Silent practice apparatus

[John Harrison]

This came up on ChangeRingers, but no one there gave an authoritative
answer about the pedigree.  Maybe the historians will know.

I have always believed that Seage's apparatus, aka ting tangs, were a
single species, but it turns out that they are not.  The mechanism
invented by Epaphras Seage in Devon, and installed in several Devon towers
is shown about 4/5 down the page here:  
http://groups.exeter.ac.uk/gdr/rrd/mar08/rrd.html

The mechanisms installed in several Berkshire towers, notably Twyford where
they are intact and working, are operated by a chain round the headstock,
rather than a rocker arm.  Alistair Donaldson and I recently took pictures,
which you can see at:
 
You can see the mechanism at:
http://jaharrison.me.uk/Temp/SilentPractMech.jpg 

The chain hooks onto a loop on the bell side of the headstock, seen with
the bell up at:  

http://jaharrison.me.uk/Temp/SilentPractHSUp.jpg 

To disengage the mechanism, unhook the chain and hook it onto the adjacent
loop on the bell frame, see with the bell down at:

http://jaharrison.me.uk/Temp/SilentPractHSDown.jpg 

David Sullivan suggested that this might have been a Whitechapel design,
installed before the first war.  Can anyone confirm or deny that?  And are
these the only two variants, or are there others?

Regards

-- 
John Harrison
Website http://jaharrison.me.uk