Experiments with Alternate Currents of High Potential and High Frequency | Page 8

course out of the question, in an experimental lecture, with only

a few minutes at disposal for the performance of each experiment, to
show these discharge phenomena to advantage, as to produce each
phenomenon at its best a very careful adjustment is required. But even
if imperfectly produced, as they are likely to be this evening, they are
sufficiently striking to interest an intelligent audience.
Before showing some of these curious effects I must, for the sake of
completeness, give a short description of the coil and other apparatus
used in the experiments with the disruptive discharge this evening.
[Illustration: FIG. 3.--DISRUPTIVE DISCHARGE COIL.]
It is contained in a box B (Fig. 3) of thick boards of hard wood,
covered on the outside with zinc sheet Z, which is carefully soldered all
around. It might be advisable, in a strictly scientific investigation, when
accuracy is of great importance, to do away with the metal cover, as it
might introduce many errors, principally on account of its complex
action upon the coil, as a condenser of very small capacity and as an
electrostatic and electromagnetic screen. When the coil is used for such
experiments as are here contemplated, the employment of the metal
cover offers some practical advantages, but these are not of sufficient
importance to be dwelt upon.
The coil should be placed symmetrically to the metal cover, and the
space between should, of course, not be too small, certainly not less
than, say, five centimetres, but much more if possible; especially the
two sides of the zinc box, which are at right angles to the axis of the
coil, should be sufficiently remote from the latter, as otherwise they
might impair its action and be a source of loss.
The coil consists of two spools of hard rubber RR, held apart at a
distance of 10 centimetres by bolts c and nuts n, likewise of hard rubber.
Each spool comprises a tube T of approximately 8 centimetres inside
diameter, and 3 millimetres thick, upon which are screwed two flanges
FF, 24 centimetres square, the space between the flanges being about 3
centimetres. The secondary, SS, of the best gutta percha-covered wire,
has 26 layers, 10 turns in each, giving for each half a total of 260 turns.
The two halves are wound oppositely and connected in series, the

connection between both being made over the primary. This disposition,
besides being convenient, has the advantage that when the coil is well
balanced--that is, when both of its terminals T_1 T_1 are connected to
bodies or devices of equal capacity--there is not much danger of
breaking through to the primary, and the insulation between the
primary and the secondary need not be thick. In using the coil it is
advisable to attach to both terminals devices of nearly equal capacity,
as, when the capacity of the terminals is not equal, sparks will be apt to
pass to the primary. To avoid this, the middle point of the secondary
may be connected to the primary, but this is not always practicable.
The primary PP is wound in two parts, and oppositely, upon a wooden
spool W, and the four ends are led out of the oil through hard rubber
tubes tt. The ends of the secondary T_1 T_1 are also led out of the oil
through rubber tubes t_1 t_1 of great thickness. The primary and
secondary layers are insulated by cotton cloth, the thickness of the
insulation, of course, bearing some proportion to the difference of
potential between the turns of the different layers. Each half of the
primary has four layers, 24 turns in each, this giving a total of 96 turns.
When both the parts are connected in series, this gives a ratio of
conversion of about 1:2.7, and with the primaries in multiple, 1:5.4; but
in operating with very rapidly alternating currents this ratio does not
convey even an approximate idea of the ratio of the E.M.Fs. in the
primary and secondary circuits. The coil is held in position in the oil on
wooden supports, there being about 5 centimetres thickness of oil all
round. Where the oil is not specially needed, the space is filled with
pieces of wood, and for this purpose principally the wooden box B
surrounding the whole is used.
The construction here shown is, of course, not the best on general
principles, but I believe it is a good and convenient one for the
production of effects in which an excessive potential and a very small
current are needed.
In connection with the coil I use either the ordinary form of discharger
or a modified form. In the former I have introduced two changes which
secure some advantages, and which are obvious. If they are mentioned,

it is only in the hope that some experimenter may