**NEWTON’S “PRINCIPIA”**

In many respects the seventeenth century is the most interesting in the history of science, and certainly science is the most important human interest in the history of this century. Galileo begins it. “Modern science is the daughter of astronomy; it has come down from heaven to earth along the inclined plane of Galileo, for it is through Galileo that Newton and his successors are connected with Kepler.”〖Bergson, “Creative Evolution,” translated by Mitchell, p. 335.〗 The investigation of the falling body, and the establishment of the algebraical and geometrical laws of fall by Galileo, joined with Kepler’s great discoveries of the laws of planetary motion, and informed by the hypothesis of Copernicus, led to Newton’s “Principia,”〖H. C., xxxix, 150ff.〗 a work (the only other one by an Englishman) that stands out like that of Shakespeare, towering over all else.

This incomparable book contains all the essential principles of the science of mechanics. Since the year 1687, when it was published, the labor of many men of great genius has only availed to polish, to refine, and to embellish a subject which they could not really extend. In the course of the studies leading up to this work, Newton, incidentally as it were, invented the differential and integral calculus, which became the source not only of countless achievements in mathematics and science, but of perhaps the bitterest controversy in the annals of learning.

The work of Newton in establishing the science of mechanics was dependent upon a variety of other achievements of the century, in addition to the directly contributory labors of Kepler and Galileo. Especially important were the earlier progress of mathematics, marked by the invention of logarithms by Napier and independently by Bürgi, and the above mentioned discovery of analytical geometry by Descartes. Newton’s work was also dependent upon the growing power and precision of scientific instruments and measurements.

This development of mechanics from Galileo to Newton is perhaps the best illustration of the method of scientific progress. Upon a vast basis of accurate descriptive knowledge, erected partly by Tycho Brahe and partly by earlier astronomers, observations with instruments of precision and high power, quantitative experiments, and finally mathematical calculations produced in little more than half a century a work which it taxes the highest powers of the specially trained human mind to understand, and which has withstood all criticism for two centuries, the most critical in history.