The title of this Series of Essays—_Half Hours with Modern Scientists_—suggests a variety of thoughts, some of which may not be inappropriate for a brief introduction to a new edition. _Scientist_ is a modern appellation which has been specially selected to designate a devotee to one or more branches of physical science. Strictly interpreted it might properly be applied to the student of any department of knowledge when prosecuted in a scientific method, but for convenience it is limited to the student of some branch of physics. It is not thereby conceded that nature, _i.e._, physical or material nature is any more legitimately or exclusively the field for scientific enquiries than spirit, or that whether the objects of science are material or spiritual, the assumptions and processes of science themselves should not be subjected to scientific analysis and justification. There are so-called philosophers who adopt both these conclusions. There are those who reason and dogmatize as though nature were synonymous with matter, or as though spirit, if there be such an essence, must be conceived and explained after the principles and analogies of matter;—others assume that a science of scientific method can be nothing better than the mist or moonshine which they vilify by the name of metaphysics. But unfortunately for such opinions the fact is constantly forced upon the attention of scientists of every description, that the agent by which they examine matter is more than matter, and that this agent, whatever be its substance, asserts its prerogatives to determine the conceptions which the scientist forms of matter as well as to the methods by which he investigates material properties. Even the positivist philosopher who not only denounces metaphysics as illegitimate, but also contends that the metaphysical era of human inquiry, has in the development of scientific progress been outgrown like the measles, which is experienced but once in a life-time; finds when his positivist theory is brought to the test that positivism itself in its very problem and its solutions, is but the last adopted metaphysical theory of science.