PHYSICS (from Gk. cbucroof, physika, nom. pl. lieu. of otm6s, physikos, relating to nature). one successors of the study formerly called natural philosophy. or the science of the phenomena of nature as revealed to us by our senses and as interpreted and systematized by our intellects. The name itself is the plural of the word `physic,' which was used as early as fourteenth brteenth century to mean natural phi lusophy, but which afterwards became restricted to ine»n the science of medicine, and finally mean a medicine or drug itself. While phys?cs, in its modern sense collies closely in contact with chemistry, astronomy, and many other sciences, it is impossible to state in words its exact scope. it may be said, however, in general that the study of physics includes the phenomena of acousties, of heat, of light, of electricity and nuignetisin, and of mechanics to a certain extent. Within recent years many subdivisions have been made both in physics as a general study and also in its various parts. The subjects pertain ing to the nature of solutions are now included in physical chemistry; the spectroscopic examina tion of the sun, stars, etc., together with the re lated theories, forms the science of astrophysics; the observations and theories of earthquakes, heat conduction on a large scale, volcanoes, etc., are now studied under the mune of geological physics. Practical applications hare been made of Many observations in physics, and there are schools of engineering devoted to the study of these matters. Among the branches of engineer ing are mechanical, hydraulic, steam, and elec trical.
The fundamental idea of physics is that we learn by means of our senses certain facts in regard to natural phenomena, which are inde pendent of time and space. These last two con
cepts. namely those of time and space, are con sidered as intuitive. The name matter is given provisionally to whatever is the cause of our but it is defined, naturally, in terms of its properties. There is not necessarily in volved any assumption as to the reality of mat ter; rather, there are found certain mathematical expressions, certain differential equations, which express our knowledge of nature. but which we interpret in such language and with such ideas as correspond to our mental pictures. Asso elated with this idea there are two great di visions of physical methods; one may be called the laboratory method, the other the method of mathematical physics. (See 1...kaoaA.ToaY.) The laboratory method consists, first, in making a series of observations and amassing information in regard to phenomena, but further in seeking to obtain a generalization with which the ob served phenomena may be in accord. The object and scope of mathematieal physics ox pressr by Professor Poincar6 in his introduction to the Reports of the Int, rnational Congress of Physics (Paris, 1900). The fundamental method is to devise certain postulates and to state such axioms as will lead by rigid mathematical proc esses to which may be compared with observed phenomena. Thus by means of the methods of logic conclusions may he drawn con necting many phenomena which on their face are unrelated.