The thickness of the film formed by each of five lubricants between a pair of disks in rolling contact has been measured by an X-ray technique for a range of loads (80,000 to 225,000 psi maximum Hertz stress), two temperatures (178 F and 250 F), and three speeds (4300 fpm to 9100 fpm). An empirical formula fitted to the X-ray data shows a much higher sensitivity of film thickness to load than is normally predicted. In order to judge whether the measurements themselves are at fault, the X-ray measuring process has been reexamined for accuracy, especially where load-dependent errors might arise. Some weaknesses are noted, such as in the amount of X-ray absorption, but these should not affect load sensitivity greatly. New experiments designed to find effects of imperfect collimation of X-rays indicate that reflection of X-rays may be significant, but these effects too do not seem to account for the anomalies of the film thickness measurements.

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