1897] MICROSCOPICAL JOURNAL. 155 



The Index of Refraction. 



By Dr. B. L. RAWLINS, 



D VLLAS, TEXAS. 



A ready, fairly accurate and practical method of deter- 

 mining the index of refraction of liquids, and transpar- 

 ent solids with plane parallel sides, would be of interest 

 possibly to the majority of workers. 



The works on optics and the elementary treatises on 

 how to work with the microscope, cipparently lose sight 

 of the necessity for something practical, in giving us com- 

 plicated formulas nnd describing e.xpensive instruments 

 for determining this index. 



It is with this apology that the writer offers this arti- 

 cle, feeling sure that the same thin<^ must have occurred 

 to many, although he has never seen this method pub- 

 lished. 



As in passing from a rarer to a denser medium, a ray 

 of light is deflected in a definite direction from its im- 

 raergent course, likewise is the apparent distance through 

 the denser medium less than the real distance. 



As the ratio of the sin. of the angle of incidence to 

 the sin. of the angle of refraction is constant, likewise is 

 the ratio of the apparent distance through the denser 

 medium to its real distance invariable. 



From experiment it is found that as many times greater 

 than the sin. of the angle of refraction is the sin. of the 

 angle of incidence, so many times greater is the real dis- 

 tance through the denser medium, than the apparent 

 distance. 



For exami)le the angle of refraction of water is 1.333: 

 the apparent depth of a volume of water one and one- 

 third feet in actual depth, is one foot. 



Assuming that the worker interested in this subject is 

 possessed of a microsco})e with accurate adjustment and 

 a graduated micro-millimeter fine adjustment screw, he 



