Feed Line No. 9
NOT SO ORIGINAL AFTER ALL
by Gary Peterson
For those who believe the
2006 MIT "Witricity" demonstration was the first of its kind, look at this
illustration from "Tesla Apparatus and Experiments—How to Build Both Large
and Small Tesla and Oudin Coils and How to Carry On Spectacular Experiments
With Them," by H. Winfield Secor, Practical Electrics, November 1921.
An experiment showing the action of the A. C.
transformer and which can be performed with high frequency currents is shown
at Fig. 11 above. Two coils of wire about 24" in diameter, are constructed
with the number of turns indicated in the diagram. When the primary is
connected to the condenser and the spark gap, as shown, the 110 volt 16 C.
P. or a 40 watt lamp connected to the secondary, will light up even when the
primary and secondary coils are separated a distance of 1 foot or more,
depending upon the size of the transformer or spark coil used for the
And then there is this drawing
and accompanying description from the lecture "High
Frequency Oscillators for Electro-therapeutic and Other Purposes,"
Electrical Engineer, November 17, 1898 of a similar apparatus constructed by
"When it is desired to use small currents of
high tension, a secondary coil is resorted to, as illustrated in Fig. 2. I
have found it from the outset convenient to make a departure from the
ordinary ways of winding the coils with a considerable number of small
turns. For many reasons the physician will find it better to provide a large
hoop H of not less than, say three feet in diameter and preferably more, and
to wind upon it a few turns of stout cable P. The secondary coil S is easily
prepared by taking two wooden hoops h h and joining them with stiff
cardboard. One single layer of ordinary magnet wire, and not too thin at
that, will be generally sufficient, the number of turns necessary for the
particular use for which the coil is intended being easily ascertained by a
few trials. Two plates of large surface, forming an adjustable condenser,
may be used for the purpose of synchronizing the secondary with the primary
circuit, but this is generally not necessary. In this manner a cheap coil is
obtained, and one which cannot be easily injured. Additional advantages,
however, will be found in the perfect regulation which is effected merely by
altering the distance between the primary and secondary, for which
adjustment provision should be made, and, furthermore, in the occurrence of
harmonics which are more pronounced in such large coils of thick wire,
situated at some distance from the primary."
MIT WiTricity—not so original after all.
Front row: Prof. Peter Fisher and Robert Moffatt;
second row: Prof. Marin Soljačić;
third row: Andre Kurs, Prof. John Joannopoulos and Aristeidis Karalis.