To it all the rest is merely preliminary, and
in it the final move is made which commits us to the deed. About it,
therefore, we may well desire the completest information. To tell the
truth, I have none to give, and nobody else has. The nature of the
operation is substantially unknown. Though something which we have
been performing all day long, we and all our ancestors, no one of us
has succeeded in getting a good sight of what actually takes place.
Our purposes are prepared as I have described, and then those
purposes--something altogether mental--change on a sudden to material
motions. How is the transmutation accomplished? How do we pass from a
mental picture to a set of motions in the physical world? What is the
bridge connecting the two? The bridge is always down when we direct
our gaze upon it, though firm when any act would cross.
Nor can we trace our passage any more easily in the opposite
direction. When my eyes are turned on my watch, for example, the
vibrations of light striking its face are reflected on the pupil of my
eye. There the little motions, previously existing only in the
surrounding ether, are communicated to my optic nerve. This vibrates
too, and by its motion excites the matter of my brain, and then--well,
I have a sensation of the white face of my watch.
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