98 



EXPERIMENTS IN AERODYNAMICS. 



velocities were used ranging from 7 to 30 meters per second (11 to 67 miles per 



hour). The mean of 10 observations with the 6-inch plane, at velocities between 



25 and 30 meters per second, gave k m = 0.0081 ; and the mean of 12 observations, 



at velocities between 7.1 and 14. '.\ meters per second, gave the same value. 



Therefore the departure from the law of the squares, if there be any between 



these limits of velocity, is not sufficiently large to be detected by this apparatus. 



If variations in the density of the air produced by changes of temperature 



be considered in their effect upon the relation between pressure and velocity, the 



preceding formula may be expressed in the form 



p _ A- m V 1 



1 + .00366 (t — 10°)' 



where .00366 is the coefficient of expansion of air per centigrade degree; t is the 



temperature of the air expressed in centigrade degrees, and k m is the value of 



the coefficient for a standard temperature of 10° C. In the following summary, 



all the values of k m are collected and reduced by aid of this formula to a common 



mean temperature of 10° C. ; the values refer, also, to a mean barometric pressure 



of 736 mm. An additional column is added, giving the corresponding value of 



k in English measures for velocities expressed in feet per second and pressures in 



pounds per square foot. 



TABLE XVIII. 

 Summary of values of k m obtained with the RoUing Carriage. 



