Mr. Blakesley described a simple method of determining the loss of power in a condenser by the use of three electrodynamometers, one of which has its coils separate.  Of these coils, one is put in the condenser circuit, and the other in series with a non-inductive resistance r, shutting the condenser.  If a_{2} be the reading of a dynamometer in the shunt circuit, and a_{3} that of the divided dynamometer, the power lost is given by r (Ca_{3} — Ba_{2}) where B and C are the constants of the instruments on which a_{2} and a_{3} are the respective readings.  Prof.  S.P.  Thompson asked if Mr. Swinburne had found any dielectric which had no absorption.  So far as he was aware, pure quartz crystal was the only substance.  Prof.  Forbes said Dr. Hopkinson had found a glass which showed none.  Sir William Thomson, referring to the same subject, said that many years ago he made some tests on glass bottles, which showed no appreciable absorption.  Sulphuric acid was used for the coatings, and he found them to be completely discharged by an instantaneous contact of two balls.  The duration of contact would, according to some remarkable mathematical work done by Hertz in 1882, be about 0.0004 second, and even this short time sufficed to discharge them completely.

On the other hand, Leyden jars with tinfoil coatings showed considerable absorption, and this he thought due to want of close contact between the foil and the glass.  To test this he suggested that mercury coatings be tried.  Mr. Kapp considered the loss of power in condensers due to two causes:  first, that due to the charge soaking in; and second, to imperfect elasticity of the dielectric.  Speaking of the extraordinary rise of pressure on the Deptford mains, he said he had observed similar effects with other cables.  In his experiments the sparking distance of a 14,000 volt transformer was increased from 3/16 of an inch to 1 inch by connecting the cables to its terminals.  No difference was detected between the sparking distances at the two ends of the cable, nor was any rise of pressure observed when the cables were joined direct on the dynamo.

In his opinion the rise was due to some kind of resonance, and would be a maximum for some particular frequency.  Mr. Mordey mentioned a peculiar phenomenon observed in the manufacture of his alternators.  Each coil, he said, was tested to double the pressure of the completed dynamo, but when they were all fitted together, their insulation broke down at the same volts.  The difficulty had been overcome by making the separate coils to stand much higher pressures.  Prof.  Rucker called attention to the fact that dielectrics alter in volume under electric stress, and said that if the material was imperfectly elastic, some loss would result.  The president said that, as some doubt existed as to what Mr. Ferranti had actually observed, he would illustrate the arrangements by a diagram.  Speaking of condensers, he said he had recently tried lead plates in water to get large capacities, but so far had not been successful.