Re: early rotary gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

"Original poster: "Steve Cook" <steve-at-g8cyerichmond.freeserve.co.uk>

I actually saw a model boat, which from memory was based largely on the
principles of this patent, it was on exhibition in the London Scence
Museum
many years ago. Individual circuits were controlled by a rotary
commutator
based on a wooden cotton reel with nails as contacts. The coherer was a
Branly-Lodge type. I believe the model was built somewhat prior to the
1914-18 war."

	Last time I was there was in 1991 and don't remember it, but didn't
have a chance to see everything.  I have a radio-controlled bus using a
spark transmitter and a coherer receiver which was built in the late
1950's.  Part of a whole line of Japanese toys based on this simple
principle; they are now "collectibles" and selling for ridiculous
prices.  The first toys of the line used a battery-powered spark coil
but the last ones had a transmitter using a piezoelectric HV generator
similator to those used for lighting gas devices now.

	Over 50 years ago I worked in the Washington, DC area and used to visit
the Library of Congress reading room.  One of the first things I tried
to research was RC devices and found a British book circa 1918 which
described a radio-controlled dirigible working in a similar fashion.
Use of spark transmitters and coherers to actuate a relay and do
something goes back a long way, so what Tesla was really offering new
was the equipment following the receiver.  As I recall the patent
includes a description of his method preparing the material for the
coherer which indicates he must have experimented with different types
until he got a "sensitive device" which satisfied him.  I also seem to
remember that this particular device was not tuned but that he mentions
that tuning the transmitter and receiver would improve performance.

Ed