# [r-t] Fwd: "double" cambridge?

Richard Smith richard at ex-parrot.com
Sun Jan 31 15:25:02 UTC 2010

```Philip Earis replied, quoting Edward Martin:

> "Could someone please give me details of what was used in
> 1752? and how do we know? I cannot find reference in any
> of the 18th century books to which I have access"
>
> From www.methods.org.uk (at the end of the plain major collection):
>
> Eastern Bob -14-38-18-18-18-18-18-12 b 27.12.1747 Shoreditch  59/67
> Double Eastern Bob -14-38-18-78-58-16-18-12 d 12.1.1752 Westminster, St Margaret  59/67

Or with two (marginally) more familiar methods:

Union         3.1.7.1.7.1.7.1.7.1.7.1.5.1 1256734
1728-02-17   Lawrence Jewry   RW 58/767

Double Union  3.1.7.1.7.3.7.5.7.1.7.1.5.1 1273456
1771-03-01   Leeds, Yorks     RW 58/767

Edward Martin wrote:

> RAS's response has me very puzzled...  I respect his
> opinions but why is it that when he asks: "Can you think
> of any methods that were called 'Double' but that did not
> have glide symmetry, then?  I'm not aware of any."

I think perhaps I wasn't very clear.  I meant that all of
the examples I knew included glide symmetry amongst the
symmetries possessed by the method.  Most methods named
'Double', Double Norwich to take a concrete example, have
three symmetries: palindromic, glide and rotational.

Modulo a few subtleties regarding mirror symmetry, it is
possible to prove that if a method possesses any two of
these three symmetries, then the third must also be present.
However, as Phil's website shows, it is possible to have any
a method one of the symmetries individually.

Lots of pre-20th century methods have just palindromic
symmetry -- Plain Bob, Grandsire and Stedman, to pick three
of the commonest.  So far as I know, none of these are
called 'Double'.  A small number have just glide symmetry,
and so far as I know they are all called 'Double'.  I know
of no pre-20th century rotationally symmetric methods.

However, we should be careful relying on the methods
collections as reliable sources as to the names of
historical methods.  Historically, the Methods Committee
hasn't been beyond a bit of revisionism when it comes to
methods names.  So I would be interested in knowing how the
contemporary sources actually referred to these methods.

> Actually I can find no examples of glide symmetry in 18th
> cent books at all, but I have found both palindromic &
> non-palindromic methods each with 'double' in their title

I would be interested in some examples of non-palindromic
methods with 'Double' in their title.  The only two pre-20th
century examples that I'm aware of are Double Eastern and
Double Union.  (Double Newark and Double Wollaton Doubles
could count, but I've not seen any evidence of these being
pre-20th century.)  All of these have glide symmetry.

RAS

```