HOMOGEXEOUS FUJIDS BY POLARIZED LIGHT. 47 



nary polarized light, and are only different in kind. Now here 

 is another characteristic difference between the action of crystal- 

 line laminae and that of oil of turpentine. Light thus modified 

 is no longer coloured by this liquid, and appears, when subjected 

 to this trial, as completely depolarized as when caused to pass 

 immediately through a rhomboid of calcareous spar. 



At the extremity of a tube C^'SO in length, filled with oil 

 of turpentine, I placed a glass parallelopiped, in which the inci- 

 dent rays, previously polarized, suffered two complete reflexions 

 in a plane inclined at an angle of 45° to that of primitive polar- 

 ization. In looking through the other extremity of this tube 

 with a rhomboid of calcareous spar, I could perceive no trace of 

 colorization, when the rays had been reflected at a proper inci- 

 dence in the glass parallelopiped, whilst polarized light which 

 had not suffered this modification gave rise in the same tube to 

 the most vivid colours. Rock-crystal cut perpendicularly to the 

 axis produced under these circumstances the same effect as 

 oil of turpentine. 



Polarized light, modified by double total reflexion, being no 

 longer coloured in this fluid, analogy indicates that it should no 

 longer produce more than a single system of fringes with the 

 apparatus described above, and this is confirmed by experiment. 



It is natural to conclude from these two experiments, that 

 light thus modified suffers only a single refraction in the oil of 

 turpentine. To verify this conclusion, and to assure myself that 

 the light on leaving the tube really did not contain more than a 

 single system of fringes, I made it traverse a thin crystalline 

 lamina, and I then saw that it gave rise to the same colours as 

 when it had not traversed the oil of turpentine, or at least the 

 tints differed very little, and this slight difference was due to the 

 peculiar colour of the liquid, as was seen by causing incident 

 light to traverse this fluid before its primitive polarization. 



But here is another sufficiently remarkable experiment, which 

 shows perhaps still better, that in the present case the oil of tur- 

 pentine gives up the light just as it received it. When the po- 

 larized rays have suffered total reflexion in an azimuth of 45° 

 to the primitive plane of polarization, if they are again submitted 

 to two total reflexions in a second glass parallelopiped, they 

 reassume all the appearance and properties of complete polar- 

 ization ; this is a pha^nomenou easily explained upon the theory 

 put forth in my last memoir. But the same phjenomenon still 



