478 Lieut-General Strarhey and Mr. Whipple. 



A.B before stated, the velocity in miles per hour is 



v _ ft 3600 

 ~ p ' 6280 ' ~7'~ 



To obtain the value of V graphically, proceed as follows : 

 Draw a horizontal line on which will be represented equal time- 

 intervals from to 120 seconds, see fig. 3. Erect vertical lines at all 

 the points between 60 and 120 seconds, which will include all the 

 time intervals between the pictures likely to occur in practice. On 

 the first of these verticals mark off any convenient length to represent 



