200 LAB OR A TOR Y G U2DE IN PHYSIOLOG Y. 



paratus out of the water and lay it upon the table, 



taking care not to disturb the adjustment. 



() With dividers measure the distance from the point 

 y to line 3. This is the radius. Determine the point 

 where the circumference would cut the upper surface 

 of the rule, say point b. 



(Y) From this point determine the perpendicular dis- 

 tance to the edge of the limb at c. 



(d) The line c y x is a normal to the surface of the water 

 at the point y. The angle i is the angle of incidence; 

 the angle r is the angle of refraction. Imagine a circle 

 whose center is at y and whose circumference passes 

 through b and 3. The line b c is the sine of the angle 

 of incidence. The line x 3 is the sine of the angle 

 of refraction. 



(<?) What is the ratio of sin i to sin r, or ^ = ? 



(2) In the same manner determine the ratio of the sines 

 of these angles when the rule is so adjusted as to 

 bring a'y 6 in apparently one straight line. What is 

 the ratio of sin i' to sin r'? or - = ? 



(3) If the instrument has been carefully constructed 

 and if the determination has been made with suffi- 

 cient care, the ratios will be found to be practically 



equal, i. e., ?lLJ 5lD_L . What is the constant ratio in 

 * sin r sin r 



the case of water? This constant ratio is called the 

 index of refraction, and is conventionally represented 

 by fi. 

 For water,/* = |^ = i= 1.333. 



(4) To determine the index of refraction of glass pro- 

 ceed as in the case of water. Set the instrument upon 

 the table; the block of glass may be placed upon the 

 body of the instrument, the polished surfaces be- 

 ing placed above and below. If the distance be- 



