e discovered a new property of matter--one of the secrets of
the Creator--and have calculated and discovered the effects of it. After
this, shall people quarrel with me about the name I give it?"

Vortices may be called an occult quality, because their existence was
never proved. Attraction, on the contrary, is a real thing, because its
effects are demonstrated, and the proportions of it are calculated. The
cause of this cause is among the _Arcana_ of the Almighty.

"Precedes huc, et non amplius."

(Thus far shalt thou go, and no farther.)

LETTER XVI.--ON SIR ISAAC NEWTON'S OPTICS

The philosophers of the last age found out a new universe; and a
circumstance which made its discovery more difficult was that no one had
so much as suspected its existence. The most sage and judicious were of
opinion that it was a frantic rashness to dare so much as to imagine that
it was possible to guess the laws by which the celestial bodies move and
the manner how light acts. Galileo, by his astronomical discoveries,
Kepler, by his calculation, Descartes (at least, in his dioptrics), and
Sir Isaac Newton, in all his works, severally saw the mechanism of the
springs of the world. The geometricians have subjected infinity to the
laws of calculation. The circulation of the blood in animals, and of the
sap in vegetables, have changed the face of Nature with regard to us. A
new kind of existence has been given to bodies in the air-pump. By the
assistance of telescopes bodies have been brought nearer to one another.
Finally, the several discoveries which Sir Isaac Newton has made on light
are equal to the boldest things which the curiosity of man could expect
after so many philosophical novelties.

Till Antonio de Dominis the rainbow was considered as an inexplicable
miracle. This philosopher guessed that it was a necessary effect of the
sun and rain. Descartes gained immortal fame by his mathematical
explication of this so natural a phenomenon. He calculated the
reflections and refractions of light in drops of rain. And his sagacity
on this occasion was at that time looked upon as next to divine.

But what would he have said had it been proved to him that he was
mistaken in the nature of light; that he had not the least reason to
maintain that it is a globular body? That it is false to assert that
this matter, spreading itself through the whole, waits only to be
projected forward by the sun, in order to be put in