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frequent oscillations. The same phenomena can be 

 produced by the passage of an electric current through 

 rarefied gases, the different colors shown arising from 

 the passage of electricity through the various gases. 

 An excellent illustration of this is shown in the geissler 

 tubes. 



The milk-maid's path is also observable, generally 

 reaching across the sky in an arched manner, but has 

 no definite edges, gradually blending out of sight in 

 the blue of the surrounding sky. It is white and not 

 very broad, and may often be seen on clear evenings, 

 but is not so attractive as the preceding subjects. 



St. Elmo's Fire is among the remainder of these 

 sights and objects. When the atmosphere is highly 

 charaed with electricity, faint tongues of fire are often 

 seen on objects in connection with the earth, such as 

 the masts of ships, spires and steeples. They are harm- 

 less, and are mostly observed in times of thunder show- 

 ers and storms. 



The Mirage is another curious occurrance which is 

 sometimes seen in deserts over the hot aired sand when 

 the strata of air rapidly increases from the surface up- 

 wards. The rays of light from distant objects are re- 

 flected from one of the lower layers of air, and, enter- 

 ing the eye of the observer, appears to come from in- 

 verted objects, looking as if they were surrounded by 

 a sheet of water. The mirage frequently occur at sea, 

 and vessels which are too far below the horizon to be 

 discernable are seen inverted by refraction. This phe- 

 nomena is called loaming. The vessels are seen both 

 erect and inverted, and sometimes appear as if suspend- 

 ed in the clouds, and distant islands are occasionally 



