ATMOSPHERIC FRICTION. 
265 
coefficient; also sin a = 1/ V 1 + # 2 , # being inches; and 
2/=0.0001263 # ~ 0 ’ 07 , the numerical equation becomes 
0 0130 
R = -r== + 0.0001263 # - 93 . 
V 1 + x 2 
The values obtained by substituting for x the various widths 
of the models are given in the table and shown by means of 
the curves in figure 7. 
The diagram portrays the main features of the equation 
very clearly. The total resistance falls rapidly at first, be¬ 
comes a minimum when the wedge is about one foot wide, 
then increases indefinitely with the width. The true head 
Fig. 7. —Computed and Observed Resistances of Symmetrical Wedges. 
resistance and the skin-friction, as shown by the lower 
curves, approach each other, becoming equal when the 
width of the wedge is a little below one foot, then diverge 
indefinitely, the friction being four times the true head 
resistance when the width of the wedge becomes two feet. 
We have thus found a formula which accords very well 
with the data of experiment; but its first term expresses only 
approximately the true head resistance and is here employed 
merely tentatively. In fact, the coefficient / had to be some¬ 
what increased to make the computed and observed values 
agree. Thus the term 0.000126# makes the skin-friction 
equal to 0.00127 of a pound, when#equals one foot, whereas 
by table IV it should be 0.00113. So probably the term c 
sin a gives values for the head resistance which are some- 
