“Five knots an hour?”
“No, sir. Five knots. It’s like this ’ere. A knot ain’t a distance; it’s a speed. If I say five knots I mean five sea miles an hour.”
“A sea mile is longer than an ordinary one?”
“That’s right. It varies in different places, but you may take it as six thousand and eighty feet ’ere.”
French made a short calculation.
“That is about five and three-quarters English miles per hour,” he remarked as he scaled this distance up the Inlet from the position of the crate. And then his interest quickened suddenly.
A little over five miles from the point at which the crate had sunk the estuary narrowed to less than a quarter of a mile in width. At this point it was crossed by two bridges, carrying, respectively, the main road and the railway between Swansea and Llanelly. Had the crate been thrown from one of these?
French saw at once that no more suitable place for the purpose could be found. Objects pushed in from the bank would tend to hug the shore and to be caught in backwaters or eddies. Moreover, even if they escaped such traps they would not travel at anything like the maximum speed of the current. But from a bridge they could be dropped into the middle of the stream where the flow was quickest.
“What about the bridge up at Loughor?” he asked. “If the crate was dropped off that on an ebb tide, do you think it would get down all right?”
Manners was impressed by the suggestion. Given a good ebb, about an hour should carry the crate to where it was found. French rose with sudden energy.