Two preliminary determinations of the Newtonian constant of gravitation have been performed at Los Alamos National Laboratory employing low-Q torsion pendulums and using the time-of-swing method.Recently, Kuroda has predicted that such determinations have an upward bias inversely proportional to the oscillation Q, and our results support this conjecture. If this conjecture is correct, our best value for the constant is ͑6.6740 6 0.0007͒ 3 10 211 m 3 kg 21 s 22 .Interest in the value of the Newtonian gravitational constant, G, has increased recently with the publication of several disparate results [1][2][3][4]. This discrepancy, as much as 50 standard deviations, is an error unheard of in the measurement of any other of the fundamental constants. A torsion pendulum instrument has been assembled at Los Alamos National Laboratory which determines G by the method of Heyl, also called the time-of-swing method, and preliminary results of this effort are reported herein. Kuroda has shown [5] that popular models of anelasticity predict a bias in these determinations where the damping of the pendulum is caused by losses in the suspension fiber, and this upward fractional bias should be 1͞pQ. Two determinations were carried out employing systems which differ in Q by a factor of 2, and the disagreement of their results is consistent with that predicted by Kuroda.In a time-of-swing, or Heyl-type, measurement, the oscillation frequency of a torsion pendulum is perturbed by the presence of source masses. In their absence, the free oscillation frequency, squared, is related to the moment of inertia, I, and fiber torsion constantThe interaction potential energy of the pendulum and source masses, U g ͑w͒, contributes a "gravitational torsion constant,"where w is the angle between the axis of the pendulum and that of the source masses. Therefore, the frequency of small oscillations of the pendulum isThe gravitational torsion constant is at a maximum when the pendulum is in line with the source masses (w 0, or "near" position), and at a minimum when it is perpendicular (w p͞2, or "far" position). It is proportional to G, and is calculable from the geometry and densities of the pendulum and masses, so the gravitational constant is given bywhere k g K g ͞G, and D͑v 2 ͒ is the difference of the square of the frequencies recorded at the two orientations.The above derivation assumes that k g remains the same at each orientation, but this assumption has been called into question recently. Interest in gravitational wave detectors has spurred research into the anelastic properties of suspension materials at low frequencies, and one model of anelasticity has been shown [6-8] to predict accurately the behavior of several different materials. This model treats a physical spring as a perfectly elastic spring in parallel with a continuous number of Maxwell units, characterized by a spectrum of relaxation times. The model predicts that the torsion constant is a function of oscillation frequency. Kuroda [5] has shown that, for a Heyl-type measu...

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A short duration (1 or 2×10−8 second) high-intensity explosive light source, that may be used in the laboratory, has been proved experimentally. The charge, weighing 4.8 grams, yields a luminosity estimated in the neighborhood of 8×107 lumens. Pictures of high-speed shocks in air, transparent solids, and metal jets have been taken using this lighting system.