high freq ttenoy and high po tentia l chrrente i si

student, but their description would lead me too far from theprincipal subject. Partly for this reason, and partly on accountof their vastly greater importance, I will confine myself to thedescription of the light effects produced by these currents.

In the experiments to this end a high tension induction coil orequivalent apparatus for converting currents of comparativelylow into currents of high tension is used.

If you wall be sufficiently interested in the results I shall de-scribe as to enter into an experimental study of this subject; if youwill be convinced of the truth of the arguments I shall advance—your aim will be to produce high frequencies and high potentials •in other words, powerful electrostatic effects. You will then en-counter many difficulties, which, if completely overcome, wouldallow us to produce truly wonderful results.

First will be met the difficulty of obtaining the required fre-quencies by means of mechanical apparatus, and, if they be ob-tained otherwise, obstacles of a different nature will presentthemselves. Next it will be found difficult to provide the requi-site insulation without considerably increasing the size of theapparatus, for the potentials required are high, and, owing to therapidity of the alternations, the insulation presents peculiar diffi-culties. So, for instance, when a gas is present, the dischargemay work, by the molecular bombardment of the gas and con-sequent heating, through as much as an inch of the best solidinsulating material, such as glass, hard rubber, porcelain, sealingwax, etc.; in fact, through any known insulating substance. Thechief requisite in the insulation of the apparatus is, therefore, theexclusion of any gaseous matter.

In general my experience tends to show that bodies whichpossess the highest specific inductive capacity, such as glass,afford a rather inferior insulation to others, which, while they aregood insulators, have a much smaller specific inductive capacity,such as oils, for instance, the dielectric losses being no doubtgreater in the former. The difficulty of insulating, of course,only exists when the potentials are excessively high, for withpotentials such as a few thousand volts there is no particular diffi-culty encountered in conveying currents from a machine giving,say, 20,000 alternations per second, to quite a distance. Thisnumber of alternations, however, is by far too small for manypurposes, though quite sufficient for some practical applications.This difficulty of insulating is fortunately not a vital drawback ;