13. With two eyes how are we kept from seeing double?
14. What different purposes are served by the tears. Trace them from the lachrymal glands to the nostrils.
15. Show how the proper lenses remedy short- and long-sightedness.
16. Describe the conjunctiva and give its functions. Why should it be so sensitive?
17. How may eye strain cause disease in parts of the body remote from the eyes?
18. How does "image stimulation" differ from light stimulation in general?
PRACTICAL WORK
To illustrate Simple Properties of Light.—1. Heat an iron or platinum wire in a clear gas flame. Observe that when a high temperature is reached it gives out light or becomes luminous.
2. Cover one hand with a white and the other with a black piece of cloth, and hold both for a short time in the direct rays of the sun. Note and account for the difference in temperature which is felt.
[pg 390]3. Stand a book or a block of wood by the side of an empty pan in the sunlight, so that the end of the shadow falls on the bottom of the pan. Mark the place where the shadow terminates and fill the pan with water. Account for the shadow's becoming shorter.