DISCUSSION OF MOTIONS OF METEORITES 



113 



near a plane lamina moving in a perfect liquid. The points D and 1)\ 

 where stream lines terminate on the surface of the meteorite, are points 

 of no motion, i) is a point of maximum pressure and D' is a point of 

 minimum pressure, for which reason the air is concentrated in a dense 

 mass in the neighborhood of /), while a partial vacuum surrounds D'. 

 The high pressure at D and the low pressure at D' evidently result in 

 an accelerating couple tending to turn the disc, in the case represented 

 in the diagram, in the direction of the hands of a watch. 



Figure 4. — Diagram showing Stream Lines about Discoid Body projected into the A erosphere. 



A B, direction of translation ; O, center of mass ; H, principal axis; 0, angle between principal 

 axis and path of meteorite ; C, center of pressure ; D D', points of no-air motion in reference to 

 disc. 



Rayleigh has shown that for a plane lamina moving in a perfect liquid, 

 the center of pressure — that is, the point at which a single force could 

 be applied which would exactly balance the total pressure exerted by 

 the liquid— is situated at a distance from the center of the lamina 



sin 



2 4 + TT cos 



in which 2/ is the width of the lamina and 6 is the angle between the 

 direction of motion and the normal to the lamina. The maximum 

 value of this expression is readily found to be 



-- 3 ; ] 



X max =— - 1 



o 



which means that the distance of the center of pressure from the middle 

 of the lamina cannot exceed an amount equal to three-eighths of the 

 semi-width of the lamina. This limit would be different for a discoidal 



XVI— Bull. Geol. Soc. Am., Vol. 14, TJ02 



