In addition to his overall structural problem of how to support
the weight of the lantern tower, a s I see it, the Master Carpenter
is trying to solve several subsidiary problems, one of which is to be seen
in this detail : There are no less than 13 joists, major and minor, which
must come together at a single point ("A").
This detail of one of the eight primary joint confluences at
the "floor" (as Hewett terms it --the wooden vaults are below,
the lantern tower above) level of the Ely Octagon illuminates part of
the complexity of design which was necessary to construct this extraordinary
Note that all of the secondary and tertiary beams ("joists"
as it were, since this may be called a "floor") conververge,
ultimately, upon the single vertical beam/"pilaster," "A."
That is, all of the weight/stress of all of these elements
(as well as those of the wall beams, "f") was carried
to the ground via the vertical beam "A" except
for that which was carried by the wooden ribs below.
If this stress was essentially carried by the beams/joists which we
see here, then an examination of the type of joints used should suffice
to demonstrate this. The question then becomes : What
is the nature of these joints?
Since, in any wooden joint, grain is an essential
element, I've added some lines to emphesize the direction of the grain
in these beams, together with shading to clarify the upper surfaces.