r 



o 



93 ATMOSPHERICAL PHENOMENA. 



hindj and soon rejoined the wagons. The 

 optical illusions occasioned by the rarified and 

 transparent atmosphere of these elevated 

 plains, are often truly remarkable, afFordii ^ 

 another exemphiication of its purity. One 

 would almost fancy himself looking through 

 a spy-glass, for objects frequently appear at 

 scarce one-fourth of their real distance — ^fre- 

 quently much magnified, and more especially 

 elevated. I have often seen flocks of ante- 

 lopes mistaken for droves of elks or wild hor- 

 ses, and when at a great distance, even for 

 horsemen ; whereby frequent alarms are oc- 

 casioned. I have also known tufts of grass 

 or weeds, or mere buffldo bones scattered on 

 the prairies, to stretch upward to the height of 

 several feet, so as to present the appearance 

 of so many human beings. Ravens in the 

 same way are not unfrequently taken for In- 

 dians, as well as for buffalo ; and a herd of 

 the latter upon a distant plain often appear 

 so increased in bulk that they would be mis- 

 taken by the inexperienced for a grove of 

 trees. This is usually attended with a con- 



and looming, which often so 

 ^\Trithe and distort distant objects as to rendei 

 them too indistinct to be discriminated. The' 

 illusion seems to be occasioned by gaseous 

 ors rising from the around while the 



beamuig rays of the sun are darting ^ 



But the most curious, and at the sarne time 

 tlie most perplexing phenomenon, occasioned 

 by optical deception, is the mirage, or, as fa- 

 miliarly called upon the Prairies, the ' false 



