596 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 400:1, the torque downstream is measured in foot x pounds rather than in ounce x inches. This means that if we energize the magnetic clutch with the motor running at, say, 2 x 286.2 pps, 1 or more of the set screws will slip, and it is not prudent to use pins instead of set screws because of the possible failure of a micro-limit-switch at the 0 or 75 ø positions. Thus for the present we are content to use 15 min per scan. Photographs of the instrument are shown in Figs. 14 through 17, inclusive elements of interest are pointed out in the captions. THE SAMPLE HOLDER GP curves of tresses of hair do not provide results as precise as those obtained from monolayers of parallel oriented fibers, and once a decision was made to use that ap- proach, it was necessary to design and fabricate a versatile reliable rack on which a number of fibers sufficient for obtaining a GP curve could be strung, unstrung, and restrung in a reasonable time, e.g., 15 min or less per stringing. A photograph of most of the elements involved can be seen in Fig. 18 the caption provides further explana- tion. Figure 16. Cavity of GP-2 with fiber rack in place

OPTICAL PROPERTIES OF HAIR 597 Figure 17. Same as Fig. 16 but with fiber rack removed. Both rotatable Polaroid discs are in E• position with levers against pin stops. Item in upper portion of picture moves with mechanized (detector) telescope and actuates microlimit switches at 0 ø (moving down scale) and 75 ø (moving up scale) EXPERIMENTAL PROCEDURES The fibers are strung using as a visual aid a "swing-away" monocular (focal lenth --3.5 in.) placed on a spectacle frame the distance from lens to eye should be adjusted so as to provide a working distance of •4 in. In order to be able to use angles of incidence and observation as large as 75 ø from the normal and illuminate or "see" only the fibers, it is necessary to separate the 2 screws on the sample rack by 7 in. and the keyed shafts on which the washers are mounted by 9« in. this means that the fibers have to be • 12 in. long. If hair that long cannot be obtained, it is lengthened by glueing it to a similar hair fiber with cyanoacrylate glue. Fine-bore hypodermic syringe needles are used in pairs to guide the ends of the fibers close together before making the joint. The joints have to be positioned so thay they will not be illuminated or observed. From the traces (•, RER, • equals 30 ø) we record on our data sheets the counts for the area (S + D), the peak voltage value s• for the front-face peak, and the voltage values of diffuse scat- tering d0 o, and d•.•o. In a separate experiment, by means of the zero-adjust potentio- meter of the recorder, the baseline is moved, say, 0.2 V up scale and the integrator pen allowed to provide the number of counts equivalent to the area (0.2 V x 15 min). The area (D) between the baseline and the ordinate values at 0 and 75 ø will be 15/2 x