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238 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Manipulation of the hair in the apparatus was effected by a polythene sleeve and glove, sealed to the Perspex sheet (Fig. 1). The apparatus is considered under the headings: Charge generation charge detection charge measurement charge removal humidity control. Charge generation A lock of hair of standard weight and length, tied at the root end, was drawn upwards through a fixed number of teeth (six) in an ordinary poly- styrene comb which was clamped horizontally in a Teflon collar to avoid undue leakage to earth. The end of the clamp holding the comb passed through the Perspex wall of the humidity chamber to a rack and pinion device, which moved the comb in a horizontal direction to and from a freely suspended gold leaf. Further insulation against leakage was provided by a second Teflon collar between the clamp, and the rack and pinion. Care was taken to distribute the hair evenly between the teeth of the comb and to commence the passage of the hair one inch below the knot, thus giving an effective length of 15 cm. A standard rate of pull was used, taking about one second for each stroke. The number of strokes used to generate the charge was standardized at five, though some of the earlier tests were performed using ten. After generating the charge, the hair locks were suspended from a rack in the chamber so that a constant humidity could be maintained throughout the experiment. The comb was washed in soap and water and then thoroughly rinsed at regular intervals, preferably after each series of experiments. Charge detection Several principles were examined, but the most efficient and the one adopted made use of the attraction of a strip of gold leaf by the charged comb. The leaf measured 1 X 4 X 0.00004 cm and was held close to, but not touching, a backing sheet of aluminium foil of the same area. The whole was supported by an insulated structure of Teflon and glass, so that the bottom edge of the leaf was exactly opposite the ends of the teeth of _the comb. As far as possible the gold leaf was not disturbed, although since the method was used for making comparisons between treatments, a control treatment was always included in any given series of tests. The following points should, however, be noted: (i) Since the point at which the leaf just moves was used as a measure of the charge, no undue load was ever placed on the leaf. It could therefore be used for an indefinite period without being replaced.