MR. WILLIAM PARKES ON THE TIDES OF BOMBAY AND KURRACHEE. 695 
Appendix. 
Explanation op the Diagrams. 
PLATE XXXVI. 
The four sets of waving lines running the whole length of the diagrams represent 
respectively High-Water Times, Low-Water Times, High-Water Heights, and Low- 
Water Heights. 
The observed times are represented by small black circles, the day and approximate 
hour being given by their positions measured along a horizontal line, and their intervals 
after the moon’s transit by their vertical positions according to the scale — the line A A 
representing thirty-three hours after the moon’s transit throughout. 
The observed heights are also marked by small black circles laid off by scale from the 
straight horizontal line B B, which represents mean sea-level. The diurnal inequality is 
shown by the widths of the spaces between the lines joining alternate black circles — 
coloured brown in the manuscript diagrams. 
The blue * lines passing along the centres of these spaces represent the actual curves 
of semidiurnal tide. The uneven line B B is equidistant between the semidiurnal curves 
of High-Water and Low-Water heights, and represents the actual half-tide level. 
Mean sea-level at Bombay is deduced from the four months’ observations here given, 
and is 80 feet 4 inches above the “ Town Hall Datum.” 
Mean sea-level at Kurrachee is deduced from the observations of 1857-58, and is 
4 feet 9 inches above the “ Harbour Works Datum.” 
The calculated times and heights are given by redf circles in the diagrams for 1867. 
The heights are plotted from the actual half-tide level (uneven line), and not from the 
mean sea (straight line). 
The calculated semidiurnal curves of time and height are shown by red J lines. 
The Bombay observations (1867) are believed to be sufficiently correct for most 
practical purposes. The same may be said of the Kurrachee observations of 1857-58. 
The Kurrachee observations of 1865 and 1867 were taken by a self-registering 
machine at a spot a mile and a half higher up the harbour than that at which those 
of 1857-58 were taken; but numerous observations have been taken simultaneously at 
the two places, which prove that the tide-wave is scarcely appreciably affected in its 
passage up the harbour. The time of high water is, however, from five to ten minutes 
later at the upper station. The times of high and low water given on the diagrams of 
1865 and 1867 are ten minutes earlier than those actually recorded, so as to make them 
comparable with those of 1857-58. 
The working of the self-registering machine is not quite perfect, and its adjustment is 
* Strong black lines. f Small open circles. J Broken black lines. 
