ould not, by far, equal the magnificent display of streams and
sparks obtained from such a disruptive discharge coil when properly
adjusted. To give an idea, a coil such as the present one will cover
easily a plate of 1 metre in diameter completely with the streams. The
best way to perform such experiments is to take a very thin rubber or
a glass plate and glue on one side of it a narrow ring of tinfoil of
very large diameter, and on the other a circular washer, the centre of
the latter coinciding with that of the ring, and the surfaces of both
being preferably equal, so as to keep the coil well balanced. The
washer and ring should be connected to the terminals by heavily
insulated thin wires. It is easy in observing the effect of the
capacity to produce a sheet of uniform streams, or a fine network of
thin silvery threads, or a mass of loud brilliant sparks, which
completely cover the plate.

Since I have advanced the idea of the conversion by means of the
disruptive discharge, in my paper before the American Institute of
Electrical Engineers at the beginning of the past year, the interest
excited in it has been considerable. It affords us a means for
producing any potentials by the aid of inexpensive coils operated from
ordinary systems of distribution, and--what is perhaps more
appreciated--it enables us to convert currents of any frequency into
currents of any other lower or higher frequency. But its chief value
will perhaps be found in the help which it will afford us in the
investigations of the phenomena of phosphorescence, which a disruptive
discharge coil is capable of exciting in innumerable cases where
ordinary coils, even the largest, would utterly fail.

Considering its probable uses for many practical purposes, and its
possible introduction into laboratories for scientific research, a few
additional remarks as to the construction of such a coil will perhaps
not be found superfluous.

It is, of course, absolutely necessary to employ in such a coil wires
provided with the best insulation.

Good coils may be produced by employing wires covered with several
layers of cotton, boiling the coil a long time in pure wax, and
cooling under moderate pressure. The advantage of such a coil is that
it can be easily handled, but it cannot probably give as satisfactory
results as a coil immersed in pure oil. Besides, it seems that the
presence of a large body of wax affects the coil disadvantageously,
whereas this do