Measurement of the biologically active ultra-violet rays of sunlight

The ultra-violet radiation was measured by the acetone methylene-blue method described by Webster, Hill and Eidinow. Readings were taken at the Meteorological Office, Kingsway, The Royal Observatory, Greenwich, the States Meteorological Station, Guernsey, the National Institute for Medical Research, Hampstead, and by voluntary observers elsewhere, viz., by Dr. Adams, Liverpool Sanatorium, Frodsham, Cheshire; Dr. Paul Tozer, Peppard Common Sanatorium, Oxon; Dr. Segaller, St. Ives, Cornwall; A. R. Tankard, Esq., Hull; Dr. Wyatt, Wingrave, Lyme Regis; H. J. Sargent, Esq., Bexhill; C. L. Rivers, Esq., Harrogate; Dr. Dorno, Davos, Switzerland; J. Fyfe, Esq., Stirling; S. M. Bower, Esq., Huddersfield; R. Robertson, Esq., Lowes­toft; F. R. Gray, Esq., Yentnor; R. L. Massey, Esq., Khartoum; Dr. P. W. Moore, Assouan; Dr. Rosenheim (some records in Egypt). The standard acetone methylene-blue is made up from a 0.1 per cent, solution of Paulene Freres methylene-blue; 5.8 c. cm. of this is added to 30 c. cm. of pure distilled acetone, and made up to 100 c. cm. with water; this gives a standard labelled 10. The standard solution is kept in brown glass bottles. A standard silica tube, as shown in fig. 1, 3 mm. in diameter, is filled with this solution and exposed to the sunlight. At the end of the exposure the colour is compared with the colour of eight standard tubes (fixed and unbleachable). These standard tubes are marked 3, 4, 5, 6, 7, 8, 9 and 10, and are placed in a suitable frame for comparison. The standard solution used for bleaching in the silica tube is matched against these standard tubes, not only after the period of exposure, but also before exposure, since the standard solution (10) may very gradually fade, while also the refractive power of the silica tubes may vary.