6 -Art. 7.— S. Hirayania, 



room has two small windows, one at each side, the interior is suf- 

 ficiently lighted to examine or adjust the instrument and change 

 the sheet, even when the front doors are closed. The clerk is 

 advised not to leave both pairs of doors open at the same time. 

 The foundation of the building is of stone and it rests also on the 

 hard rock. The height of the floor is about two metres above the 

 surface of the sea at the highest high tide, and the cylinder in the 

 centre of the building, in which the float makes vertical motion 

 according to the state of the sea water, communicates with the sea 

 by means of a tube, far below the low tides. The bottom of the 

 cylinder itself is about five metres below the floor. The mouth of 

 the tube opens just outside the building. 



Very near the building there is a tide-staff made of stone and 

 graduated to every decimetre. This is easily read, so that a com- 

 parison of the level of the water outside and inside the cylinder 

 can be readily made ; this will also be used to record the heights of 

 the water when an interruption in the working of the tide-gauge 

 occurs. 



Only a little further from the building there is a benchmark, 

 which is connected with the precise levelling of the whole Survey 

 of the country. The height of the zero-point of the instrument is 

 accurately determined with reference to this mark, and it is 

 frequently checked. 



Tide-Gauges. 



All the tide observatories, except that at Yokohama, are pro- 

 vided with self-registering tide-gauges of some kind. For those be- 

 longing to the Land Survey Department of the Army, the instru- 

 ments are of the improved form by Sir W. Thomson (Lord Kelvin), 

 and they are constructed by Troughton and Simms. The instrument 



