Re: coherers

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

> >         It 'decoheres' due to power removal (like an SCR) rather
> >
> >         than thru mechanical action.
> >         Do classic coherers decohere on removal of power?
> >         My recollection is they do...
> 
> My coherers don't. They also "cohere" without DC bias across them.
> They change resistance once triggered, and keep the condition until
> being shaken.
> But there were coherers that would decohere spontaneously some time
> after triggered, without need of tapping. Some old texts mention
> a kind of coherer used by the Italian navy that had this property.
> 
> Antonio Carlos M. de Queiroz

	The "Italian Navy Coherer" used a rotating wheel dipping into the
surface of a small pool of mercury, which had oil on the top to keep it
from oxidizing.  I've always intended to make one and see if it work,
but haven't yet gotten enough ambition.  There's been a lot of
discussion concerning Marconi's possible patent infringement, as he used
them in some of his early work.

	On the subject of "old wireless" stuff, here's a question for Antonio:

Have you ever built a "magnetic detector"?  I've read of them a lot, but
have never seen a single statement about their sensitivity.  They were
reported as "less sensitive than a coherer" [if that is possible] but
much more stable, and were standard Marconi equipment for several
years.  I've always wanted to make one but can't find the fine,
insulated iron wire.

Ed