d 1-55,000 of an inch in length, as
Helmholtz has suggested, or, as seems to the writer more probable, the
substance purpurine is a highly complex organic substance made up of
molecules of different sizes and requiring wave lengths of different
orders to decompose them, so that a part of the substance may be quite
disintegrated, while other molecules may be quite entire throughout the
visual space. This will account for most of the chromatic effects of
vision, for complementary colors, and for color blindness, by supposing
that the purpurine is not normally constituted. This is in accordance
with experimental photography, for it has been found that the long waves
will act only upon heavier molecules. It is true vision may be good when
there is no purpurine, but there is no doubt but that this substance is
secreted in the eye, and that it is photographic in its properties, and
so far must be taken as an element in any theory of vision; but the
chief point here considered is that objectively light does not exist
independent of the eye, that light is a physiological phenomenon, and to
speak of it otherwise is to confound a cause with an effect. It is,
hence, incorrect to speak of the velocity of light; it has no velocity.
It is _radiant energy_ that has the velocity of 186,000 miles a second.
It is incorrect to say we receive heat from the sun. What we do receive
is radiant energy, which is here transformed into heat. This is not
hypercritical, but is in accordance with the knowledge we have to-day.
The old nomenclature we use, but without definite meaning; the latter is
left to be inferred from the connection or context. If a man should
attach to the water main in a city a properly constructed waterwheel,
the latter will rotate; but it would not be proper to say that he
received rotation from the reservoir. What he received was water with a
certain pressure; in other words, a certain form of energy, which he
transforms into rotation by the appropriate means; but by substituting
other means he can make the same water pressure maintain a vibratory
motion, as with the hydraulic ram valve, or let it waste itself by open
flow, in which case it becomes ultimately molecular vibration that is
heat. The analogy holds strictly. The trouble all comes from neglecting
to distinguish between different forms of energy--energy in matter and
energy in the ether.

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GLASS SPINNING AND WEAVING.