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This will be apparent from another photograph which is marked XXVIII. In this instance the same connections were used as before, only the free terminal of the lamp was connected by a wire to the structure of iron pipes above. The wire can be scarcely distinguished. In this experiment resonance with the exciting circuit was obtained with 6 tanks on each side, this would mean a capacity of three tanks or 108 bottles = 108 x 0.0009 = 0.0972 mfd.

The inductance of the exciting circuit comprised a primary


turn with secondary short-circuited = 41,000 cm, as before, and all the turns of the regulating coil with connections, that is about 85,000 cm, giving total inductance at 41,000 + 85,000 = 126,000 cm or = $! {126 \over 10^{6}} $! henry. From this follows

$! {{2 \pi \over 10^{3}} \sqrt{0.0972 \times {126 \over 10^{6}}}} $! = $! {{2 \pi \over 10^{6}} \sqrt{12.2472}} $! = $! {{6.28 \times 3.5} \over 10^{6}} $! = $! {21.98 \over 10^{6}} $!


n = 45,496 or approx. 45,500 = n.

As will be seen from the consideration of the diagram above, in this experiment the entire energy supplied to the structure or capacity C had to pass through the lamp. Suppose the latter to consume 50 watts, and taking the capacity C with reference to previous estimates roughly at 500 cm. with the protecting hood, and designating with P again the potential to which the structure is charged, we have

50 = $! {{500 \over {9 \times 10^{11}}} \times {{p^{2} \times 45,500 \times 2} \over 2}} $! or P2 = $! {{9 \times 10^{8}} \over 455} $!


P = $! {{3 \times 10^{4}} \over \sqrt{455}} $! = $! {{3 \times 10^{4}} \over 21.3} $!

approx. or = 1409 volts = P, which is a very small pressure indeed. This pressure could have been, of course, still further reduced by using a resonating circuit of still higher frequency. In the manner just described and illustrated a great many lamps could have been lighted by the vibrations transmitted to the ground and some of the facts pointed out before will enable one to make an approximate estimate in this respect. However, by connecting the “extra coil” as in normal operation, that is, to the free end of the secondary instead of to the ground, a number of lamps might have been lighted corresponding to the full output of the oscillator, say, one thousand lamps or more. Even through the ground, as in the experiment described, the action of the exciting circuit was so intense that the current of the supply transformers had to be cut down to but a very small fraction of the current taken by full output.

It should be remarked that also in the experiment described before (Plate XXVII.) a considerable number of lamps might have been lighted, but not nearly as many as in the case presently described, owing to the very small capacity of the lamps, as before stated.

Phot. XXVIII. An incandescent lamp lighted by the current passing from "extra coil" to the structure of iron pipes. The lower end of the coil is connected to the ground plate.


Lowercase tau - an irrational constant defined as the ratio of the circumference of a circle to its radius, equal to the radian measure of a full turn; approximately 6.283185307 (equal to 2π, or twice the value of π).
A natural rubber material obtained from Palaquium trees, native to South-east Asia. Gutta-percha made possible practical submarine telegraph cables because it was both waterproof and resistant to seawater as well as being thermoplastic. Gutta-percha's use as an electrical insulator was first suggested by Michael Faraday.
The Habirshaw Electric Cable Company, founded in 1886 by William M. Habirshaw in New York City, New York.
The Brown & Sharpe (B & S) Gauge, also known as the American Wire Gauge (AWG), is the American standard for making/ordering metal sheet and wire sizes.
A traditional general-purpose dry cell battery. Invented by the French engineer Georges Leclanché in 1866.
Refers to Manitou Springs, a small town just six miles west of Colorado Springs, and during Tesla's time there, producer of world-renown bottled water from its natural springs.
A French mineral water bottler.
Lowercase delta letter - used to denote: A change in the value of a variable in calculus. A functional derivative in functional calculus. An auxiliary function in calculus, used to rigorously define the limit or continuity of a given function.
America's oldest existing independent manufacturer of wire and cable, founded in 1878.
Lowercase lambda letter which, in physics and engineering, normally represents wavelength.
The lowercase omega letter, which represents angular velocity in physics.