244 Reflexion of Light at certain Metal-Liquid Surfaces. 



in the HC1 and turpentine. The results are shown in the 

 following table. In the first column are given the observed 

 values of the displacement of the centre fringe in terms of 

 turns of the compensator screw, and in the second the 

 directly observed values of 2i/r (or 2^r ). 



Comp. 2\p or 2vf/ . 



Air ... 0-7538 ± 0-0041 81°-04 + o '35 



„ 0-7549 ± 0-0018 81°'54 + 0°'19 



„ 0-7550 ± 0-0017 81°-32±0°-54 



,', 0-7548 + 00052 81°-46 + 0°-23 



„ (av.) 0-7546+0-0017 81°-34 + 0°18 



Water 9975 + 0-0035 8l°-65 + 0°-48 



09935 + 0-0010 82°-05±0°-35 



0-9934 + 00039 81°-74 + 0°-20 



„ (av.) 0-9948 + 00020 81°'81 ± 0°-16 



HC1 1-0030 + 0-0099 81°-91 + 0°-35 



Turpentine 1-0935 + 0-0069 82°-08±0°-34 



From the average values above, the values of 7r— A Cor 

 7T— A ) are computed by multiplication with the compensator 

 constant ; while the values of Q (or Q ), P (or P ), 8 (or S ), 

 8 and n' are calculated by equations (3), (6), and (8). The 

 results of the computations are given in the next table. 



A or A . Q or Q . P or P . S or S . 8. n\ 



Air 149°-73±0°-07 73°-19 148°-63 5'343 



Water 140°-10+0°-08 77°-36 139° -40 4-055 0-0084 1-329+0005 



HC1 139°-73±0°-40" 77°'58 139°-10 4-024 00086 1-340+0-015 



Turpentine. 136°-35±0°-28 78°-61 135°'78 3*693 0-0127 1'465 ±0-0 11 



Finally, samples of liquids used were put in a hollow 

 prism and their indices determined in the usual way from 

 the angle of the prism and the angle of minimum deviation. 

 The values thus obtained for ?? were 



n a . 



Water 1-3320 



HC1 1-3375 



Turpentine 1*4690 



These values are certainly correct to the third place. 



Discussion of the Results. 



An inspection of the tables just given shows that in the 

 case of each of the liquids examined, w / = t? within the limits 

 of the error of the observations. In view of what has been 

 said in the introduction and in the discussion of the theorv 



