Nikola Tesla Books
Books written by or about Nikola Tesla
Data for calculating inductance
diameter of coil d = 10 5/16" = 10.3125" = 26.19 cm.
$! {S = {{\pi \over 4} d^{2}} = {0.7854 \times 685.9} = 538.7} $! cm. sq. N = 550
l = 41.25" = 104.77 cm. N2 = 302,500
$! {L = {{4 \pi \over l} N^{2} \, S} = {{12.5664 \times 302,500 \times 538.7} \over 104.77} = 12.5664 \times 302,500 \times 5.14} $!
L = 19,538,800 cm. or 0.019539 henry approx.
following readings to measure the inductance were taken:
| E | I | ω | R | average of three readings practically the same. |
| 117 | 6.2 | 880 | 9.586 |
From these data
$! {{E \over I} = {117 \over 6.2}} $! = 19 approx.$! {\left(E \over I\right)^{2} = 361} $! $! {R^{2} = 91.89} $!
$! {{\left(E \over I\right)^{2} - R^{2} = 269.11}} $!
$! {L = {\sqrt{269.11} \over 880} = {16.41 \over 880}} $! or
L = 0.01865 henry = 18,650,000 cm.
Colorado Springs
Sept. 11, 1899
Experiments were continued with apparatus before described and the effects outside at a distance investigated, the chief object being to establish nodal points on earth’s surface. The transmitting apparatus was one giving more rapid vibrations and was improvised as indicated in the left sketch.
The apparatus for investigation comprised the ten” drum, before referred to, wound with 395 turns wire No. 18 B. & S. and to increase magnifying factor another layer was wound on top, thus doubling the section. It was found that the scheme of double windings is not a good one because the e.m.f. in both wires are apt to be unequal and it is more difficult to make adjustment. The connections of apparatus were as indicated in the right sketch.
183
September 11
Tesla probably thought that he would more easily detect standing waves in the vicinity of the laboratory if the wavelength was shorter. He assumed that the ball-cable system would produce waves which could be registered by the receiver. However, although he measured the electromagnetic field up to a mile away, he probably did not find the expected variation, and could only conclude that electrical disturbances were registered.
September 11
He continued the experiments started two days ago with the intention of finding the nodes in the ground waves. He adjusted the oscillator to produce waves of somewhat higher frequencies than common ones, probably with the intention to get nodes of "standing" waves in the ground closer to the laboratory. The electromagnetic field he measures with the apparatus in Fig. 2, very slightly changed with relation to the previous one (please see Sept. 5, Fig. 3). Although he registered a signal at one mile distance from the laboratory, he does not mention how the signal varied with regard to distance.
