288 JOURNAL OF THE PLYMOUTH INS'TITUTION. 
heavy swell in the Sound, notwithstanding Sir John Rennie’s con- 
viction to the contrary. ) 
The only point Sir John Rennie seems to have undervalued in 
his report is the wash caused by the wind; but it is doubtful, 
supposing he was alive to its actual extent, if he could have 
modified his plans very much. I think not. To have made the 
Breakwater higher would have involved a greater tear and wear at 
its face, so much so that its stability might have been threatened, 
and even then it is problematical if the evil would have been 
materially influenced, not to mention cured; for the large waves 
and heavy swell roll fair into the bay through the eastern and 
western channels, and when once inside the Breakwater, are soon 
augmented by the gale to an inconvenient size. Rough water is 
particularly objectionable in our anchoring ground from the tugging 
on the cables and anchors caused by the rolling of the ship; in 
soft ground the anchors will drag before the chains break, thus 
making the situation anything but safe. 
The ground swell from the open sea is very evident at the Mill- 
bay Dock-gates after a great Atlantic storm. Here the water may 
be seen rushing like a mill-stream, either out or into the inner 
basin, in periods varying from five minutes to twelve or fourteen 
minutes; that is to say, from outrush to outrush, or the time of the 
duration of a rise and fall. These, I presume, are the remains of 
once gigantic waves worn down, only to be seen at contracted 
necks such as these gates. 
When the present Breakwater was proposed it was the main one 
of three, hence we find it referred to as the ‘‘ Great Breakwater” in 
the preliminary discussion, while the others depended on ?¢s effect 
when completed. Breakwaters from the shore opposite the eastern 
and western ends were spoken of, also one on the crest of the 
Bridge from Drake’s Island to Mount Edgcumbe for the especial 
protection of the Hamoaze. This breakwater was discussed and 
dismissed by Sir John Rennie on account of its dangerous inter- 
ference with the currents at the entrance to the Hamoaze. No one 
can doubt that such a barrier on the Bridge would have entirely 
altered the currents, especially on the latter half of flood tides and 
the first half of ebbs, by causing a perfect deflection of the mass of 
water, and necessarily an area of disturbance similar to Devil’s 
Point, where more than ordinary caution is necessary to keep from 
danger during a strong tide. But at present the large and, as the 
