Page:The Harvard Classics Vol. 51; Lectures.djvu/104

 94 compound microscope, greatly increasing the powers of the eye; finally, that indefinable modernizing of the human mind wrought by the whole Renaissance, which made sound thought once more possible, and for the first time produced in Galileo a man worthy to stand beside Archimedes.

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." 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," 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