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1 Intravenous propranolol and practolol both reduced resting supine heart rate in patients with hyperthyroidism. Propranolol produced a significantly greater reduction than practolol, which did not have a dose-dependent effect. 2 The effect of these drugs on resting heart rate was much less than their effect on the tachycardias produced both by severe exercise and by standing upright in hyperthyroid patients. Propranolol again produced a significantly greater reduction than practolol in each situation, but practolol did have a dose dependent effect on exercise heart rate. 3 The percentage reduction of standing tachycardia produced by the two drugs appeared to parallel closely the reduction in exercise tachycardia. 4 It is concluded that a simple and convenient way of assessing the activity of β-adrenoceptor blocking drugs in hyperthyroid patients would be to measure their effect on the tachycardia induced by standing. Their effect on resting heart rate should not be used. 5 Practolol may be useful in the management of hyperthyroidism in patients in whom propranolol and similar non-selective β-adrenoceptor blocking drugs are contraindicated.

Studies using both n-hexane and transformer oil stressed with direct voltage have indicated that, for nonuniform electric fields, cavitation may be produced together with associated gas-initiated light emission and acoustical disturbances. Transformer oil is shown to emit light below the cavitation-onset stress by an assumed electronic electroluminescence which is also invoked to explain light emission under uniform field conditions. Cavitation onset is shown to be strongly temperature dependent. Tests at elevated temperatures indicate that the discontinuities which were found in the conduction characteristics are not associated with bubble formation or collapse, and alternative explanations are offered. A distinction is drawn between the integrated conduction characteristics and the current pulse behaviour which accompanies the gas-phase disturbance in the liquid.

Carefully controlled measurements of the electric strength of transformer oil are reported. Electrodes of large-diameter cylindrical geometry are used to obtain substantially uniform fields with an electrode area of up to 2m2. The results indicate the important influence of oil volume on the electric strength both for supply-frequency and 1/50?s-impulse voltages. The effects of temperature, forced oil motion and the nature of gas in solution are also studied, and it is concluded that the oil flow is an important parameter in determining the statistical distribution of breakdown measurements. The test results have been explained on the basis of gas-initiated breakdown.

The breakdown of a dielectric liquid in a practical environment is described by a hybrid statistical distribution based on the `weak-link? principle. By forming a convolution of two random processes with distinct distributions, it has been possible to relate certain parameters, of a breakdown test to the statistical behaviour of the dielectric. The application of this concept to the prediction of electric strength for large volumes of liquid is indicated.