b K. HONDA, T. TERADA, Y. YOSHIDA, AND D. ISITANl. 



sea, *S^^ and S_^ be the cross sections of A and B respectively, 

 then tlie pressure P of the water on the surface of mercury in 

 A is given by 



when 7t is the atmospheric pressure and p the density of mercury. 

 We have also the equation of continuity, 



S-, dh_ = — S:i dh-^ ; 



taking the differential of the first equation, we have 



dli, — dJt^ — p [dli-i — dh-^^ ; 

 eliminating dli, , we get 



dih 1 



This reduction-factor was nearly tV in our tide-gauge. The pre- 

 sent apparatus Avorked very satisfactorily, when it was possible 

 to set the instrument near the shore and the height of the 

 mercury in ^1 or B above sea level did not exceed 1 or 2 meters. 

 The practical difficulty, however, met with in our excursion 

 was that it was often necessar}^ to set up the apparatus at 

 high stations, where the sucking was difficult and the air dis- 

 solved in Waaler frequently gathered in the vessel A, and caused 

 an unusual rise of the pen. To avoid these inconveniences, 

 another arrangement has l)een used since the winter excursion 

 of lOOo. It is in fact a modification of LUchard's tide-gauge ; 

 in our case, his recording arrangement was replaced by ours, 

 and the caoutchouc -bag in his diving jar was dispensed with. 

 Our diving jar is shown in Fig. 3. A is a closed cylindrical 

 vessel made of brass, 12 cm. high and 12 cm. in diameter; it 



