In “The Cause of an Ice Age” Sir R. Ball claims to have removed from the Astronomical Theory of Glaciation the greatest stumbling block in the way of its general acceptance, and to have placed it on a firm and unassailable foundation. And this stumbling block he considers to have been Sir J. Herschel's erroneous statement, that, of the total heat received by a hemisphere in a year, one-half is received during the summer, and the other half dining winter.