5 U :M A T R A. 
The fpring tides on the weft coafl: of Sumatra are cftimated to rife in 
general no more than four feet, as little perhaps as in any part of the 
globe ; owing to its open, xinconfined fituation, which prevents any 
i^ccumulatmn of the tide, as Is the cafe- in narro^v Teas, It is alwajrs 
high water when the moon is in the horizon, and confequently at fix 
o'clock, nearly, on the days of conjun(ftion and oppofitlon throughout 
the year; in parts not far remote from the equator^. This according to 
Newton's Theory, is about three hours later than the uninterrupted eourfe 
of nature; owing to the obvious impediment the waters meet with ixi 
revolving from the eaftward. 
* Chi'ing to this uniformity it bcconiea an cafy maltsr for the natives to afcertain the height of 
the tide nL hr,,rr rhat the moon is vifiblc Whil(> ihe appears to arceod, the water f^lUj and 
vice versA ; the lovveft of the ebb happening when £he ii in her meridian. The rule for calcu faring' 
the tides is rendered alfo to Europeaai, more firopla and pra£lical, from the fame catife. There 
only needs to add together, tlie epa£t, number of ihe niontbj and day of the month, the fnm of 
which, if under thirty, gives the moon's age — the excefs, if over. Allow forty eight minutes 
for each day, or which is the fame, take four fifths of the age, and it will give you the num- 
ber of hours after fix o'clock, at wlitch high water happens- A readinefs at this calculation is 
particularly ufcful io a country where the fea beach is the general road for travelling* 
