60 Proceedings of the Royal Irish Academy. 



(8) Normal and abuoimal types of dissymmetry have been observed ; and 

 the result obtained by the study of tungsten and molybdenum, namely, that 

 there is a connexion between the rotation of the plane of polarization and the 

 type of dissymmetry, has been confii-med for this substance. 



With much pleasure I take this opportunity of expressing my cordial 

 thanks to M. Deslandres, Director of the Observatory at Meudon, Paris, for 

 his great kindness in setting the apparatus necessary for the completion of 

 this research at my disposal. 



