The explanation will be the same as that of the diagram of the rising sun in a former page; if the ray from A took the direction D, as under ordinary circumstances it would do, it is evident that a spectator at C would see nothing. But instead of this, the ray was refracted near the middle to the point C, which represents the town of Hastings, and therefore the object A appeared as if it had been placed at B. You shall now hear what causes are likely to alter the refracting power of the air at times.

When air, water, or any other substance, is made hot, it becomes rarified, and its refracting power is thereby diminished. Have you ever watched, while you have been on one side of a stove, or of any heated body, the appearance of things on the other side through the air above it? If so, you must have seen how strangely they seem to tremble. Now this is caused by a stream of irregularly heated air rising from the stove, and enabling you every instant to see the things beyond it more nearly in their true position than you can through air of the ordinary temperature.

If you look through a magnifying glass at distant objects, they will appear upside down. You may learn why this takes place from books on optics. The same effect is produced by rays passing through a medium which becomes gradually denser, instead of suddenly passing from one state to another. Thus, if you take a square glass bottle and put some clear syrup into it, and then carefully pour water on the top of that, anything, such as a written or printed line, seen through the space where the liquids are mixing, will appear inverted.

Again, if you take a tin tube full of water, stopped with a piece of plain glass at each end, warm the middle of the tube, and then look at one end, you will see an object at the other end, if held at a proper distance, magnified, and distant objects turned upside down, just as they would be by a convex lens. If, on the contrary, you cool the middle of the tube, by applying ice to it, the same ensues as by using a concave lens. If a space of cold air be between two spaces of hot air, or the contrary, a space of hot air be between two spaces of cold air, the effects would be the same, only they could not be produced in so small a compass as they could with water. The space where the two different temperatures were gradually mixing, would influence the rays of light in the same manner as a lens on a very large scale.

Now portions of air are often made of different temperature by the sun's rays, by evaporation, as from the surface of the sea, or of lakes, or from marshy districts, and by winds operating under particular local circumstances. I do not want to lengthen out this dry story, but if you have read attentively what I have said, you will see that various positions of masses of air heated to different degrees, is all that is necessary to account for the instances which I have mentioned, in which objects have appeared inverted and out of their true positions; such as Dover Castle, Captain Scoresby's father's ship, the French coast opposite Hastings, and the islands, and horses with their legs upwards, described by Humboldt.

The apparitions of Souter Fell may be accounted for in like manner. The latter one was seen at a time of civil commotion, when there were private troops of horse exercised in all parts of the country, and so the fact of armed horsemen being in the neighbourhood, is rendered very probable. We have only to suppose the image of such a troop to be brought to the side of Souter Fell, perhaps from the opposite side of the mountain, by a complicated refraction, like that which appeared to move Dover Castle out of its place.

But the Spectre of the Brocken, the Fata Morgana, and the image which my friend saw of the side of the hill on which he was, require another sort of explanation, because the object and the image are seen both at once; the latter could therefore have been no other than the reflection of the first.

It seems likely that some vapours are capable of receiving shadows. When I have been bathing in a river with a muddy bottom, I have often seen my shadow on the cloud of muddy particles which I have disturbed from the bottom, in a manner something similar to that in which I should think this may occasionally take place.

There is, however, another theory of it. When rays pass from a thin medium into a denser medium, the whole do not go through, but they are strained, as it were, and a part are kept back and reflected. It is thus that you see a reflection on a transparent pane of glass.

If you breathe very lightly upon it, the reflection will be still more distinct, and the resemblance to the phenomenon we are describing probably greater. There are then two causes of reflection, the change of refracting power, and the presence of the watery particles.

Something of this kind perhaps occurs on the top of the Brocken. A rush of cold air may set up from deep ravines, with water and marshy land at the bottom, on the West side, while the rising sun is genially warming the air on the east side of the mountains. Mind, I do not say that it is so, but it does not seem unlikely that two currents, one of cold air and the other of hot, thus ascend close to each other; and according to what I have told you, there would be a reflecting power in the plane of contact, which might be increased by the watery particles carried upwards.

A kind of aerial screen would thus be formed, which might catch the shadow of a person on the opposite summit, cast upon it by the horizontal rays of the morning sun. Thus you may account for the image, and its being so greatly magnified, requires no further explanation than I have given above; as it only needs the supposition of a mass of heated air, with two colder ones on each side, being between the persons and the reflecting substance.

The doubling of one of the figures was possibly occasioned by a reflecting surface having been formed on a different plane from the first, which might very easily occur.