<p><strong>Fig. 3.19.</strong> A floating object keeps the drifter from sinking. A neutrally buoyant object or underwater sail allows the drifter to be pulled by the current. A weight makes sure the neutrally buoyant object or sail does not float to the surface.</p>

Fig. 3.19. A floating object keeps the drifter from sinking. A neutrally buoyant object or underwater sail allows the drifter to be pulled by the current. A weight makes sure the neutrally buoyant object or sail does not float to the surface.

Image by Byron Inouye