686 MR. WILLIAM PAEKES ON THE TIDES OE BOMBAY AND KURRACHEE. 
The discussions of the records for semidiurnal tide were made in the ordinary manner, 
except that diurnal inequality was eliminated before grouping the heights and intervals. 
The curves of semimonthly inequality are appended (Plate XXXVII.), and the principal 
results are as follows : — 
Bombay. 
Kurrachee. 
Time of highest tide of the springs after | 
the transit nearest to noon or midnight) 
d h m 
1 12 17 
d h m 
1 11 3 
Mean of least lunitidal intervals 
1 11 32 
1 10 10 
Mean of greatest lunitidal intervals . . 
1 13 6 
1 11 42 
Mean spring half-range 
73 inches. 
44 inches. 
Mean neap half-range 
H|S) 
CO 
CO 
22 
The effects of the variations of declination and parallax in semidiurnal tide have not 
been minutely investigated ; but it was found that the corrections for moon’s parallax 
adopted by the Admiralty, for tides of similar range on the English coast, were insuffi- 
cient. The following were therefore adopted in the calculations of height of semidiurnal 
tide. 
For all times of Moon’s transit. 
Parallax. 
Correction. 
Parallax. 
Correction. 
Bombay. 
Kurrachee. 
Bombay. 
Kurrachee. 
inches. 
inches. 
571 
inches. 
inches. 
54 
— 10 
-7 
+ 2 
+ 1 
541 
- 81 
—51 
58 
+ 31 
+ 2 
55 
- 7 
— 4 
581 
+ 51 
+ 31 
551 
— 5 
— 3 
59 
+ 71 
+ 5 
56 
- 31 
—2 
591 
+ 9 
+ 61 
56| 
- 2 
— 1 
60 
+ 11 
+ 8 
57 
0 
0 
601 
+ 13 
+ 91 
61 
+ 15 
+ 11 
I now proceed to describe those features which it is the special object of this commu- 
nication to bring before the Royal Society, viz. those in which the tides on the coasts 
of India differ most remarkably from those on our own coasts. 
It is well known that certain effects are produced by the attraction of the sun and 
moon upon the waters of the ocean, which ultimately result in a series of tide-waves 
having an average length or period of half a lunar day. The combination of the solar 
and lunar waves as the luminaries change their relative positions, produce the alterna- 
tions of neap and spring tides. Without entering into any question of tidal theory, it 
may be assumed that the semidiurnal tide-wave is primarily due to the tendency of the 
waters to be drawn into two heaps, one on the side of the earth nearest to the attracting 
body, and the other on the side furthest from it. When the attracting body is in the 
plane of the equator, these two tendencies appear to be sensibly similar *, and the resulting 
* A slight difference in the tides following the north and south transits has been detected by Mr. Bxjnx in 
the Bristol tides (Philosophical Transactions, 1867). 
