Abstract: Method and apparatus to measure the quantity of sebum secreted by the skin, by passing light through the specimen. The light passed through the specimen is modulated at a predetermined frequency, and only light of the same modulated frequency is measured by a receiver. The apparatus includes automatic zero calibration, and several embodiments of stabilized phototransistor circuits.

Abstract: Method and apparatus to measure the quantity of sebum secreted by the skin, by passing light through the specimen. The light passed through the specimen is modulated at a predetermined frequency, and only light of the same modulated frequency is measured by a receiver. The apparatus includes automatic zero calibration, and several embodiments of stabilized phototransistor circuits.

Abstract: Young's modulus and/or the internal damping factor of an elastic material is obtained by subjecting an area of the material to a sustained vibration. The presence of the material being tested changes the resonance of a mechanical resonator and determination of the changed resonance peak enables the required elastic characteristics to be obtained. The sample may be subjected to varying tension during testing and can conveniently be vibrated by signals obtained from a variable frequency generator although, preferably, an electronic circuit for vibrating the resonator has a feed-back loop to operate as an electro-mechanical auto-oscillator.

Abstract: An apparatus for measuring mechanical characteristics of a material capable of transmitting vibration, particularly skin of a living subject. An impulse from a generator such as a small hammer causes a disturbance to propagate a wave along the material. A receiver includes a source of radiation and two photocells spaced apart and isolated from each other. The photocells receive the radiation after reflection from spaced locations on the surface of the material. The travel time of the propagated wave between the two reflection points is measured to determine the speed of wave propagation in the material.

Abstract: An apparatus for measuring the consistency or hardness of a material, for example skin tissue on a living body, comprises a support to be applied against the material to be tested and a feeler movably carried by the support for displacement through a distance which will be proportional to the hardness or consistency being measured. To avoid the need for careful positioning of the device on the test material with a carefully constant bearing pressure, a control circuit is provided for recording the displacement of the feeler only when the bearing pressure of the support on the test material has a predetermined value. The reading of the displacement is held and is preferably digital. Application of the support successively to different points on the test material will enable a true comparison of the readings at the various points.