A Portable A eromercurial Tide-Gauge. 



253 



The principal results which have been obtained in this 

 paper may be summarized as follows : — 



(1) The hypothesis that recombination only takes place 

 after the kinetic energy of the ions has been reduced by col- 

 lision with neutral molecules, when the ions are very near 

 each other, affords a satisfactory explanation of the variation 

 of the rate of recombination with the gas-pressure. 



(2) The results indicate that practically every ion which 

 makes a collision with four molecules becomes fixed ; that 

 most of those which make only three, and about one-sixth of 

 those which make only two, collisions, recombine. The terms 

 with fewer collisions become more important at low pressures. 



(3) The quantity obtained by dividing the coefficient of 

 recombination by the sum of the velocities of the two kinds 

 of ions, when expressed as a function of the pressure, is found 

 to depend, in the cases of different gases, on a single para- 

 meter, which is the mean free path of an ion in the gas in 

 question at some definite pressure. 



(4) An ion in carbon-dioxide at high pressures probably 

 contains the same number of gas molecules as an ion in air. 



A is a closed cylindrical 



Fig-. 1. 



XXXI. A Portable Aero-mercurial Tide- Gauge. 



By K. Honda, Rigakuhakushi *. 



[Plates III. & IV.] 



THE novel form of tide-gauge, which is a modification of 

 Richard's hydrometer, or of W. Seibt's tide-gauge f, 

 consists of a diving jar, a narrow lead (or copper) tubing and 

 a recording apparatus. 



Fig. 1 shows the diving jar. 

 vessel made of brass, 12 cm. 

 high and 12 cm. in diameter ; it 

 is screwed into a heavy lead 

 disk D. By the tube a, water 

 enters the vessel and compresses 

 the enclosed air. The vessel A 

 communicates with the recording 

 apparatus by means of a brass 

 tube b and a long lead tubing I 

 (internal diam. =3 mm. in my 

 case) ; the brass tube is bent in 

 a form as shown in the figure 

 for convenience of transporta- 

 tion. 



* Communicated by the Author. 



f Seibt, Instrumentenkunde, xvii. p. 81, 1897, 



