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THE SEVENTEENTH CENTURY. 349
covered diffraction or inflection of light as well as its dis­
persion or splitting up into its constituent colours. The
last-mentioned, and HOOKE in even greater degree, when
he published his observations on the colours of thin films,
had suspicions of the undulatory movement of light which
HUYGENS, supported by the phenomenon of double refrac­
tion, raised by his undulatory theory into one of the facts of
science. It is true that it had to wait more than a century
before receiving general recognition; for NEWTON had
asserted that light consists of concrete particles which are
emitted from luminous bodies with great velocity, and his
authority w r as so powerful that all attempts which were at
variance with it were unavailing, for a time, to make truth
victorious. Not till 1815 did success crown the persevering
efforts of FRESNEL and ARAGO to secure a general accept­
ance for the undulatory theory.
The first contributions, also, upon the phenomena of
polarization — observed indeed by NEWTON but which
he was unable to explain intelligibly — date from the
end of the 17th century. On the other hand, in his
experiments upon the dispersion of sunlight, undertaken
by him after the method already adopted by GRIMALDI and,
before GRIMALDI, by the Prague doctor MARCUS MARCI of
Kronland, NEWTON arrived at the important result that
white light is composed of an infinite number of coloured
rays of different refrangibility and that to each degree of
refrangibility a particular colour corresponds. NEWTON'S
views upon the origin and essence of colours were not
correct; it appears that L. EULER in 1746 was the first who
had correct coherent notions on this subject. Many more
discoveries in physics belong to the 17th century,—dis­
coveries which have advanced civilization very greatly in
many directions. HOOKE improved the watch by inventing
the spiral spring, and HUYGENS was the first to construct a
pendulum-clock.
The Marquess of WORCESTER, Captain SAVERY, MORE-
LAND, PAPIN and others studied the power of steam very