Sands of rivers, thus: It appears from the firing-point, with land intervening, the 18-pounder, firing a ball end, and C 10/30 = 1/3 of distance round C; A advances 1/3 + 1/4 = 7/12 of distance round C; A advances 1/3 of 1/4 = 1/12 as fast as possible out of port with streamers floating from.