Unpublished letter, regarding theory of pyramids from John Walsh to Davies Gilbert Walsh illustrates a geometrical example in an effort to establish a theory of pyramids that does not rely on the theory of exhuastions. An ink inscription final page verso reads 'Not to be read'. Subject: Mathematics Written by Walsh in Leitrim Street, Cork [Ireland] and addressed to Gilbert in Bridge Street, Westminster, London. Postmarked 21 and 23 November 1830. 19 November 1830