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built, consisting of arch spans and piers, or steel to float an ocean steamship of large size, and bridges resting on concrete piers, some spans of where the locality is exposed directly to the gales the latter being two hundred and forty feet. This from the Atlantic, much of the work has been was the most difficult part of the work. The wa- performed with floats, on which the concrete was ter is from ten to thirty feet deep, and the bottom mixed and from which it was placed in position is coralline rock. There are twenty-eight of by means of powerful derricks. In the shallower these arch viaducts, aggregating ten and eight waters molds for the foundation of the viaduct tenths miles in length, and eight steel bridges, were formed by driving piling which held in aggregating six and one tenth miles in length. place a water-tight framework, which, when the

The longest viaduct is between Knight's Key water was pumped out, was filled with concrete. and Little Duck Key, seven miles, and is called This, the only railway of the kind in the world, the Knight's Key Viaduct. In many places the is now in actual operation, and reflects great embankment for the roadway is eight or nine credit on modern enterprise and skill. Both land feet in height, the road-bed being ballasted with and sea are laid under tribute; and these islands, coralline limestone, of which these islands are which have been likened to lazy lizards sleeping composed. This makes a very strong, safe road. through uncounted centuries, now teem with life

In many places where the water is deep enough and thrill with the rush of commerce.

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93. ????????????

new york

main at the same height, the horizontal bars “BECAUSE WE

remain in the same relation to the eyes and to

Ist. Nicholas WANT TO KNOW"

the object on the other side, and make a strong Union Square, impression on the retina. As they are darker

than the background, they produce a sharp afterimage when the eyes are turned away. There

seem to be several horizontal lines in the afterPUZZLING IMPRESSIONS ON THE EYES FOREST GATE, LONDON, ENGLAND.

image because you probably look for a while at DEAR ST. NICHOLAS: When I walk rapidly by vertical the upper part of that object on the other side, railings, and, as I walk, look at some object on the other then for a while at the middle part, then for a side of these railings, all is clear. But when I turn away while at the lower part. With every raising or

lowering of the eyes, the image of the horizontal bars falls on another spot in the retina, and leaves there the condition for another after-image, producing in this way a series of parallel horizontal lines.-H. M.

Note: A scientific friend says he ha observed that when an automobile passes under a light at night, the wheels seem to him to run back

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ward.

THE FENCE WITH UPRIGHT AND HORIZONTAL BARS.

tell me.

WHEN SPRING “PEEPERS" ARE HEARD

PURCHASE, X. Y. DEAR ST. NICHOLAS: Can you tell me why peepers do

not peep in the morning? If you can, I wish you would for a few seconds, there appear lines running before my

Your interested reader, eyes. What I want to know is, why are these lines hori.

BENJ. COLLINS, JR. (age 10). zontal, and why do they move horizontally, instead of being vertical lines moving horizontally, as you would expect Frog "peepers" are nocturnal animals, and selfrom an image that remains in your eye? Yours, puzzle,

dom active except during the late afternoon or

R. T. CLAPP. at night. I have heard them calling during the What happens is, that the upright bars of the day, but they usually begin to evince signs of inrailing make no lasting impression on your eye.

terest in things as the day comes to a close, and As you look at the object on the other side of the

continue the calls during the night. — RAYMOND L. DITMARS.

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WHY BRUISES BECOME “BLACK AND BLUE"

New YORK Muls, N. Y. DEAR ST. NICHOLAS: I have often wondered what makes black-and-blue marks on your skin when you are bruised. I take physiology and am very much interested in it, but my book fails to answer this question. I should be very much obliged if you would tell the reason.

Yours as ever,

Lois W. KELLOGG (age 13). The color of blood is due chiefly to iron in the little blood-cells. When the iron is kept in these little blood-cells, which are living and traveling around in the blood-vessels, the color is red. Hit the skin hard enough to break some of the little

blood-vessels beneath the surface, and the little THE IMPRESSION ON THE EYES WAS OF HORIZONTAL red cells escape from the injured blood-vessels,

BARS (UPPER PART OF THIS ILLUSTRATION) AND NOT wander about for a while in the tissues, and die.
VERTICAL (AS IN THE LOWER PART), AS ONE WOULD
SCPPOSE.

When they die, the iron that made them red be

fore, then changes to black-and-blue coloring. fence while you are walking along, the vertical After a while, this iron is taken up by the glands rods quickly pass in front of your eye and there called the lymphatics, and made over again into leave no after-image.

nice red cells. The iron is taken up very much But the image of the horisontal bars always more quickly by the lymphatics if the black-andfalls on the same spot in the retina at the back blue spot is rubbed and massaged. - DR. ROBERT of your eye, and as, in walking, your eyes re- T. MORRIS.

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FRAGRANT FIREWORKS

FIREWORKS FROM FLOWERS WORCESTER, Mass. Dear St. Nicholas: Orange-peel fireworks are great leaves and bears curious flowers, "gives off dur

The gas-plant (Dictamnus), which has fragrant fun. Papa and my brother Roland squeeze the rinds and I hold the match. Sometimes when the orange peel is ing hot weather a fragrant, volatile oil, which

ignites when a match is applied to it."

Mr. Nathan R. Graves, Rochester, New York, sends the accompanying illustration of the bloom. He writes:

"I have found that the flash, when a lighted match is held near to the bloom, is more certain on a sultry evening after a very warm day. Then one seldom fails to get quite spectacular results."

The gas-plant is attractive and of value aside from its peculiar inflammable gas. The seeds should be sown in the autumn in a plant nursery bed where they are to remain for two years.

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PRODUCING A FLASH BY IGNITING THE VOLATILE OIL

FROM ORANGE PEEL.

fresh and full of oil, a great fountain of flame flashes more than a foot high. Squeezing the rind and at the same time giving a quick pinch, cause the greatest outburst of oil and so the largest flash.

The orange-oil as it is thus burned perfumes the room like incense. We never tire of fragrant fireworks. Very sincerely yours,

MAZIE E. HODGE. These interesting fireworks were exhibited to me by the son and daughter of Professor Clifton F. Hodge when I was a guest in his house. Sev

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HOW TO HOLD THE LIGHTED MATCH, HOW TO MAKE
A SHARP BEND IN THE FOLDED PEEL, HOW TO
FOLD THE QUARTER PEEL, AND HOW TO PEEL THE

THE BLOOM OF THE GAS-PLANT, OR “BURNING BUSH. ORANGE.

(Dictamnus fraxinella.)

In dry, sultry weather the flowers sometimes give out a vapor which eral demonstrations of•the method were made. I is inflammable. took the accompanying photograph, and later an- They can then be transplanted to rich, heavy other to show how the peel should be held. This soil. They bloom in the months of June and July. experiment, like all in which a flame is used, how- [The fireworks with orange peel and flowers ever, should only be tried under the supervision have in themselves no danger, but, because of an older person, and care should be taken to matches are so common, one should never grow keep at a safe distance from any inflammable careless in the use of them, even to light a materials. – EDITOR OF “NATURE AND SCIENCE.” lamp.-E. F. B.]

Vol. XXXIX. – 107.

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