There can be no doubt that the probability--the strong probability--is that the writer was on board of a ship.

And now let us consider another point.

In the case of Pondicherry, seven weeks elapsed between the threat and its fulfilment, in Dundee it was only some three or four days.
Does that suggest anything ?" "A greater distance to travel." "But the letter had also a greater distance to come." "Then I do not see the point." "There is at least a presumption that the vessel in which the man or men are is a sailing-ship.

It looks as if they always send their singular warning or token before them when starting upon their mission.

You see how quickly the deed followed the sign when it came from Dundee.