A Comparative Study of Vibration Absorbers.

Abstract

Vibrations in laboratories always cause great annoyance, a n d frequently either prevent the employment of sensitive instruments altogether or necessitate the installation of elaborate and mechanically unstable suspensions.T h e purpose of this study was t o work out a method €or determining the relative value of different devices and materials in absorbing vibration. A review of the available literature showed t h a t very little had been published on vibration in buildings. Some very careful and valuable work has been done by Prof. E. E. Hall,% of the University of California, in buildings in San Francisco and Berkeley.L 1 FIG. 1-SIMPLE PENDULUM FOR RECORDING HORIZONTAL VIBKATIONS Deutsch3 has done work in New York City, and a few descriptions of instruments for measuring vibration have appeared in t h e engineering magazines. With few exceptions the instruments which have been described for the measurement of vibration are constructed on the principle of the seismograph.s A pendulum of some type constitutes the fixed mass in the measurement of the horizontal component of the vibration a n d a weighted helical spring in t h e measurement of the vertical. T h e apparatus which was used for obtaining records of horizontal vibration is shown in Fig. I . It con-' sisted of a simple pendulum weighing about 2 5 lbs., and having a period of vibration of approximately one second. A very light aluminium recording needle was connected t o this pendulum in such a way as t o give about a 20-fold magnification on t h e record sheet. For vertical vibration we used t h e apparatus shown in Fig. 2, consisting of a helical steel spring, No. 14 wire, about three-fourths inch in diameter and 1 2 in. long when unstretched, and loaded with a lead bob weighing about 3 lbs. T h e bob was constrained t o movement in one vertical plane by knife edges. Vertical motion relative t o the bob was transformed into horizontal by a system of very light aluminium levers

Laboratory simulation of the generation of the spiral structure of galaxies (theory and experiment)

“…books now available, it must suffice here to mention only a few (e.g. Crede 1951, Den Hartog 1956, Macduff and Curreri 1958, Ker Wilson 1959, Rausch 1959, Bishop and Johnson 1960, Harris and Crede 1961.…”

“…General methods of calculating the six natural frequencies of a seismic mounting are well established (e.g. Crede 1951, Ker Wilson 1959. A mounting (Macinante unpublished) designed t o satisfy this requirement comprised a base block fixed on the floor, and a seismic top weighing about 350 lb supported by springs on the base block.…”

Microchemical Balances. Errors of Kuhlmann Balance

“…Experiments with cacotheline in the authors' laboratory failed to give satisfactory quantitative results. Tartakovskil (12) used hematoxylin for the colorimetric determination of tin. The concentration of tin required ranges from 0.3 to 2 mg. per liter of solution.…”