ALTHOUGH physics is one of the oldest and most respectable of the sciences, it must be acknowledged with regret that many otherwise well-educated persons have but a vague idea of its scope, and the question, "What is a physical laboratory and what does one do in it?" is by no means a rare one. The science of physics or natural philosophy, as it was called by Newton, properly includes the study of all natural phenomena that are not concerned with life, as distinguished from biology, which undertakes to investigate the phenomena of living organisms. To speak more particularly, physics deals with mechanics or the phenomena of motion and its causes, including those motions which we characterize as sound; with heat, light, electricity and magnetism and those new phenomena which have to do with radio-activity and the recently discovered new sorts of radiation. It is thus impossible to make any classification of physics which shall exclude astronomy, which is divided into celestial mechanics or the study of the motions of the sun, planets, comets and stars, and the new science of astrophysics, or the study of the physical and chemical constitution of the stars mainly by means of the spectroscope invented only about fifty years ago, or which shall exclude chemistry, which now more than ever before is concerning itself with the relations of different elements and their compounds to phenomena of heat, electricity and light. Geology has mainly to do with the applications of physics to the surface of the earth. Nevertheless, for purposes of convenience it has become customary to divide off these other sciences from physics proper and to have them studied and taught by separate professors.
If we examine the history of physics we shall find that this division