Six Lectures on Light

Six Lectures on Light
Delivered In The United States In 1872-1873

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5
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Six Lectures on Light by John Tyndall

Published:

1906

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Six Lectures on Light
Delivered In The United States In 1872-1873

By

5
(1 Review)

Book Excerpt

this star. Instead of being produced by ten cells, it is produced by fifty. Placed in a suitable camera, provided with a suitable lens, this powerful source will give us all the light necessary for our experiments.

And here, in passing, I am reminded of the common delusion that the works of Nature, the human eye included, are theoretically perfect. The eye has grown for ages towards perfection; but ages of perfecting may be still before it. Looking at the dazzling light from our large battery, I see a luminous globe, but entirely fail to see the shape of the coke-points whence the light issues. The cause may be thus made clear: On the screen before you is projected an image of the carbon points, the whole of the glass lens in front of the camera being employed to form the image. It is not sharp, but surrounded by a halo which nearly obliterates the carbons. This arises from an imperfection of the glass lens, called its _spherical aberration_, which is due to the fact that the circumferent

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