408 



Tratisactioiis. 



Board. It was erected in 1887, and is at present situated in N shed, on 

 Jervois Quay, Wellington, as shown in fig. 1. 



The general design of the gauge is shown in fig. 2. The cylinder or 

 drum is 4 ft. long and 0-4 ft. in diameter.* It is horizontal, and carries a 

 wheel 2-4 ft. in diameter on the end of its axle. The float is attached by 

 a band to the circumference of the wheel. A smaller wheel carries a 

 counterweight to keep the float-band always taut. The pencil-carriage 

 moves horizontally at a uniform rate, and is in train with the driving-chain 

 of the eight-day lever clock. Its motion is approximately 6 in. a day, so 

 that one week's record is obtained on the drum. 



It will be seen that the design of this gauge avoids all the defects of the 

 Newman and other forms of gauge. Thus, owing to the smaller diameter 

 of the drum, it can be readily turned truly circular, and, as it is the amount 

 of motion under the pencil that has to be measured, small ellipticity of 



3f< 



Floit 



ScsU of Feel 



Fig. 2. — The Wellington Self-eegistering Tide-gauge. 



section does not vitiate the record, and, althovigh the drum is naturally 

 turned as evenly as possible, any defect in balancing is immaterial, as the 

 counterweight can be adjusted to overcome it. It is, however, in the ad- 

 justment of the time that the greatest improvement becomes apparent. 

 The clock is wound up once a week, and when wound up the pencil-carriage 

 is drawn to the left end of the drum. A new record-paper is attached to 

 the drum, which is then revolved underneath the pencil, and on the line so 

 drawn the correct local mean time is written, independent of what time is 

 shown on the clock. At the end of the week the drum is again turned round, 



* Tiie range in Wellington is about 4 ft. or 5 ft., so that wlien used elsewhere the 

 ratio of the diameters of the drum and wheel must be altei-ed to keep the record within 

 practical limits. 



