This is an active site

It originated  in -

Is supported by two specialised sites and

Pages on these sites are being added as our ideas develop. 

The Headings are recent articles

The draw-down pages are supplementary articles written over the years.

Throughout the websites, we give a note where pages have been written by a third party.

Otherwise pages, sketches and diagrams have been produced by the authors of the site

Where the article is date-sensitive, the date of origin is given.