39 COORDINATION AND SENSATION 



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. 



4. Place a coin in the center of an empty pan and let the members 

 of the class stand where the coin is barely out of sight over the edges 

 of the pan. Fill the pan with water and account for the coin's coming 

 into view. Show by a drawing how light, in passing from the water 

 into the air, is so bent as to enter the eye. 



5. With a convex lens, in a darkened room, focus the light from a 

 candle flame so that it falls on a white screen and forms an image of 

 the candle. Observe that the image is inverted. In a well-lighted 

 room focus the light from a window upon a white screen. Show that, 

 as the distance from the window to the screen is changed, the position 

 of the lens must also be changed. (Accommodation.) 



6. Hold a piece of cardboard, about eight inches square and having 

 a smooth, round hole an eighth of an inch in diameter in the center, in 

 front of a lighted candle in a darkened room. Back of the opening 

 place a muslin or paper screen (Fig. 157). Observe that a dim image 

 is formed. Account for the fact that it is inverted. Hold a lens 

 between the cardboard and the screen so that the light passes 

 through it also. The image should now appear smaller and more 

 distinct. 



To prove the Presence of the Blind Spot. Close the left eye and 

 with the right gaze steadily at the spot on the left side of this page 



FIG. 1 66. Diagram for proving presence of the blind spot. 



(Fig. 166). Then starting with the book a foot or more from the face, 

 move it slowly toward the eye. A place will be found where the spot on 

 the right entirely disappears. On bringing it nearer, however, it is again 

 seen. As the book is moved forward or backward, the position of the 



