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ally let in more and more light, and the deep-red cloth will change to a lighter and lighter shade, till the room is fully lighted, when it will appear in its real color. Bring the red cloth into the full sunlight, or throw a beam from the heliostat

upon it, and it assumes a still lighter shade of red. Close the shutters again, and it will change back from red to dark-red, and through every shade to perfect black. Try any other color in the same manner, and you will produce precisely the same effects. This experiment may be tried in the night by turning the gas (or other lamp) slowly down till the light disappears, and turning it up again, while you watch the changing shades of color as the light decreases and increases.

Here we have quite a different matter, showing that the shade or brightness of a color depends upon the amount of light it receives. If it has plenty of light, it appears of its normal shade; if it has less light, it takes a darker shade; if more, it has a brighter shade. If, in using our color-top, we put a bit of black cloth or paper on the colors, the ring of color, when the top spins, will take a darker shade. If we put on a piece of white paper, we shall get rings of a lighter shade.

When the sunlight falls on any object, the object absorbs part of the light and reflects the rest. If it absorbs all the light and reflects nothing, the eye sees no reflected rays, and we say the object is black, or is invisible. If it reflects all the light, all colors enter the eye, and we say it is white. If it absorbs all the rays of the spectrum except red, our eyes receive these red-reflected rays, and we call the object red. If it absorbs all the rays except red and green, the eye receives these two rays, two sets of nerves are excited at once, and we say that the object is yellow. It is in this manner that we see the things about us, and are enabled to recognize the colors in which they appear to be clothed.

CONCLUSION.

We have now seen how light moves through air, water, and other transparent substances; we have learned something of the manner in which it may be reflected and refracted ; and we have examined a few of the more simple facts about colors. Yet we have not by any means learned all that is known about light, nor have we exhausted half the capabilities of our apparatus. We have studied reflection from plane surfaces : all the wonderful effects produced by reflection from curved mirrors remain for further study. We have examined only one or two of the different kinds of lenses; and in the beautiful science of colors we have, as it were, only opened the gate into a strange and marvelous country.

You might go on for a year and still make experiments every day, and even then not reach the end. You have seen that it is not difficult to make experiments; and, should you take up other books on light and make new experiments, you would find much that would be of the greatest value and interest.

Should you learn nothing else, you will see for yourself with what skill, wisdom, and goodness, all these beneficent laws have been arranged. These things came not by chance, or of themselves. They all point to a great and wise Creator, who has given the light a pathway, and filled it with bewildering and perpetual beauty. It is the light that paints the flowers, tints the clouds, and decks the sky in blue. Everything selects its own particular color out of the solar spectrum, and shines with all the beauty and glory of the light. No man hath counted all the glories of light, nor hath any man yet traced all its paths. It brings us strange messages from distant suns; it makes all Nature beautiful.

Having made a fair start in the art of experimenting, let us go on to new experiments in sound, heat, magnetism, electricity, and mechanics.

THE END.

List of Apparatus used in the Experiments on Light,

with the prices, as supplied by Samuel Hawkridge, successor to George Wale & Co., Hoboken, New Jersey.

Heliostat

.$5 00 Water-lantern.

5 00 Glass tube.

05 Pulse-mirror..

05 Square bottle for refraction.

15 Plano-convex lens...

75 Small double-convex lens.....

50 Flask for condenser of solar microscope..

75 Glass cylinder for experiment of the illuminated jet-to be used

with plano-convex lens in place of the large flask shown in
Fig. 23...

1 50 Glass prism.

50 Top .....

10 Cake of vermilion paint.

15 Cake of emerald green paint.

15 Nuremberg violet, in powder, to be used with gum-water..

15 Two small slips of clear glass..

05

$14 85

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