While sorting my photos from our summer holiday I came across this one on the way to Les Ecrehous islands. It shows a critical moment in the use of a transit line to navigate the potentially hazardous approach. Transit navigation works by the very simple (and totally natural) principle that if you can see any two objects lined up then you must be somewhere on an extension of that line. The approach to Les Ecrehous, northeast of Jersey in the Channel Islands is so strewn with rocks that even GPS is of limited use, since by the time it tells you you’re off course you could well be breathing brine.
Instead of one pair of markers, this part of the approach requires the navigator to line up the Bigorne rock inbetween two other rocks. Bigorne can be seen jutting up in the middle of the picture. In this part of…
