METEOROLOGY. 231 
certain time houses, palaces, colonnades, groves, hedges, &c., are seen 
above the sea, the whole being but the aerial reflection of the city of 
Messina and its environs. Most of the earlier descriptions of this wonder 
are exceedingly exaggerated and highflown. 
Monge, Vince, and Biot, have, more than any other philosophers, been 
occupied in investigating these interesting and remarkable phenomena. 
The latter has shown how, under certain circumstances, a line, bic 
( pl. 24, fig. 22), may be supposed drawn from a distant point, 6, beneath 
which ail objects will be invisible to an observer atc, while of all objects 
above this line two images will be seen, one direct above the line, and 
another inverted below. Thus a man walking from the observer would 
successively present the appearances of fig.22. 
Sometimes the unusual or secondary images lie neither above nor below 
the primary, but at one side of it. An apparition of this kind was seen by 
Soret and Jurine, Sept. 17, 1820, on the Lake of Geneva (pl. 24, fig. 23). 
While standing in the second story of a house on the bank, they looked 
through a telescope in the direction gp, at a ship, p, which was two miles 
off, and sailing towards Geneva. While the vessel came successively to 
cqrs, they noticed to the left hand distinct images, q’, 7’, s’, which separated 
more and more from the direct or primary image of the vessel with 
increasing approximation. The air over the lake on the eastern bank, 
ABC, at that time had been a good while in the shadow cast by the 
mountains of Savoy, while the left side was already heated by the sun. 
The plane of separation between the cold and warm air was thus vertical 
for a moderate height above the water. The sailing of the vessel just 
along the confines of the two regions produced the phenomenon in question 
On the Rainbow. 
Of all the optical phenomena of the atmosphere the rainbow is perhaps 
the most beautiful. It is seen when a spectator with his back to the sun 
looks in the opposite direction towards a shower of rain proceeding from 
an illuminated cloud. Two different bows are generally seen, one above 
the other, with their colors in the reverse order; the lower of the two is 
generally most brilliant. Suppose a straight line, OP (pl. 26, fig. 12), 
drawn through the sun and the eye of the observer, and a vertical plane 
passed through this line. Draw through O a line Oz, so that the angle POx 
amounts to 42°, then rain-drops which lie in the direction Oz will send 
colored rays to the eye, and as this is the case with all drops which lie in 
the surface of a cone formed by rotating the line Ox about OP, the eye 
will see a light circle of about 42° of radins. The centre of the circle lies 
where a line produced from the sun through the eye of the observer cuts 
the opposite sky, or where the shadow of the observer’s head would fall. 
The light of the sun entering the drops of water from above is refracted to 
the opposite internal surface, thence reflected to the lower part of the drop, 
and emerging reaches the eye of the observer, if he be at the proper 
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