372 Transactions of the Society. 



valve of considerable thickness or where two membranes lie 

 parallel to one another, the fact would be shown by interference 

 bands running the length of the diffracted spectra. The last deter- 

 mination carried out by this method is the investigation of the 

 possible ratio of the size of the marking to the distance between 

 neighbouring markings. 



The method here described in its application to the study of 

 diatom structure, may be used with equal facility for the investiga- 

 tion of the polarization and spectro-photometric properties of 

 microscopic objects. 



