St. Nicholas/Volume 40/Number 5/Nature and Science/Know
Ice disappears from shore
Dear St. Nicholas: Will you please tell me, when a lake is frozen, why does the ice go out near the shore more quickly than out in the middle?
I think that the chief cause why ice melts more quickly about the edge of a pond than the rest of it, is that the surrounding earth is warmer than the water farther out. This is due largely to the fact that the darker-colored earth absorbs the sun’s heat much more than ice. This effect is seen when gravel is on the ice and exposed to sunshine. The stones are heated so much that they melt holes down into the ice.
That shallow water would warm up more quickly than deeper water is undoubtedly true, especially after the ice has gone at the edge, for the ice certainly reflects the sun’s heat more than the water does, so that the ice would tend to keep on melting around the edge of the pond.
Why hair turns white
Dear St. Nicholas: Why does a person’s hair grow white with age?
Your interested reader,
Helen Tallout.
The color of the hair is due to iron. which is picked up by the cells of the hair follicle in the little factory in the skin where hairs are made. As one gets older, the little cells which work at manufacturing hairs grow weary, and they will not take up as much iron as they once did.—Robert T. Morris.
Photographing a thunder-storm
No. 1 is a picture of an approaching storm taken with a color screen.
No. 2 was taken at night, during a thunder-storm. It was exposed about five minutes.
No. 3 was taken immediately after No. 2, and was exposed about eight or ten minutes. I would like to ask why some streaks are black and some white.
No. 4 was taken at night, when there was mach flash lightning but few streaks. It was exposed fifteen or twenty
No. 1. The approaching thunder-storm.
All these pictures were taken with a No. 3a folding Brownie camera.
Your interested reader,
Karl K. Nelson.
No. 2. The “ribbon flashes” of lightning.
In photograph No. 2, if the camera was stationary while the exposures were made, the two flashes which show double and treble are what are commonly called “ribbon flashes.” This ribbon effect can probably be accounted for in this way: we know that most flashes are multiple. By moving the camera, this fact is shown. It is possible that the wind, if strong, may push, and so shift somewhat, the path left by the first discharge, and, when other discharges occur, they will follow this path and so seem to be at a little distance from the place at which the first discharge took place.
No. 3. “A mass of streaks, some of them appearing black.”
No. 3 shows a mass of streaks, some of them appearing black. In this instance, I am positive that we have a plain case of “reversal,” that is, when a bright object appears as dark on the negative. We can cause reversal of the image in several ways, for example by photographing a spark from a static electric machine, and after it has been impressed on the plate, opening the shutter for an instant in a subdued light. We will then find, on developing, that the image of the spark has been reversed and shows black. In the case of this picture, the flashes which show black were the first which took place, and would have shown white if subsequent flashes had not appeared, or if the shutter had been closed before they came. As it was, these after-flashes acted like the after-light men- tioned as causing the reversal of the image of the spark from a machine.
No. 4. An example of puzzling results sometimes obtained.
No. 4 is a puzzle. It appears to have been caused by accidental light which entered the camera; but I should not like to give any positive opinion on the matter. I am in possession of a picture of lightning taken by myself which shows almost like the curved streak on this picture, and almost as broad. It is not in the foreground as this is, but in the sky, as are other flashes.—Alex Larsen.
Mr. Larsen has had extensive experience in photographing lightning by a variety of methods. The average observer would say that No. 4 represented merely some accident to the plate, as our critic first suggests.—E. F. B.