436 On the Experimental Relations [1857. 



but as the leaf is really very irregular in thickness, and ill- 

 stretched as a film, parts inclined at different angles are always 

 present at once. The light transmitted is polarized in the 

 same direction as that transmitted by a bundle of thin plates 

 of glass, inclined in the same direction. The proportion of 

 light transmitted is small, as might be expected from the high 

 reflective power of the metal. The polarization does not seem 

 due to any constrained condition of the beaten gold, for it is 

 produced, as will be shortly seen, by the annealed colourless 

 leaf-gold, and also by deposits of gold particles ; but is common 

 to it with other uncrystallized transparent substances. It would 

 seem that a very small proportion of the gold-leaf can be occu- 

 pied by apertures, since the light which passes is nearly all 

 polarized. On subjecting thin gold-leaf, or heated gold-leaf, 

 or films of gold, or any preparations which required the support 

 of glass, results of polarization were obtained, but the observa- 

 tions were imperfect because of the interfering effect of the 

 glass. 



Proceeding to employ a polarized ray of light, it was found 

 that a leaf of gold produced generally the same depolarizing 

 effect as other transparent bodies. Thus, if a plate of glass be 

 held perpendicular to the ray, or inclined to it either in the 

 plane of polarization or at right angles to it, there is no depo- 

 larization ; but if inclined in the intermediate positions, the ray 

 is more or less depolarized. So it is with gold-leaf; the same 

 effects are produced by it. Further, the depolarization is 

 accompanied by a rotation of the ray, and in this respect the 

 quadrants alternate, the rotation being to the right-hand in two 

 opposite quadrants, and to the left in the intervening quadrants. 

 So it is with gold-leaf; the same effects are produced by it, 

 and the rotation is in the same direction with that produced by 

 glass, when inclined in the same quadrant. 



As further observation in this direction was stopped by the 

 necessity of employing glass supports for the leaves, films, &c., 

 I sought for a medium so near glass in its character, as should 

 either reduce its effect to nothing, or render it so small as to 

 cause its easy elimination. Either camphine or sulphide of 

 carbon was found to answer the purpose with crown-glass ; 

 but the latter, as it possesses no sensible power of rotation 

 under ordinary circumstances, is to be preferred. Should a 



