Part II: Design and Operation of a Vacuum Vibroscope

Abstract

Measurements at 70° F and various dry-air pressures have been made to estimate the effects of air-damping on vibroscopic determinations of mass per unit length, of bending modulus, and of torsional modulus for European goose feather barbs and down filaments. With the Vacuum Vibroscope which was designed and constructed to facilitate these measurements, it is possible to carry them out in a vacuum or in controlled atmospheres ; e.g., constant relative humidity. In the apparatus, whose operation is briefly described in this paper, a small compact vibroscope which could be enclosed in a glass bell jar was mounted on a metal plate, and appropriate electrical and vacuum connections were made through the plate. For mass-per-unit-length or bending-modutus measurements, the samples were excited into vibration mechanically. For torsional-modulus measurements, a magnetizable crossbar such as a nickel wire was cemented to the sample. and oscilla tions were induced by an alternating electromagnetic field. Significant but relatively small air-damping effects were observed in the determinations of mass per unit length and of bending modulus; the effects observable in the determinations of torsional modulus were much smaller.