THE DIMENSIONS OF TRAVEL 



reduction in the velocity of apparent ground flow, the bird has much more 

 time than the walking man for visual examination of any segment of the 

 landscape over which it travels. 



There remains the dimension of breadth. If the other three coordinates 

 have relative equality, the values of breadth are the same for man and bird. 

 But as the Canvasback rises above 82& feet it gains a great superiority in its 

 breadth of perception. Landscape patterns, such as lakes, rivers, and moun- 

 tains, beyond sight at lower elevations come into view, and errors in course 

 may be adjusted. The increase in the breadth of vision reduces the require- 

 ment of precision in aerial navigation. 



The four-dimensional comparison of man and Canvasback, then, may be 

 shown as follows : 



Travel Altitude Breadth 



Velocity Distance of Travel of Vision 



(M.P.H.) (Miles) (Feet) (Miles) 



Man 4 20 5.5 6 



Canvasback 60 300 82.5 24 



Man 4 20 133.3 30 



Canvasback 60 300 2,000 118 



It is only fair, of course, to note that all Canvasback travel does not take 

 place at 60 m.p.h. or at 2,000 feet, but we must apply the same four-dimen- 

 sional examination for any speed or altitude if comparisons are to be valid. 

 For example, if a head wind reduced the ground speed of the Canvasback 

 to 30 m.p.h., the comparison would be: 



Travel Altitude Breadth 



Velocity Distance of Travel of Vision 



(M.P.H.) (Miles) (Feet) (Miles) 



Man 4 40 266.6 42 



Canvasback 30 300 2,000 118 



Although only the velocity has been changed for the Canvasback, the 

 relative values of three other coordinates have thereby been altered for 

 man; 40 miles are now to man as 300 to Canvasback, but the elevation of 

 the eyes, in a fair comparison, is lifted to the 266.6 feet (as a man might 

 travel at 4 m.p.h. in a helicopter), and the breadth of vision must be in- 

 creased to 42 miles. 



• "The formula for the distance, d, at which an object h feet above sea level is visible to an 

 observer h' feet above sea level is approximately: d = 1.317 (v7» + V»') miles" (Griffiin, 

 1940:65). 



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