Diurnal Tides on the Coasts of Ireland. 39 



containing a drum, over which was passed a silk cord, terminating at one ex- 

 tremity in a wooden float resting on the water, and at the other extremity in a 

 small leaden counterpoise. The motion of the water inside the case was com- 

 municated by this cord to the drum, which was connected by wheel-work of a 

 very simple character with the index-hand of a dial, marked into sixteen feet, 

 each divided into tenths. 



These dials, and the annexed wheel-work, were made by Mr. Dobbyn, of 

 Wicklow-street, Dublin, and worked remarkably well during the whole time of 

 being used. In addition to the index-hand traversing the dial, two other hands 

 were placed on a separate axle, which were pushed in opposite directions by a 

 projection placed on the index-hand, thus registering without observation the 

 maximum and minimum heights of the tide. To obtain this registry it was 

 only necessary to visit the dial twice during each lunar day, either at half-flood 

 or half-ebb ; and after a few day's practice, no difficulty was experienced by the 

 observers in recording all the High and Low Waters, with a very slight expendi- 

 ture of time. 



The greatest care was taken to secure accurate determinations of the exact 

 position of the zero marked outside the case, with reference to the Ordnance 

 and other bench-marks, the zero of the dial being made to correspond with 

 the zero outside. The gnomons by which the time was observed, were also 

 erected with care, and I believe that with good observers the error in time 

 would be less than one minute. To the observers themselves, who were all 

 selected from the coast-guards at each station, too much praise can scarcely be 

 given for the intelligence and patient industry with which they succeeded in 

 carrying out the rules for observation, in which they were carefully instructed ; 

 and I believe it is not too much to assert, that so far as the observers were con- 

 cerned, it would be impossible to have an extensive series of tidal observations 

 made with greater care and accuracy. 



Section II. — Method of Discussing the Daily Obsebvations. 



The daily observations consisted, as already mentioned, of observations of 

 all the apparent High and Low Waters occurring each day. These observations 

 of height were arranged in order of occurrence, and the Diurnal Tide in height, 

 at High and Low Water, calculated from them in the following way. 



