Ok, so I looked at my Spiers jack.  At first glance it appeared to be
bedded at 45 deg.  So I went to a Brown and Sharp proctrator and tried
again. 47 deg!  However, the blade, a tapered blade that appeared to have
been in place for a good long time, was ground to a fairly low angle bevel.
Makes me wonder if, due to the thickness of the blade, if you could get
away with a lower angle bevel than you would with a thin, modern blade.

Then again, Spiers probably did not use a Brown and Sharp protractor.  How
about this?  All English infill planes are descended from one common
ancestor. This ancestral plane was bedded at 47 deg, for an arcane reason
known to and understood only by a past great master.  Far be it for us
lowly modern neanderthals to attempt to understand the true meaning of 47
degrees.

Don't worry, I'll ask my spirit guide tonight for enlightment.

Gary Roberts 
Boston, MA
My opinions are my own.  At least I think they are.