Page:February 1916 QST.djvu/11

28 to this condenser.

The insulating qualities of air are reduced by heating of the condenser plates and by reductions in the air pressure. If the plates are put in a vacuum, there is practically no dielectric between them.

In speaking of the vanishing metal, I think Kathis Kathkan referred to the light tinfoil in a condenser which is sometimes eaten away by the brushing of too high a voltage. Copper, brass, or aluminum will not eat away like the foil.

P. S. The typewriter is used by Americans because it is considered a much neater form of letter writing. Most men are not good penmen when in a hurry, so the typewriter is much faster than handwriting. I may also add that the hand writing of different men shows much of the character of the man and this is objectionable in some lines of business.

MR. ALLEN’S SOLUTION OF KATHKAN’S PROBLEM.

When a condenser is charged, one set of plates is charged positively and the other negatively. This fact gives rise to a tendency for a spark to pass between the plates and thus equalize the charge. The dielectric, however, prohibits the passage of a spark. Hence, there is a great pressure or stress on the dielectric.

Contrary to general opinion, the seat of the charge of a condenser is not in the plates. It is in the dielectric. This fact may be shown by the following experiment:

Charge a Leyden jar, made with movable coatings, and set is on an insulating stand. Lift out the inner coating and then, taking the top of the glass vessel in one hand, remove the outer coating with the other. Test the coatings with an electroscope and no charge will be found. Bring the glass vessel near a pile of pith-balls. They will be attracted to it, showing that the glass is electrified. Now build up the Leyden jar by putting the parts together. The jar may be discharged in the usual manner. This experiment shows conclusively that the seat of charge is in the dielectric. The same is true of any dielectric whether glass, mica, air, oil or paper. All dielectrics act similarly and so they are all subjected to a stress whenever a condenser is charged.

It would be impossible “to vanish” the air from a variable air dielectric condenser by blowing through it. Hence, there will always be some dielectric present. Since the dielectric contains the charge it is evident that the condenser will remain charged. If the condenser were placed in a vacuum, somewhat different results would take place, but it would require too much valuable space to explain these.

EDWIN B. ALLEN,     Westerly, R. I. 





'''In this aerial pole, Mr. Patch has a structure which has defined a great many winds. At present, as shown in the picture, the top section of the pole and the aerial itself are lowered for repairs.'''