Though, in these cases, the direction taken by any one whale be straight as a surveyor’s parallel, and though the line of advance be strictly confined to its own unavoidable, straight wake, yet the arbitrary _vein_ in which at these times he is said to swim, generally embraces some few miles in width (more or less, as the vein is presumed to expand or contract); but never exceeds the visual sweep from the whale-ship’s mast-heads, when circumspectly gliding along this magic zone.