452 Miiasic. 



t>' 



just mentioned, the image of a hill, a tent, or of a liouse with 

 a steep roof, appeared at the first glance distinctly reversed ; 

 but if the hill had a white building on its summit, it might 

 always be seen that, if it appeared in the image, it was towards 

 the base, not at the summit, of the hill ; so, if the house had 

 white walls and a roof of red tiles, in the image the roof and 

 walls seemed to have changed places. 



But the hypothesis of a reflecting surface at the place where 

 the rarefied stratum and the dense one over it meet, will by no 

 means account for, it is even contradicted by, other observed 

 facts. On such a supposition, to see the image the eye must 

 be raised into the dense stratum above the supposed mirror, 

 and to make it disappear, the eye would only have to be lowered 

 into the rare stratum below it. But the facts are, that, as the 

 eye is raised, the mirage gradually disappears, and as it is 

 lowered it gradually increases, till at last, when brought close 

 to the ground, all is mirage, even the soil within a few feet not 

 being distinguishable. This I have often tried. Belzoni says 

 {Narrative^ p, 196.), " If the traveller stand elevated much 

 above the mirage, the apparent water seems less united and 

 less deep ; for, as the eyes look down upon it, there is not 

 thickness enough in the vapour on the surface of the ground 

 to conceal the earth from the sight. [This is Belzoni's theory, 

 but I quote him solely for his facts.] But if the traveller be 

 on a level with the horizon of the mirage, he cannot see 

 through it, so that it appears to him clear water. By putting 

 my head first to the ground, and then mounting a camel, the 

 height of which might have been about 10 ft. at the most, I 

 found a great difference in the appearance of the mirage." 



In stating the result of my own experience, I do not mean 

 to deny that other observers may have seen reversed images * ; 

 but / have never seen them, and therefore I have come to the 

 conclusion that they are not characteristic of this kind of 

 mirage. I am also of opinion that hasty observers, misled by 

 the extraordinary resemblance of the whole to objects reflected 

 from water, have often taken it for granted that the indistinct 

 images were reversed, when, in reality, they may have been 

 erect ; and that, in consequence, much perplexity has arisen, 

 and the idea of a reflecting surface has been had recourse to, to 

 account for this, perhaps imaginary, part of the phenomenon. 



* This communication has no reference to those cases of unusual 

 refraction where images are seen in various positions, erect, reversed, and 

 multiplied. Sir D. Brewster mentions that Dr. Wollaston, in looking 

 through a square glass bottle, containing water floating above syrup, saw 

 an object in its proper position, and under it an inverted image, but whether 

 by reflection or refraction, he does not say. This experiment seems to 

 have some relation to mirage, and to make against my theory. 



