Hill, it is wide and beautiful essay of Mayer's, entitled 'Beitraege zur Dynamik des Himmels,' Heilbronn, 1848; 'Bemerkungen ueber das Mechanische Equivalent der Waerme,' Heilbronn, 1851. ==================== IN MEMORIAM.--Dr. Julius Robert Mayer and James Prescott Joule. In his criticism.