■v^^LLsox. — altitude of aeropl.\ne flights. 



41 



referred ; for example, rate of ascent per minute, gradient with and 

 against the wind, etc. The reader who wishes to study them more 

 minutely may tlierefore msh to plot them on a scale suiHciently large 

 for his purpose. To make use of the sextant as well as the transit 

 observations in plotting the spirals, it is necessary to know the relative 

 position of the two bases. The north end of the field base is distant 

 15,000 feet and 14,700 feet from Q and 'Si respectively. The south 

 end of the field base is 10,050 feet from Q and 11,005 feet from M. 



In regard to these tables we notice that there is apparently a small 

 systematic ditierence between heights as observed at Q and M. This 

 was at first suspected to be due to error in level of the two stations, but 

 was not the same at all times. It was not due to difference in time ot 

 observation at the two stations, for although the setting at Milton was 

 always a fraction of a second later, this could only give rise to a differ- 

 ence of about one foot at most. It may have been partly due to 

 difference in levelling of instruments, and perhaps partly to neglect of 

 refraction and curvature of the earth in the computation. 



asort 



3000 



2.J00 



80OO 



I50f) 



1000 



500 



a b 



FiarRE 0. Time-altitude curve. (Left) flight of Johnstone, September 7 

 (Wright hii)iane); (right) flight of Gruhame-Whitc (Bld-riot monoplane), and 

 fligiit of Brookins (Wright biplane). 



The time-altitude curves have been plotted for all the flights of the 

 meet which have any special interest. Those of Brookins, Johnstone, 

 and Grahame-White on September 7 are i)lotted in Figure (>. They 

 show the typical rate of ascent of the Wright biplane, about 100 feet 

 per minute, in direct comparison with the BK'riot which was in the air 

 at the same time and rising mure than 200 feet per minute. 



