28 TEACHING SCIENCE IN THE ELEMENTARY SCHOOL

 that in the winter time when the direct rays of the sun
 strike the earth south of the equator the land still re-
 ceives more of the direct rays of the sun than do the
 northern states at the same time. It is easy to show
 the difference in the heating effects of direct and
 slanting rays by placing two pans of sand in the morn-
 ing or afternoon sun, leaving one flat and elevating
 the other slightly toward the sun. A thermometer
 thrust into the sand will record the difference in heat.

 (4) 3-III. Solar Water Heater
 Solar water heaters, frequently used in homes in south-
 ern Florida, are an excellent example of the use of the
 sun as a source of heat. The device is placed flat
 against the roof in such a position as to receive the
 most direct rays of the sun for the longest time. The
 coil or series of pipes is usually made of copper and
 is frequently painted black to increase absorption of
 the sun's rays. These pipes are usually laid on a cop-
 per plate which is also painted black. The whole device
 is contained in a flat box-like structure whose double
 strength glass lid helps to concentrate the sun's rays.
 The heated water moves into a storage tank, thus per-
 mitting more water to enter the pipes for heating.
 Even on partially cloudy days a considerable amount
 of heat reaches the pipes.

 (5) 3-V. Florida Caverns
 No school is without opportunities for studying the
 surface of the earth as an example of changes all around
 us. Specific features of the neighborhood, such as
 sand dunes, hills, washes, and caves are all centers of
 interest around which studies of the earth's surface
 may be developed. A study of the local land forms
 awakens children to the fact that the earth's surface
 is a dynamic rather than a static thing, that its form
 was not fixed in the remote past but is being developed
 and modified now.
 One good example of this type of study is the Florida
 State Caverns near Marianna. This park is in the
 limestone region of northwest Florida and holds many
 attractions with only a few man-made changes. Here
 may be observed the different kinds of rocks and their
 formations, fossils that are the remains of marine ani-
 mals, and petrified wood. In addition natural rock
 gardens, wildlife, the nature trail, historical values,