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100
attributed the invention of the magic lantern. The first telescope,
how-ever, was, according to one version of the story, constructed by a
Dutcli-man naraed Jansen, whose children while playing in their father’s
Morkshop accidentally placed a convex and concave spectacle glass at a
short distance from each other and noticed the apparent increase in
magnitude of what they saw through the glasses. They drew their
father’s attention to the phenomenon, and he fixed sucli glasses in a
tube and sold the instrument. It is certain that the principle of the
telescope was discovered in Holland, although it is not quite clear who
the discoverer was. But whoever he was, Galileo, having heard of the
instrument, made one himself, and with it discovered a satellite of
Jupiter. Great progress was now made in the study of light and colors.
Kepler, Porta, de Dominis, Snellius, Descartes, and Grihaldi both
en-larged the field of discovery and corrected previous results, preparing the
way for Newton, who in 1704 published his »Opticks», containing
experiments of the utmost importance and presenting his theory of light
and colors, which, although rejected as to its corpuscular philosophy, is
still accepted by the scientific world in many other respects.1
Newton’s theory briefly stated is as follows: Lights consists of
material particles or luminous corpuscles sent forth from a luminous body
in straight lines which by their mechanical action on the retina produce
sight. He says:2
»Are not the Rays of Light very Small Bodies emitted from Shining
Substances? For such Bodies will pass through uniform Mediums in
right Lines without bending into the Shadow, which is the nature of
the Rays of Light. They will also be capable of Several Properties and
be able to conserve their Properties in passing through several Mediums,
which is another Condition of the Rays of Light.»
Newton also attributes the heat of substances to the agitation of
their parts caused by the action of the rays.
Newton’s theory of light, according to the above quotation, is
there-fore an »emission» or »corpuscular» theory, its fundamental features
being similar to those combated ages before by Aristotle. Newton was
well aware of the »undulatory» theory, which considers light to be due
1 For a condensed history of theory and experiment on light and color see
Preston’s »Theory of Light,» Macmillan & Co., 1890, of which the present account is
for the most part an abridgement. For original documents see Goethe, Op. Cit., Vol. II.
* »Opticks», Bk. III., Qu. 29.
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