Your most humble Servant,
J. Smeaton.
Furnival’s-Inn Court, 12th Jan. 1758.
LXII. _An Account of the Earthquake felt in the Island of_ Sumatra, _in
the_ East-Indies, _in_ November _and_ December 1756. _In a Letter from
Mr._ Perry _to the Rev. Dr._ Stukeley, _dated at_ Fort Marlborough, _in
the Island of_ Sumatra, Feb. 20. 1757. _Communicated by the Rev._ Wm.
Stukeley, _M. D. F.R.S._
[Read Jan. 12, 1758.]
THE earthquake at Lisbon, which you gave me an account of, was
certainly the most awful tremendous calamity, that has ever happened
in the world. Its effects are extremely wonderful and amazing; and it
seems, as you observe, to have been felt in all parts of the globe.
On the 3d day of the same month the earthquake of Lisbon happened, I
felt at Manna[1] a violent shock myself; and from that time to the 3d
of December following I felt no less than twelve different shocks, all
which I took an exact account of in my pocket-bock. Since which we have
had two very severe earthquakes, felt, we believe, throughout this
island[2]. The walls of[3] Cumberland-house[4] were greatly damaged
by them. Salop-house[4], my own (formerly Mr. Massey’s), the houses
of Laye[5] and Manna, were all cracked by them; and the works at the
sugar-plantation[6] received considerable damage. The ground opened
near the _qualloe_[7] at Bencoolen, and up the River in several places;
and there issued therefrom sulphureous earth, and large quantities of
water, sending forth a most intolerable stench. Poblo Point[8] was much
cracked at the same time; and some _doosoons_[9] in-land at Manna were
destroyed, and many people in them.
These are all the ill effects, that have come to our knowlege; but, it
is reasonable to suppose, not all the damage, that has happened upon
the island.
LXIII. _Concerning the Fall of Water under Bridges. By Mr._ J.
Robertson, _F.R.S._
[Read Jan. 19, 1758.]
SOME time before the year 1740, the problem about the fall of water,
occasioned by the piers of bridges built across a river, was much
talked of at London, on account of the fall that it was supposed would
be at the new bridge to be built at Westminster. In Mr. Hawksmore’s
and Mr. Labelye’s pamphlets, the former published in 1736, and the
latter in 1739, the result of Mr. Labelye’s computations was given: but
neither the investigation of the problem, nor any rules, were at that
time exhibited to the public.
In the year 1742 was published Gardiner’s edition of Vlacq’s Tables;
in which, among the examples there prefixed to shew some of the
uses of those tables drawn up by the late William Jones, Esq; there
are two examples, one shewing how to compute the fall of water at
London-bridge, and the other applied to Westminster-bridge: but that
excellent mathematician’s investigation of the rule, by which those
examples were wrought, was not printed, altho’ he communicated to
several of his friends copies thereof. Since that time, it seems as
if the problem had in general been forgot, as it has not made its
appearance, to my knowlege, in any of the subsequent publications. As
it is a problem somewhat curious, tho’ not difficult, and its solution
not generally known (having seen four different solutions, one of them
very imperfect, extracted from the private books of an office in one of
the departments of engineering in a neighbouring nation), I thought it
might give some entertainment to the curious in these matters, if the
whole process were published. In the following investigation, much the
same with Mr. Jones’s, as the demonstrations of the principles therein
used appeared to be wanting, they are here attempted to be supplied.