258 Mr. K. Honda on a Portable 



I have also experimentally determined this ratio by heating 

 the water in which the jar was immersed, and found O'OOI cm., 

 which agrees fairly well with the above value. The greater 

 part of the enclosed air, which is in the diving jar, is subject 

 to the daily change of temperature by 3° or 4° 0. of the sea- 

 bottom. Hence in the degree of accuracy of the present 

 tide-gaup-e, which records the motion of the mercury meniscus, 

 the correction due to the change of temperature is quite to 

 be neglected. 



To estimate the effect of the barometric change, both h and 

 T are to be considered as constant ; we then have 



dF = dIl-tlh 1 = cm + pdhJl+ S A, 



dF{ Sl {a - J tl ) + v + s 2 {b - 7i 2 ) } - P {s^cUh + s,dh 2 ) = 0. 



s 2 d/) 2 = —s^dh s . 



Eliminating dh x , dh 2 , dP, and neglecting small quantities, 

 we get 



dh s a—\ 



dU" 



M 1+ S) 



which is, in my case, nearly equal to — 0'04 mm. for the 

 change of barometric 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 1/2 mm. Thus in 

 the actual case, the correction due to the barometric change 

 is quite insensible. 



In the above calculations, I have neglected v in comparison 

 with the volume of the jar; but in the actual case, the influence 

 of v does not materially affect the above conclusions. 



On the coast at high latitude, when the sea often freezes, 

 the present tide-gauge works equally well. The tide-gauge 

 may also be used for recording the tide at sea. For this 

 purpose, it is better to suspend the recording apparatus by a 

 rope, instead of placing it on the deck of a ship. The diving- 

 jar is plunged to the sea-bottom ; if the sea be too deep, it is 

 necessary to hang the jar at a suitable depth by means of a 

 buoy fixed by a three-way anchor-rope. To avoid the distur- 

 bance of surface waves, it is required to keep the buoy itself 

 at a certain depth in the sea. 



In passing, the following remarks may be made about the 

 records obtained by my tide-gauge. Plates III. and IV. are 

 the copy of four ot' the records obtained in Kiushti. 



