter from Dugald Clerk to W H Errington, 20 Cranmer Avenue, West Ealing, London Explaination of why a heat-ray weapon suggested by Errington would not work. Errington's idea, to focus the rays of an electric arc lamp of 3,000 degrees centigrade using a polished brass reflector, is 'based on a fallacy'. Clerk concludes that no useful result could come of it. 3 July 1915