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Nikola Tesla: Colorado Springs Notes, 1899-1900Page 250

October 31, 1899

Oct. 31, 1899

Measurement of inductances: New coil for further investigating effect of altitude upon capacity of body connected to earth.

The drum of 14" diam. and 8 feet long was again used, the cord No. 20 being taken off and wire No. 10 rubber-covered used instead. Most of the data from before remained, only the number of turns was reduced from 689 to 346.

The readings of e.m.f., current and frequency were as follows:

E I ω
85 15.635 880
84.75 15.6
82.5 15.3
Average values:
84.38 15.512 880
R
coil with cord 1.752
cord 0.596
coil alone 1.156 ohm.

This gives: $! {{E \over I} = 5.44}$!   $! {{\left({E \over I}\right)^{2}} = 29.5936}$!

R2 = 1.3364
ω2 = 774,400

L2 = $! {{{\left({E \over I}\right)^{2} - R^{2}} \over ω^{2}} = {{29.5936 -1.3364} \over 774,400} = {28.2572 \over 774,400}}$! henry = 0.00003649

or L = $! {\sqrt{0.00003649}}$! = 0.00604 H or L = 6,040,00 cm.

Now for calculating with reference to note Oct. 18 we have the following data:

 diam. of core 14" = 35.5 cm length of core 96" = 243.84 cm = lS = 1000 sq. cm.N = 346N2 = 119,716 L = $! {4 \pi \over l}$! N2S = $! {{12.5664 \times 119,716,000} \over 243.84}$! From this L = 6,169,600 cm or 0.00617 henry approx. This is nearly 2% greater than measured value - fairly close.

250

Glossary

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 &amp; Sharpe (B &amp; 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&nbsp;angular velocity in physics.&nbsp;