10 SOME TIDE OBSERVATIONS AT HOBAET. 



For the purpose of more readily comprehending tlie 

 information contained in these observations, I have prepared 

 diagrams — the greater j)art drawn to scale — and setting 

 forth : — 



1st. The curve of tidal action for every day during wliich 

 observations were taken, from the 4th February to 

 the 6th March, showing the levels of high and low 

 water in comparison with mean tide level, and the 

 times at which they occurred. 



2nd. The moon's course so as to show the times of superior 

 and inferior transit of the moon's phases and apogee 

 and perigee. 



3rd. The moon's north and south, declination. 



4th. The intervals, called by Dr. Whewell " Lunitidal 

 Intervals," of time between the moon's transits and 

 the succeeding high water; the extreme intervals 

 caused by the diurnal inequality being faintly 

 marked, and the mean intervals more strongly. 



5th. Wind force and direction at every time of high water ; 

 and 



6th. Barometric pressure at every time of high water. 



The graphic presentation of all these elements synchronically 

 enables one to judge better of their influence upon the tide. 

 The diurnal inequality of spring tides is not only shown, 

 but is shown to follow the usual law, as pointed out by 

 Captain Oldham, in connection with the north and south 

 declination of the moon. Equally clearly appears the 

 occurrence of springs at greatest declination, and not at new 

 and full moon, so that at Hobarfc there is no " age of the tide ;'^ 

 and in connection with this the influence of perigee is shown 

 in the higher tides at south declination. Captain Oldham's 

 caution is very useful while looking at these diagrams that we 

 must remember that we have here only one month's observa- 

 tion. But it is not likely that a year's observations will 

 inodify the above-mentioned facts. I believe they will be 

 chiefly useful in showing that there is some regularity in the 

 sequence and circumstances of the great apparent irregularities 

 shown by these observations for one month. To show the 

 nature and extent of these irregularities I have appended two 

 diagrams shovdng for comparison a fortnight's tide curves at 

 Hobart and a fortnight's at Bombay, and a diagram repre- 

 senting a normal curve of lunitidal intervals in contrast with 

 the zig-zag mean line of such intervals at Hobart. These 

 irregiilarities will, I think, show that no " estahlisJiment," 

 that is — time of high water on the day of new or full moon — 

 can be fixed, although on the month's observations Captain 

 Oldham mentions 8h. lom. At Hobart this is of no great 



