254 



Mr. K. Honda on a Portable 



The lead tubing I 



Fig. 2. 



Fig. 2 shows the recording apparatus, 

 is tightly connected to a glass 

 vessel B (3*5 cm. in diam.), 

 which is again connected, by 

 means of a thick caoutchouc 

 tube, to a glass tube G (1*8 cm. 

 in diam.). The two arms of the 

 U-shaped system are partially 

 filled with mercury, and the 

 pressure of the enclosed air is 

 balanced by the pressure due to 

 the difference in the heights 

 of the two mercury columns. 

 The change of pressure caused 

 by the change of the water- 

 level above the diving jar, 

 appears then as the motion of 

 the mercury column in the 

 tube C. 



To record the motion of the 

 meniscus, the following arrange- 

 ment * is used. A float made 

 of a -hollow ebonite box fits 

 loosely into the open arm of the 



tube. Upon this, a thin aluminium rod is vertically erected. 

 A pen-holder p, which carries two arms perpendicular to the 

 pen, is fixed horizontally on the upper end of the rod. At 

 the end of the arms, friction-wheels are attached which roll 

 in V-shaped grooves of two vertical guides gg. In this way, 

 the pen is constrained to move smoothly in a vertical line. 

 Though the pen is always pressed against the recording- 

 cylinder E by a weak spring, the friction is quite insensible. 

 The recording cylinder (20 cm. high and 9'4 cm. in diam.), 

 which contains the clock-work inside it, is vertically placed 

 just behind the two vertical guides and revolves once per day 

 about its fixed axis. The zigzags of the curves recorded on 

 the cylinder, which are due to the surface waves of short 

 periods, may conveniently be eliminated to a desired degree 

 by turning the cock k through a suitable angle. 



Fig. 3 is the photograph of the apparatus ready for setting ; 

 the reduction is one-sixth of the natural size. 



The relation between the change of water-level above the 



* K. Honda, Y. Yoshida, and T. Terada, Reports of the Tokyo Physico- 

 Mathematical Society, vol. ii. no. 16, p. 222; Phijs. Zeitschrift, no. 4, 

 p. 115, 1905. 



