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(1986). Berkeley's semantic revolution: 19 November 1707–11 January 1708. History of European Ideas: Vol. 7, No. 6, pp. 603-607.

A rotating gravity gradiometer measures the mass of an object by detecting its gravitational force gradient. If properly balanced, the device can demonstrate a high level of accuracy and sensitivity. Various unbalances in the gradiometer system give rise to internal mechanical noise. This paper identifies the major sources of unbalance and establishes the degree of manufacturing exactness required to control noise generation. The dynamic gradiometer is a rotating device and is subject to shaft translations caused by misalignment of the rotor and the rotating center of mass. An elliptical shaft translation will be induced by anisoelasticity in the gradiometer bearings. Such motion generates anomalous excitations by coupling through any further unbalance internal to the gravity sensitive mechanism. We have found that the internal mechanical noise is directly proportional to the product of these three unbalances. In addition, for operation above shaft resonance the noise coupling is independent of rotational speed. Below resonance, noise is proportional to the fourth power of speed. Near-future gradiometer application requires a gravitational gradient sensitivity level of 0.5 Ebtvos units (EU) (^10 ~n g/ft). Using presently available suspension, drive, and electronic systems, all three balancing requirements will lie between 0.1 and 0.01%. ROTATING gravity gradiometer can perform sensitive measurement of the earth's vertical gradient. These sensors can also be used on spinning lunar orbiters to measure the mass distribution of the moon, and on spinning deep space probes to measure the mass of the asteroids. A rotating gradiometer can measure the mass of an object at a distance by using a rotating system of masses and springs to detect the gravitational force gradient field of the object.1 The dynamic (or rotating) gradiometer, in its simplest form, consists of one or more low-level accelerometers mounted to a rotating frame with the sensitive axes perpendicular to the centrifugal force.2 When this is done, the output of the accelerometers will be found to contain dynamic components at multiples of the rotation frequency which are driven by the various gradients of the field. In particular, the components of the nth-order gradient, when examined in the rotating reference frame of a sensor, will be found to have time-varying coefficients, which are at n times the rotational frequency of the sensor.8 For example, if a simple spring-mass is rotated in a static gravitational field, the gravitational force gradient of the field (second rank gravitational tensor) will induce dynamic forces in the sensor with a frequency which is twice the rotation frequency of the sensor.4 The basic idea behind the operation of these sensors is an old one in electronics—the concept of chopping. This is used extensively in d.c. amplifiers, where the low-level d.c. signal is chopped, transformed into an a.c. signal, and then amplified and measured by phase sensitive detectors. In the gravitational sensors, the chopping of the static gravitational field is accomplished by physically rotating the sensor so that its

Cesium vapor ionization on porous tungsten substrate creates gradients in surface atom concentrations diminishing ionization efficiency

A hybrid computer study has been made of the temperature fluctuations of a satellite as it orbits the earth, passing periodically from sun to shade. The satellite is a thin-walled cylindrical shell, and the plane of the orbit is parallel to the sun's rays. The sources of heat input are direct sunlight, thermal radiation from the earth, and internal heat generation. The direct solar input is of a sinusoidal variation with diminishing amplitude in both space and time; the earth radiation is constant. The resulting temperature equation is parabolic, with a time-vary ing source term and a nonlinear sink term. The steady-state solution is a limit cycle, where the temperature at all points on the satellite surface continually oscillates between some maximum and minimum, as the satellite passes in and out of the sunlight. A hybrid computer was programed and solutions to the temperature equations obtained. The complete temperature distribution, as it fluctuates with orbital position, was mapped by the computer. In the hybrid technique, heat conduction between various satellite elements was simulated by a resistor network, while the digital computer generated the timevarying heat loads and simulated the thermal time lags.

Rate of formation of tungsten oxide in porous sample, noting increase in rate of oxidation due to porosity effect

Vibrational mode behavior of rotating gravitational mass sensors and sensor design to minimize nonideal effect of manufacturing and external disturbances

Feasibility design study of solar powered ion propulsion system for interplanetary spacecraft

The aim of this paper is to describe and comment on Bishop Berkeley's connection with An essay on spirit (1750) and its author. This connection, I try to show, is of interest for, among other reasons, the light it throws on the early influence of Berkeley's Siris: a chain of philosophical reflexions . . . (1744); but though the connection has been noticed, it has not been examined in any detail. I have divided the paper into two sections and an appendix. Section I deals with the question of the authorship of An essay on spirit-which I shall refer to as the "essay"-and Berkeley's connection with the author.' In section II, I examine Berkeley's place in the essay and, in that context, the essay's theory of spirits and its relationship to Berkeley's own theory of spirits, as it is presented in Siris. In the appendix, I present a short letter by Berkeley about the essay, which has escaped the notice of his editors.