HISTORY OF PHYSICS. It is remarkable to note how few facts other than obvious ones were known to the ancients in regard to nature and also to find how few instrunients were available for wlmt may be called scientific observation Beyond a doubt simple forms of instruments were known for the measurement of time, such as water-eloeks, sun-dials, etc., and the Chinese at least had a knowledge of some of the simple properties of a magnet. The law of the reflection of light was generally known and lenses were in use for various purposes. The law of the lever was known to Archimedes, as were also certain of the laws of hydrostatics. There was a knowl edge of harmony in ninsie more or less incom plete. A few observations are also noted in regard to electric attraction and the facts of meteorology.
Up to the Middle Ages there are few if any facts to be recorded in regard to the growth of natural philosophy, because the 'Romans were content with the knowledge left them by the Greeks, and the intellectual activity of the Arabs seemed to be concentrated, as far as physics is concerted, in the person of Al-Hazen, who was interested largely in optics. There was a re vival of interest in nature during the thirteenth century, as shown by the work of Roger Bacon and Peregrinus. In the sixteenth century Coper nicus lived, and he was followed by Galileo, Kep ler, Stevie, Gilbert, and others.
The effect of the life and work of Galileo in Italy and of Gilbert in England cannot be over estimated. There was a universal revival of in tellectual activity and a universal interest in the study of natural phenomena. Each of these two men emphasized the need of experimental study and the futility of logic apart from observation. Galileo's greatest contribution to physics was the statement of the principles of mechanics. He was succeeded by pupils whose interest and influ ence was so great that they led to the establish ment of academies and learned societies through out Europe. With the appearance, however, of Huygens's Tforo/ogium Oseinatorium (1673) and Newton's Principia (16S7) physics came to the front as the most important of the sciences. The methods used by these two men, both in their observations and in their state ment of laws of nature, have served as the models for succeeding generations. They were followed by two schools, one interested in the mathematical development of nmehanies, the other interested in the purely experimental side of the subject. whose legitimate predecessors were Torrieelli, Pascal, Boyle, and Cuericke.