Abstract: A direction indicator includes a base defining four edges that extend parallel to a horizontal surface on which the base is placed and form portions of respective sides of a rectangle, a bearing indicator which is selectively positionable on the base for carrying compass bearing information, and a gnomon supported in a predetermined position relative to the direction indicator. The bearing indicator may further contain time markings in the event that it is used as a sundial. The base is adapted to be placed in a predetermined orientation on a horizontal surface. For a given orientation of the base, the direction indicator can be appropriately positioned relative to the base by reference to the direction of a shadow cast by the gnomon at a predetermined time of day and by reference to the bearing of the sun at that predetermined time of day.

Abstract: An apparatus for illustrating the operation of an Archimedes screw. Two passages (8,9) are defined which together form a single closed loop passageway. A first passage (8) is generally linear and a second passage (9) is of helical form and is connected at its ends to the ends of the first passage. The walls of the two passages are transparent such that the movement of fluid (10) can be clearly seen. The first and second passages are arranged such that if the first passage (8) is positioned at a predetermined inclination to the vertical fluid can be transferred through the second passage (9) from the lower to the upper end of the first passage by rotating the apparatus about an axis extending parallel to the length of the first passage. The second passage (9) may be in the form of a helical tube wound around the outside of a straight tube defining the first passage (8) .