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A SIMPLE experiment has been carried out which shows the importance of the rate of loading on the fracture characteristics of a unidirectional composite. Three specimens of flexibilized epoxy resin, 12.7 mm × 6.4 mm in cross-section and 50 mm test length reinforced with 3 volumes per cent continuous silica fibres in unidirectional array, were loaded to fracture at 0.051 mm/min, 5.1 mm/min, 510 mm/min respectively, at room temperature. Fracture was deliberately encouraged by forming a small notch at one side of each specimen and a tensile crack then spread in the resin to the opposite side. Fibre fracture did not coincide with resin fracture but was spread over a region on either side of the resin crack.

IN 1929 we published evidence (Proc. Roy. Soc., B, 104, 561; 1929) showing that in preparations made from ergosterol by exposure to ultra-violet radiation, and subsequent removal of unchanged ergosterol, there was a close correlation between antirachitic activity and intensity of absorption for radiation of wave-length 280 mμ. On this and on other evidence we argued that it was probable that vitamin D was the substance present in these products which was responsible for the intense absorption band with heads at 280 mμ, and 271 m (substance A). We have now obtained definite evidence that this inference is not correct, and that the reactions which occur on irradiation of ergosterol are more complex than then appeared probable.