FLO WAGE IN SUPERCAPILLARY OPENINGS. 137 



seen, this is a matter of controlling consequence in flowage in small and 

 especially in very small openings. 



supercapiiiary openings — The flowage of water through supercapillary tubes 

 is controlled by the ordinary laws of hydrokinetics. Ignoring friction, 

 the flowage of water is as the square root of the pressure or head. If 

 V— velocity, H— head, and Gr— force of gravity, then V per second 

 =V2GrH. For instance, the velocity resulting from a pressure of 1 atmos- 

 phere or a head of 1033.3 cm. would be the square root of 2 X 981 X 

 1033.3 — 1423.8 cm. per second." 



This formula is only approximately correct, for the internal friction in 

 supercapillary tubes is dependent upon the viscosity of the solutions, upon 

 the regularity of the openings, upon their length and size, and upon the 

 velocity of flowage. If the openings be not straight, or vary in size, or 

 both, eddies form, which increase the internal friction and decrease the 

 speed of movement. The friction between the moving liquid and that fixed 

 to the walls increases with increase of length, with decrease of size, with 

 roughness of surface, and with increase in velocity. If the available area 

 be great and the movement consequently very slow, the resistance per unit 

 of length due to friction becomes so small as to be almost inappreciable. 

 But even if the openings be large and continuous the formula gives some- 

 what too high results. If the flow be rapid in long, rough, irregular 

 underground passages, the resistance is so great as to make the formula 

 above given inapplicable. 



Supercapillary openings include the greater number of bedding part- 

 ings, fault openings, joint openings, some of the openings of fissility, and 

 the openings in the coarser mechanical sediments, such as coarse sandstones 

 and conglomerates. The distance from an angle to the opposite side of the 

 roughly triangular tubes (fig. 3, p. 132) in sandstones composed of spherical 

 grains of equal size, which average 3 mm. in diameter, somewhat exceeds 

 0.508 mm. 6 The average diameter of the pores in the system of closest 

 packing is 43' per cent greater than the minimum section of the triangular 

 pores." It therefore follows that a sediment composed of grains just large 



«Daniell, Alfred, A text-book of the principles of physics, 3d ed., Macmillan Co., New York, 1895, 

 p. 303. 



&Slichter, C. S., Theoretical investigation of the motion of ground water: Nineteenth Ann. 

 Rept. U. S. Geol. Survey, pt. 2, 1899, p. 316. 



«Slichter, cit., p. 317. 



