SECONDARY UNDULATIONS UF OCEANIC TIDES. 11 



Hence the error arising from the change of temperature is 

 usually to be neglected. 



To estimate the effect of the barometric change, both h 

 and T are to be considered as constant ; we have then 



dP = drc — dh^ = dn + pdh. (\^-l\, 



dP\ s la - \) + y + s,{h - //,) \ - P{s,dh, -\- s.ßk) =^ 



s.ßh.j. = — Sodli^ . 



Eliminating dh^, diu, dP and neglecting small quantities, we get 



dh.i a — /i, 



dît 7-, /, 6'>, 



^H^+x) 



wliich is, in our case, nearly equal to —0.04 mm. for the change 

 of pressure by 1 cm. of mercury. Hence the barometric change 

 of 10 cm. in mercury only causes the displacement of the pen 

 not amounting to J mm. Thus in actual case, the error due 

 to the barometric change is quite insensible. 



Thus the present tide-gauge may safely be used without 

 incurring any sensible error due to the changes of temperature 

 and pressure. 



§ 3. GENERAL RESULTS. 



In the excursion of the summer vacation of 1903, we were 

 assisted by Messrs Y. Inouye, N. Watanabe and T. Hirata, 

 then students of physics and now graduates. Stations were 

 Niiyama and Ayukawa in Rikuzen ; Inuboye in Shimôsa ; 0- 

 maezaki and Maisaka in Tûtômi ; Shionomisaki in Kii ; Tei, 

 Susaki and Yotsu in Tosa. Of these stations, Ayukawa and 

 Susaki are bays, and others are open coasts. 



