Light; a course of experimental optics, chiefly with the lantern . e nature is easily understood. We have (§ 61)supposed vision to be excited by motion communicatedtransversely to the ends of fine rods, with which the retiflais studded, and so communicated through the nerves to thebrain. Now, if we press a rather blunt pin-point on anypart of the body, or excite sensation in any other way, wefeel it at first very vividly; but by degrees the sensation VI.] COLOUR A SENSATION. 125 deadens, and we take no notice. The nerves which respondto that particular feeling are by exercise, for the time,fat
Light; a course of experimental optics, chiefly with the lantern . e nature is easily understood. We have (§ 61)supposed vision to be excited by motion communicatedtransversely to the ends of fine rods, with which the retiflais studded, and so communicated through the nerves to thebrain. Now, if we press a rather blunt pin-point on anypart of the body, or excite sensation in any other way, wefeel it at first very vividly; but by degrees the sensation VI.] COLOUR A SENSATION. 125 deadens, and we take no notice. The nerves which respondto that particular feeling are by exercise, for the time,fatigued—tired out—and can no longer do their is the reason we wear our clothes without feeling them,and of many similar facts. Now if we suppose some ofthe rods to respond, like tuning-forks, to certain vibrationsor colours, and other rods to others, we ought to expect,under similar circumstances, results of the same is our next step in the demonstration, and the objectof our next experiments. Two lanterns may be used, one ?_-S-=-jE=sJ5J.
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