It has now the well-known reputation of being the best frequented watering place on the east coast of Scotland.
TIDAL SCOUR.
In the report, of 1814, on Dundee we find the following remarks on tidal scour:—
“To put this matter in a clearer point of view, let us see what nature does upon the great scale, as for example in the extensive basin forming the Firth of Tay. We there find that in consequence of the rapidity of the current at the narrow passage in the neighbourhood of Broughty Castle, which may be viewed as the scouring aperture of the basin of the Tay, the water is from forty to eighty feet in depth, and moves with a velocity which carries a great quantity of sandy particles along with it. But no sooner are the waters of this current allowed to spread and cover the basin of the Tay, than the velocity ceases, and the foreign matters fall to the bottom and form the various sandbanks which appear at low water. In a similar way the deposition of silt and earthy particles brought down the river in speats is accounted for. Now, this view of the case is equally applicable to the harbour of Dundee, for so long as the water preserves the velocity it acquires in the scouring apertures or arches in the quays, it carries all its foreign matters along with it; but the moment it is allowed to expand over the extent of the harbour the deposition of these earthy particles begins. And in every case the well-known law in hydraulics holds good, that the scouring effect of a fluid is in the ratio of the square of the velocity.”
UNSCREWING OF BOLTS.
The following observations made in 1807 on the action of the waves in unscrewing bolts, are interesting:—
“The unlocking of screws, where washers had been introduced as a security was rather unexpected, and the writer took an opportunity of conversing with his much respected friend Professor Playfair regarding this circumstance. The Professor observed, that he had experienced some inconvenience of this kind from the unlocking of almost all the screws of a telescope which had been sent to him from London by the mail coach. Indeed, from the spiral form of the screw, which is, in fact, an inclined plane, Mr. Playfair readily accounted for such an occurrence, and, when reflected upon, it seems to be an effect rather to be looked for, and is a reason why riveting the point of a bolt in preference to screwing it should generally be resorted to, where much motion is to be apprehended.”
CEMENT RUBBLE COFFERDAMS.
I give his description of the cement rubble cofferdams, first used in 1808, at the erection of the Bell Rock Lighthouse:—
“At seven o’clock this morning, the tide proving more favourable, the artificers began to work. At nine o’clock the rock was again overflowed, and the boats returned to the tender after two hours’ work. Part of the operations of this morning’s tide consisted in building up the crevices and inequalities of the rock round the margin of the foundation with Pozzolano mortar and the chips produced from excavation, with the view to dam out the water. These little walls varied from six to eighteen inches in height; a small sluice or aperture being formed in one of them, by which the water, during ebb tide, was allowed to drain off.