The condenser was thoroughly packed all round in cotton-wool to a thickness of 6 inches, and its temperature was indicated more or less by a thermometer plunged through a hole in the lid of the containing box and of the condenser box, and resting on the upper surface of one set of tin-foil electrodes, from which the soft paraffin mixture had been purposely scraped away. The following were the results of a four hours' run at a voltage 50 per cent higher than that for which the condenser was designed--i.e. 3000 volts. Times. Voltage Temperature Temperature Difference in Condenser. in Air. Hrs. Min. 2 10 2750 22.8 deg. C. 23.0 deg. C. + 0.2 deg. 3 10 2700 23.0 deg. C. 23.3 deg. C. + 0.3 deg. 3 18 3200 23.1 deg. C. 23.0 deg. C. -0.1 deg. 4 10 3200 23.3 deg. C. 23.7 deg. C. + 0.4 deg. 5 10 3100 23.6 deg. C. 23.4 deg. C. -0.2 deg. 6 10 3000 23.8 deg. C. 23.35 deg. C. -0.45 deg. An idea of the order of the amount of waste may be formed from the following additional experiment. A condenser similar to the one described was filled with oil of a low insulating power. It was tested calorimetrically, and also by the three voltmeter method, which, however, proved to be too insensitive. The temperature rise in the non-conducting box in air was about 0.3 deg. C. per hour, and the loss of power was found to be less than 0.1 per cent. In the present case the actual rise was only 1 deg. in four hours, and the integral give and take between the condenser and the air is practically nothing; consequently we may consider with safety that the rate of rise is certainly less than 1 degree per three hours. The voltage and frequency were about the same in both experiments, consequently the energy passed is about proportional to the capacity used in the two experiments. From this it follows that since the specific heat of both condensers was the same (nearly), the loss in the present case is a good deal less than one-tenth per cent. The residual charge is also much less than when the condenser is simply built up of paper paraffined in an unsystematic manner, and from which the air and water have been imperfectly extracted, as by baking the condenser first, and then immersing it in paraffin or oil. It is usual to consider that the phenomena of residual charge and heating in condensers, to which alternating voltages are applied, are closely allied. This is true, but the alliance is not one between cause and effect--at all events, with regard to the greater part of the heating. The imperfect exclusion of air and moisture, particularly the latter, certainly increases the residual charge by allowing surface creeping to occur; but it also acts directly in producing heating, both by lowering the insulation of the condenser and by allowing of air discharges between the condenser plates.