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 interested in. The sketch
of Ludwig Boltzmann, in the German language, contains a most powerful
and deep-going survey of the scientific work of this genius. In several
places the character of the man's personality rather than that 0/ the
scientist reveals itself, his attitude towards various problems and his
personal views. In his first address he refers to the value of
mathematics, we hear his dislike lor too vivid visual speculations and
crude hypotheses, his taste lor the soberness of mathematical formulae,
where he argues that the fundamental principles must needs escape
further explanation. On page 54 we read what he said about determin-
ism, and on page I8I he expresses himself on the relation of matter and
mind. His intimate feelings on space and time, and the aether, are
touched upon on pages 240, 26I, 274.
