HUNTERS AND MIRAGE. 207 



set of causes which comes into operation upon dry 

 plains subject to high solar temperatures, caused by 

 local peculiarities in the state of the atmosphere itself 

 to which we desire to call our readers' particular 

 attention. This is irrespective of the curious vagaries 

 of mirage, which causes everything to vibrate exactly 

 like the waves of hot air that may be seen rising 

 from a heated iron plate. It has all the effect of an 

 exhalation of gas from the surface of the ground, and 

 when it is present in any marked degree it so distorts 

 all natural objects in the landscape that it is impossible 

 to be sure of either what they are, or how far off 

 they are. Anything like accurate shooting therefore, 

 when there is much mirage, is out of the question. 



But there are other occasions, when the exceedingly 

 clear and transparent nature of the atmosphere (due in 

 a great degree to the abnormal absence, or rather the 

 dispersal of vapour through space) is so perfect as to 

 exhibit all objects in the distance as if they were much 

 nearer at hand than they really are: thus constituting 

 another optical illusion of the most remarkable kind. 

 This condition of the atmosphere may arise at any time 

 of the day, but it is most common (so far as our 

 humble judgment goes) in the early hours, because the 

 prospect is then generally uncomplicated by mirage, which 

 as a rule only prevails after the earth's surface has become 

 heated by the powerful rays of the midday sun. 



The larger the object, of course the greater will be 

 the deception; rocky hillocks or a bush-covered mound 

 will thus appear to be only a short distance ahead; 

 but in reality they are quite a considerable way off, 

 as the traveller soon discovers in moving towards 

 them. This illusion is however best seen in its most 



