not easy owing to her aversion to such visits.

Turning to the domain of mathematical and physical science and of
scientific research and discovery, we find that here also the 17th
century Netherlanders attained the highest distinction. As
mathematicians Simon Stevin, the friend and instructor of Maurice of
Orange, and Francis van Schooten, the Leyden Professor, who numbered
among his pupils Christian Huyghens and John de Witt, did much excellent
work in the earlier years of the century. The published writings of De
Witt on "the properties of curves" and on "the theory of probabilities"
show that the greatest of Dutch statesmen might have become famous as a
mathematician had the cares of administration permitted him to pursue
the abstract studies that he loved. Of the scientific achievements of
Christian Huyghens (1629-95), the brilliant son of a brilliant father,
it is difficult to speak in adequate terms. There is scarcely any name
in the annals of science that stands higher than his. His abilities, as
a pure mathematician, place him in the front rank among mathematicians
of all time; and yet the services that he rendered to mathematical
science were surpassed by his extraordinary capacity for the combination
of theory with practice. His powers of invention, of broad
generalisation, of originality of thought were almost unbounded. Among
the mathematical problems with which he dealt successfully were the
theory of numbers, the squaring of the circle and the calculation of
chances. To him we owe the conception of the law of the conservation of
energy, of the motion of the centre of gravity, and of the undulatory
theory of light. He expounded the laws of the motion of the pendulum,
increased the power of the telescope, invented the micrometer,
discovered the rings and satellites of Saturn, constructed the first
pendulum clock, and a machine, called the gunpowder machine, in
principle the precursor of the steam engine. For sheer brain power and
inventive genius Christian Huyghens was a giant. He spent the later
years of his life in Paris, where he was one of the founders and
original members of the _Academie des Sciences_. Two other names of
scientists, who gained a European reputation for original research and
permanent additions to knowledge, must be mentioned; those of Antoni van
Leeuwenhoek (1632-1723), and of Jan Swammerdam (1637-80). Leeuwenhoek
was a life-long observer of minute life. The microscope (the invention