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The instrument described here is essentially a time-encoder, which directly gives a digital read-out of capacitance, inductance or resistance, by measuring the transient response of an RC or RL circuit to a step-voltage input. This simple device can easily achieve high accuracy, which mainly depends upon three resistance standards. Time-encoding permits fast measurement, and impressively wide range, covering several decades, substantially independent of the dissipation factors of capacitance or inductance. It can be used as a laboratory instrument or for batching operations in the mass manufacture of electronic components and sampling reactive transducers on board an instrumented space vehicle. High speed of measurement and availability of digital read-out make it fit ideally into computer interfaces. Problems peculiar to the device in sampling applications are discussed in detail.

Two methods of determining the differential cross-section taking into account the effects produced by a non-uniform and non-parallel beam and finite dimensions and absorption of the target, are described, one requiring complete beam data, and the other using only scattering data. Their relative merits are discussed regarding statistical errors showing that the detector geometry plays a crucial role.

A hybrid computer for structure factor calculations in X-ray crystallography is described. The computer can calculate three-dimensional structure factors of up to 24 atoms in a single run and can generate the scatter functions of well over 100 atoms using Vand et al., or Forsyth and Wells approximations. The computer is essentially a digital computer with analog function generators, thus combining to advantage the economic data storage of digital systems and simple computing circuitry of analog systems. The digital part serially selects the data, computes and feeds the arguments into specially developed high precision digital-analog function generators, the outputs of which being d.c. voltages, are further processed by analog circuits and finally the sequential adder, which employs a novel digital voltmeter circuit, converts them back into digital form and accumulates them in a dekatron counter which displays the final result. The computer is also capable of carrying out 1-, 2-, or 3-dimensional Fourier summation, although in this case, the lack of sufficient storage space for the large number of coefficients involved, is a serious limitation at present.

For radiometric or photometric instruments using collecting optics, the étendue or collecting efficiency varies with distance for near objects, causing significant errors. Variation in effective collecting area as well as in solid angle with distance has to be considered. Errors for a thin lens and a Cassegrainian system are compared. Moving the secondary for focusing greatly reduces this variation. The ratio of primary to secondary focal length also plays an important role. Proper choice of this ratio can minimize the variation in the field of view, improving the depth of focus. Calculations are useful for extending the range of instruments or for calibration by near sources.