Scientific American Supplement, No. 795, March 28, 1891 by Various
page 56 of 136 (41%)
page 56 of 136 (41%)
![]() | ![]() |
|
only took place when transformers were used, and not when the dynamos
were connected direct. In the former case the increase of volts was proportional to the length of main used, and 8,500 at Deptford gave 10,000 at London. 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 |
|