188 Mr. G. Pierce on Indices of 



diagram here given (fig. 7), to avoid confusion of lines, only- 

 Curve II. is shown. 











Fig. 7. 











110 





































■a ioo 



















nie 



















1-1 90 

















■-5 



















"3 so 

 Ph 





































70 





































11 12 13 14 



Heading of Distance in centimetres. 



The following table contains the location of the nodes, their 

 displacement, and the calculated values of the index of 

 refraction; 



Curve. 



Thicknes3 of 

 Paraffin 

 in mm. 



Position of 

 the Node. 



13-87 

 13-30 

 1238 

 12-28 



Displacement 

 in mm. 



». 



1-53 

 1-58 

 1-59 



V 



(Air) 



10-7 



25-5 



O'l 



14-9 

 15-9 



II 



Ill 



IV 



28-4 





Mean value of the index of refraction of the paraffin 

 = 1-56. 



It is seen that the distance between the second and third 

 nodes of the air-curve is 2*23 centim., which is in good 

 agreement with the value 2*21 previously obtained for the 

 half wave-length. 



The specimen of paraffin employed in this experiment had 

 a melting-point of 56° C. The three thicknesses were cut 

 from the same block, but no precautions were taken to pre- 

 vent them from absorbing moisture from the atmosphere, 

 which might well account for the 'discrepancy in the three 



