The forms of water in clouds [and] rivers, ice [and] glaciers / by John Tyndall.

  • Tyndall, John, 1820-1893.
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: The forms of water in clouds [and] rivers, ice [and] glaciers / by John Tyndall. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    § 3. The Waves of Light. 20. But what is the sun ? We know its size and its weight. We also know that it is a globe of fire far hotter than any fire upon earth. But we now enter upon another enquiry. We have to learn definitely what is the meaning of solar light and solar heat; in what way they make themselves known to our senses ; by what means they get from the sun to the earth, and how, when there, they produce the clouds of our atmo- sphere, and thus originate our rivers and our glaciers. 21. If in a dark room you close your eyes and press the eyelid with your finger-nail, a circle of light will be seen opposite to the point pressed, while a sharp blow upon the eye produces the impression of a fiash of light. There is a nerve specially devoted to the purposes of vision which comes from the brain to the back of the eye, and there divides into fine filaments, which are woven together to a kind of screen called the retina. The retina can be excited in various ways so as to pro- duce the consciousness of light; it may, as we have seen, be excited by the rude mechanical action of a blow imparted to the eye. 22. There is no spontaneous ci-eation of light by the healthy eye. To excite vision the retina must be affected by something coming fi-om without. What is that something? In some way or other luminous