[Illustration:
A
|\
| \
| \
| \ B RIVER
+----+--------------
| / \
| / \
| / \
|/ DOOR
STOOL
]
Draw a straight line, as shown in the diagram, from the milking-stool
perpendicular to the near bank of the river, and continue it to the
point A, which is the same distance from that bank as the stool. If you
now draw the straight line from A to the door of the dairy, it will cut
the river at B. Then the shortest route will be from the stool to B and
thence to the door. Obviously the shortest distance from A to the door
is the straight line, and as the distance from the stool to any point of
the river is the same as from A to that point, the correctness of the
solution will probably appeal to every reader without any acquaintance
with geometry.