[Barripore, January 5, 1844.]
MIRAGE AT POOREE.
There is one part of the sands at Pooree, on which if you stand about the middle of the day, and look towards the north, you are surprised to observe in the distance an English town. You see several three-storied houses, with doors and windows: interspersed here and there are several very English-looking trees; and at a short distance, standing on a small hill, you see the ruins of a large castle, with the green ivy clinging to it in many parts. Often have I stood and gazed upon this scene, for it reminds me of dear England. And yet, if you go to the place, what do you suppose you find? Nothing but one long flat bed of loose sand, without one vestige of a tree.
The appearance is caused solely by the refraction of the rays of light. To explain this I will give an example. If you hold a stick so that the lower part is in the water and the upper part in the air, the stick will appear to be bent at the point where it passes the surface of the water; or, place a shilling in a cup or basin, so that you cannot see it because the side of the cup hides it from you, fill the cup with water, and then you will see the shilling, although it is still in the same spot it was in before. This bending of the rays is what is called refraction, and is caused by the rays passing out of one transparent thing into another which is more or less dense than the first. I think that the cause of the mirage at Pooree is this. Hot air is less dense than cold air. The steam which comes from a kettle is still water, but it occupies a much larger space than the water did. One kettle of water will give much more than a kettlefull of steam, so that it is evident that the heat has made the water occupy a much larger quantity of space. Still the steam is only water; therefore it must be much less dense than cold water. If you filled a saucepan with water, and fastened the lid down, so that no steam could escape, it would burst it: the particles of heat cause the particles of water to be less closely connected together. But that is a subject too abstruse for this work.
Well, hot air, like hot water, is less dense than cold air; also water is more dense than air. You could not run along as quickly in the water as you could in the air; you could not strike a person with your hand under water hard enough to hurt him; and this is because the water is more dense or solid than air: therefore, air with a good deal of moisture in it is more dense than when dry. But along the hot sands of Pooree, close to the sea-shore, there must be a great deal of heat and also a great deal of moisture.
In the direction in which you look to see the mirage I mentioned, there is a small piece of stagnant water from which much moisture must arise under the burning heat of the sun; consequently there must be much refraction in all directions. And this is seen in looking the right way from all parts of the Pooree sands; and from the particular point to which I have alluded, this picture, owing, I suppose, to certain marks in the sand, assumes the appearance of a castle, houses, &c. All this is a very rough explanation; but it may serve to give you some idea of the probable cause of the mirage. Ships have sometimes appeared to be sailing in the air from the same cause; and distant coasts, which were far below the horizon, have been distinctly seen by means of the refraction.
[Guzzeepuddee, 8 miles from Balasore, January 12.]
SPORTING.