Nikola Tesla Books
Books written by or about Nikola Tesla
Now to secure resonance with structure attached and under best working conditions of the exciting system with possibly only a very few turns of the regulating coil in primary, we have from above to reduce inductance of extra coil by a ratio of $! {22,650 \over 76,150} $!. For same length turns will be
$! {\sqrt{{2265 \over 7615}}} $! x 100 = 54 - 55 t.
Colorado Springs
Dec. 14, 1899
Test to ascertain free vibration of new “Extra Coil System” (latest)
The new “extra coil” latest type is wound on same frame 8' 3" diam. and 8 feet in length, the wire being this time No. 6 instead of wire No. 10 as before. There are presently just 100 turns. A coil of No. 6 wire wound on drum 14" diam. and 8 feet long, which was used repeatedly before, was connected in series with this latest extra coil and resonance determined by means of the adjustable small inductance as usual and a miniature lamp shunting the turns. The results with no capacity on the terminal which was “free” were:
| Capacity in primary circuit | Inductance in primary circuit |
| $! {{5 \times 36} \over 2} = $! {180 \over 2} $! = 90 bottles = 0.081 mfd | One primary turn (two cables in multiple) + 3 turns regul. coil |
When a ball 30" diam. with 4 feet of wire was connected to the free terminal the readings were:
| Capacity-primary: 0.081 mfd | Inductance-primary: as above, only 7 1/2 turns in regul. coil. |
In both cases the excitation was effected through the secondary of the oscillator from a point of the same 3/4 turns from ground plate. In the first case the inductance of primary, taking into consideration the secondary reaction, is estimated at 41,000 cm. Adding to this the inductance of connections and 3 turns of regulating coil = 10,000 cm the total inductance was about 51,000 cm. This with a capacity of 0.081 mfd would give the period of the system comprising the two coils in series
Ts = $! {{2 \pi \over 10^{3}} \sqrt{0.081 \times {51 \over 10^{6}}}} $! = $! {2 \pi \over 10^{6}} $! x 2.03 = $! {12.75 \over 10^{6}} $! approx. and n = 78,500
approx. per second. When the capacity of a ball of 30" diam. is associated with the system we have the inductance of the primary circuit, as before, 41,000 cm for the primary turn with secondary reacting plus 7 1/2 turns regulating coil and connections=23,580 cm, with reference to the table, that is, total=64,580 cm. The period in the second case was therefore
Ts = $! {{2 \pi \over 10^{3}} \sqrt{0.081 \times {6458 \over 10^{8}}}} $! = $! {{2 \pi \over 10^{7}} \sqrt{523.098}} $! = $! {{6.28 \times 22.9} \over 10^{7}} $! = $! {143.8 \over 10^{7}} $!
318
December 14
He tests a new "additional coil by using previously described resonant methods (please see Dec. 3). He includes in the oscillator circuit the resonant transformer, and the "additional" coil excites via secondary terminals. The estimate of operating frequency he obtains by calculation on the basis of ''reduced primary inductance'' and capacitance in the primary circuit. On the basis of undefined "reduction of primary inductance" (please see the remark along with the comment on Dec. 5), all results are, as Tesla himself says, rough approximations of accurate results.
