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XXIX. On the Tides of Bombay and Kurrachee. By William Parkes, M.Inst. C.E. 
Communicated by G. B. Airy, Esq., Astronomer Boyal, F.B.S. 
Received May 5, — Read May 28, 1868. 
The tides on the coasts of India present a marked difference from those on our own 
coasts in the large amount of diurnal inequality to which they are subject. 
My attention was first directed to the subject in the course of an engineering survey 
of the Harbour of Kurrachee which I made in 1857-58, when I obtained between three 
and four months’ continuous observations, a copy of which is deposited with the Royal 
Society. Subsequently I obtained from the Admiralty, through the kindness of Captain 
Burdwood, R.N., the loan of the records of three years’ observations taken at Bombay in 
1846, 1847, and 1848. Of these I plotted in a series of continuous curves the records for 
1846, and deposited them, at the Astronomer Royal’s request, at the Royal Observatory, 
Greenwich. These records, however, are not perfect. They were made by a self-acting 
machine, the adjustment of which does not appear to have been always accurately pre- 
served ; and I hope that they will be superseded as data for investigation by a better 
record for the year 1868. Taking them as they were, however, I discussed them to 
obtain the semimonthly curves of semidiurnal tide, and also formulae for the approxi- 
mate determination of diurnal tide. 
In 1865 a careful series of observations was made at Kurrachee for the six months 
from March to August inclusive. They were made by a self-acting machine, the adjust- 
ment of which appears to have been fairly maintained, and the records are generally 
self-consistent. A register and diagram of High Water and Low Water formed from 
these observations is deposited with the Royal Society. 
This series of observations was made the basis of a discussion for the curves of semi- 
diurnal tide, and for a series of formulae for diurnal tide. 
In 1866, I received from the Secretary of State for India instructions to prepare tide- 
tables for Bombay and Kurrachee for the year 1867 ; and the tables made in accordance 
with these instructions have been compared with records of observations at Bombay and 
Kurrachee as under : 
At Bombay, from January 28th to June 4th, by direct reading from a graduated staff 
at every ten minutes, under the superintendence of Mr. Ormiston, C.E. 
At Kurrachee, the machine made diagrams for the whole year. 
The registers and diagrams of high and low water of these two records, and the con- 
tinuous curves of the Bombay observations, are also deposited with the Society. 
Plate XXXVI. is a specimen of the mode in which the times and heights of high 
and low water are exhibited in a graphic form. 
