Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 413

time. In eight patents⁽²⁷⁾ Tesla gives designs for rotary interrupters with conducting or conducting and insulating fluids, usually mercury and oil, respectively. In some designs the interruption takes place in an inert gas under pressure. He gives ingenious designs for using a mercury jet playing on a toothed metal rotor, and for producing two mercury jets (fluid contact).

The rotary interrupter with two auxiliary air gaps shown in the figure was a new idea. One of the reasons Tesla added these air gaps was probably the high voltages with which he was working, since they allowed him to regulate the excitation. That this could be done may be seen from the statement that by adjusting these gaps the period of charging from the secondary of the mains transformer could be shortened. At the end of the entry he records that the best results were obtained with two rotary interrupters (with toothed disks) rotating in opposite directions. He does not explain how he chose the tooth ratio so that the number of interruptions was equal to the product of the number of teeth.

July 28

This entry provides one of the most detailed descriptions of the receiver with two rotating coherers and a condenser for accumulating the energy from weak signals. At point b the circuit C - P is periodically made and broken and the resulting AC pulses bias sensitive device A' in the secondary. Sensitive device A is still poorly conducting so the charging current of C via damping coil L is small. When an arriving electromagnetic wave reduces the resistance of A, C charges much faster and the voltage induced in secondary S also rises rapidly. The resistance of A' drops rapidly and current from battery B' activates relay R. Judging by Tesla's report, the receiver was very sensitive to distant electrical discharges.

July 29

To check out his theoretical conclusions about the free oscillation of the “extra coil” (see 30 June and 26 July) Tesla made a new coil with a higher inductance. As this was his first experiment with the new coil, he had to adjust the circuit parameters by trial and error.

Tesla's ingenuity found full expression in the way in which he developed condensers for high voltages. He filed a patent application on his design for a fluid electrolyte condenser on June 17th 1896⁽⁶⁷⁾.

July 30

To try and verify his hypothesis about the rejection of harmonics with appropriate coils, Tesla changed the connection of his “extra coil” as shown in Figs. 4 and 5. To understand his way of proceeding one must take into account his ideas from 1893⁽⁶⁾ concerning the induction of earth currents via an aerial-earth system. However, the standing waves in terms of which he tried to explain the arcing over the lightning arresters cannot be significant at these frequencies.

July 31

Tesla made the condensers for the primary circuit out of mineral water bottles filled with a saturated solution of rock salt, and standing them in a metal tank of the same solution, thus creating a condenser bank with one common plate. The other plates (the