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PHYSICAL GEOGRAPHY. 



CHAPTER XVI. 



OPTICAL PHENOMENA. 



T is convenient to place an indefinite title at 

 the head of this chapter, in order to notice 

 various classes of independent phenomena 

 which immediately address themselves to 

 the eye ; and which are either plain develop- 

 ments of electrical action, or simply atmo- 

 spheric meteors, or appearances resulting from 

 its reflecting and refractive properties, or of 

 obscure origin, but manifested in the atmo- 

 sphere. To the former class the lightning 

 belongs, beautifully playing among the dis- 

 tant clouds, or flashing with blinding glare 

 and tremendous effect near the surface of the 

 earth, warning man and beast of the presence 

 of an agency able to extinguish animal and vegetable life in a moment, and utterly inap- 

 preciable in its swiftness, subtility, and power. At the close of a hot sultry day, over a level 

 country, the igneous meteor often exhibits itself, in rapidly succeeding, broad, noiseless, 

 and imposing sheets of flame, lighting up the whole range of the horizon, revealing for the 

 moment the contour of the distant landscape upon which the shadows of the night have 

 gathered, and discovering the outline of the clouds in the dusky sky. These displays, 

 however startling to " the poor Indian, whose untutored mind " is alarmed at the slightest 

 deviation from the ordinary aspect of things, are always harmless, and invite by their 

 innocuousness and fascination the cultivated races to watch the bounding coruscations 

 of the elastic element, besides contributing to render the fields of corn ripe unto the 

 harvest. But it is otherwise when heat has overcharged the atmosphere with vapours, 

 becoming piled into clouds of gigantic dimensions and massive architecture, which are 

 often propelled by antagonist currents, and in different electrical conditions. After an 

 unusual calm of nature, oppressive to the animal system, during which not a movement of 

 the air is perceptible, and the leaves hang motionless upon the trees, while the 

 brute creation indicate some intelligence of an impending change by their restlessness, 

 an explosion commences. The flash is seen, the thunder heard, and the clouds open their 

 watery storehouse, a few distant and heavy drops increasing into a cataract of rain. Flash 

 rapidly follows flash, and the interval between each appearance, and the accompanying 

 thunder peal becomes less. The pale hue of the lightning is exchanged for a vivid glare, 

 in which a deep yellow, red, or blue is the predominant colour, a variety of aberrations 

 marking its course, the zigzag form showing that the fearful agent is near terrestrial 

 objects. In this manner, "the destruction that wasteth at noonday" is frequently 

 exhibited, now striking man and beast to the earth, or rending asunder the mighty oak 

 of the forest, or firing the vessel of the hapless seaman, or shivering " the cloud-capt 

 towers and gorgeous palaces," the fanes of religion and the fortresses of war. Man has 

 then a solemn sense of his helplessness and danger ; and almost every creature sympathises 

 with him. The eel is restless in his muddy bed the horse trembles beneath his rider 



