330 ON A NEW STRUCTURE IN APOPHYLLITE, AND 



were shorter than those passed through by a violet one. The 

 rings exhibited a complete inversion of the Newtonian scale, 

 and the red rajs were so much more energetically acted upon 

 than the violet, that the whole prismatic spectrum was display- 

 ed in the first ring. 



In a third memoir, read before the Cambridge Society on the 

 7th May 1821, but not yet published, Mr Herschel has resumed 

 the subject of these anomalous actions upon light. " Upon re- 

 considering his results, it appeared that these specimens (viz. of 

 Apophyllite, which produced an inversion of the Newtonian 

 scale) could not be referred exclusively either to the class of at- 

 tractive or of repulsive doubly refracting crystals, nor to the inter- 

 mediate class, which is devoid of the property of double refrac- 

 tion. They appeared to belong at once to all the three classes 

 of media just mentioned, possessing the property of attractive 

 crystals, when exposed to the rays forming one extreme of the 

 spectrum, and of repulsive, in their action on the other ex- 

 treme ; while, for certain intermediate rays, they were altoge- 

 ther devoid of the property of double refraction. Mr Hek- 

 schel was led to this inference, by observing, that the curves 

 whose ordinates represented the polarising energy, after ap- 

 proaching very rapidly to the axis, would again recede rapidly 

 from it on the same side, except the ordinates were supposed 

 to become negative, which appeared more probable. This in- 

 duced him to examine the truth of his supposition, by mea- 

 sures taken in homogeneous light, and the result was a com- 

 plete confirmation of the remarkable singularity above no- 

 ticed*." 



Although we cannot doubt the accuracy of these interesting 

 results, yet it must be remembered, that the property which 



they 



* Proceedings of the Cambridge Philosophical Society, in the Edinburgh Phi- 

 losophical Journal, vol. v. p. 213. 



