THE intensive international study of meteorology during the Second International Polar Year, 1932–33 includes also the sky, and General Delcambre, president of the International Commission for the Study of Clouds, selected two periods for specially detailed investigation in France and neighbouring countries. The first was on April 12 and 13, while the second is arranged for July 12 and 13, 1933, and General Delcambre has asked for material from England. Should conditions on July 12 and 13 be suitable, meteorologists with cameras are asked to take at least three cloud photographs each day, as near as possible to the hours of 8 a.m., 2 p.m. and 7 p.m. B.S.T., and others at intermediate hours whenever the general character of the sky changes. The purpose of the photographs is to represent the changes of the sky as a whole, and cloud-systems should be photographed rather than individual clouds, using, for preference, a wide-angle lens. Artistic merit is a secondary consideration; the prints should show as much detail as possible, but should not be re-touched. Filters should be used if necessary to bring out the structure. It is important that the following information should be given on the back of each print: name and address of the photographer, place where taken, date and time. It is desirable also that notes should be added as to the fraction of the sky covered by cloud, the nature of the clouds in the part of the sky not included in the photograph, the direction in which the camera was pointing and the approximate elevation above the horizon. Prints, suitably packed, should be addressed to: M. le Ministre de l'Air, Office National Metéorologique, 196 rue de l'Université, Paris 7, and in the corner should be written “Année des Nuages”.