Pictured Puzzles and Word Play / A Companion to the Twentieth Century Standard Puzzle Book - A. Cyril Pearson

The enigma—

I lose my head when I am here,
Transpose me I am three;
Look in a book, you find me there,
And with me her and he—

is solved by There.

Jack did declaim that he could square
The circle to a decimal;
His friends claimed that a brain so rare
Required attention medical.

The words in italics are spelt with the same letters.