ACOUSTICS AND GRAVITATION. 



99 



of the thread of water within; for it will be seen that the meniscus under a' 

 is at a pressure excess of hpg as compared with the meniscus under a. If L 

 is the total length of the thread of liquid in the tube, we may define the co- 

 efficient (K) of diffusion (by volume) by the equation 



v=KOt(hpg)/L 



where v is the volume diffusing at nearly constant mean pressure in the time 

 t through an area a, the density of liquid being p = i . Hence 



v L _ i dh L 

 at hpg 2 dt hpg 



where dh/dt is the loss of head per second. The factor ^4 appears, since the 

 volume lost at a' appears at a, and their sum is equivalent to the loss of head. 

 The amount of diffusion is so small that corrections may be disregarded. 



116 



V 



-a 



w 



H7n 



10' 



,42 



i 1 i 



WjtylO ZO 30c%9 ty 



The observations made before the spring of 1914 were not satisfactory be- 

 cause of deficiencies of method. They were, therefore, discarded. Measure- 

 ment was thereafter made with the cathetometer. The following table gives 

 the essential data for the interval of 6 years 9 months and 6 days, with the 

 increment from leap years : 

 No. L, Diam. inside. Area. Date. tXio* 



10 



/ 20.0 cm. 

 // 15.7 



0.55 cm. 

 0.82 



0.24 cm. 1 . 

 0-53 



/I9I4-3-20 



\I920-I2-26 



dh 

 dt 



1.07 

 1-73 



I. 10 



1.87 



The two values of K found are of the same order, but the one for tube 

 // is definitely larger than the one for tube /. This may be due to infin- 

 itesimal difference in the separated gases (a, a') of the tubes. Since the 

 tube // has a shorter (L) and wider column, and a meniscus nearer the bend, 

 it is more probable that thermal correction is the cause of the difference, for 

 the inside sectional area of // is about 2.2 times larger than /. The data ob- 

 tained for K with a cylindrical Cartesian diver * about 3 cm. in diameter, 



"Carnegie Inst. Wash. Pub. 186, p. 21, 1913. 



