Proposed International Survey of the Sky

Abstract

ON the initiative of the French National Meteorological Service, it has been decided to take photographs of the clouds three times daily during the week September 17–23, inclusive, at as many stations as possible throughout the countries of western Europe. As the number of official meteorological stations is limited, it has been proposed to enlist the services of those professional and amateur photographers who are willing to co-operate voluntarily in the work. The photographs should be taken as nearly as possible at 7 A.M., 1 P.M., and 6 P.M. G.M.T. (not summer time). The photographer should make a note of the direction in which the camera is pointing when the photograph is taken (e.g. north, south-west, etc.); if more than one photograph is taken at any hour it will be advantageous to take them in opposite directions (e.g. south-west and north-east). A reseau of five photographs would practically cover the whole visible sky when an average lens is employed, and it is accordingly recommended that, when possible, one photograph should be taken towards each of the points north, east, south, and west, and one towards the zenith. Photographers should be particularly careful to mark their plates in some way, so that the photographs in the different directions may be readily recognised after development; the inclusion of a small strip of horizon might be advisable for this purpose. In the case of the zenith photograph, a small part of some object might be included (e.g. the top of a tree or the corner of the roof of a house) to indicate the orientation of the plate.