Kerr was not just a theoretician; he was an experimentalist. He authored the first edition of Optical Mineralogy in 1943, with subsequent editions released in 1959 and 1977. The third edition (published by McGraw-Hill) remains the gold standard. His approach was distinctly practical—lenses, stage techniques, and interference figures were described with the clarity of a master teacher who had spent thousands of hours at the microscope.