With the present ninth volume we bring to a conclusion the edition of the Collected Papers of Professor H. A. Lorentz. It contains the evidence of his constant activity to promote the interest in science of a larger public, in particular of his country men, by addresses on se veraloccasions, by articles in magazines and newspapers, and other wise. In a certain way in this part of his work he belongs more partic ularly to his country, therefore we reproduce it in the original lang uage, with the exception of his inaugural address as Leiden professor early in I878, which readers abroad might be...