"The mathematics that physicists find useful is precisely that which describes the geometry of space and time.
The Geometric Algebra (Clifford Algebra), which it defines, is the most powerful and general language available for the development of mathematical physics."
Here are bootleg scans of my copies of the OHP slides from the original lecture in 1989.
Subsequently the lecture was expanded into a paper, with some
alterations and rearrangements.
A full
postscript
version of that paper is available from
Geometric Algebra
Group's server in Cambridge,
as is the latex-to-html conversion behind the links below.
The main sections, with links to the most nearly corresponding OHP slides:
James Heald, June 1996