Subject: Who invented the magnetic stirrer?

My grandfather (Eddie McLaughlin) always claimed that he had 
invented the magnetic stirrer.
I'm getting more certain that he was right, but want to keep
checking whether anyone else knows of an inventor of this handy
device. I'm sure he had an original idea when he put the things
together but did someone else have the idea first?
He told me that while he was working as a research chemist in
Greenock, Scotland, (just before or just after WWII, he wasn't clear)
he had some small bar magnets coated with plastic so that by putting
them into a solution the plastic-coated magnets would not react with
the solution while being driven round by a motorised second magnet
under the container.
He was working for the MoD at the time, and so could not get a
patent personally. Eventually a rep from a chemical equipment
supplier spotted the devices (he had rigged up six in a row to perform
six titrations simultaneously) and shortly after that they were being 
marketed.
Are there any other claims to this invention?

Re: Who invented the magnetic stirrer?