LIST OF ILLUSTRATIONS. 
Plate 1.—Prof. J. Joly on the Genesis of Pleochroic Haloes. 
Plates 2 and 3. —Dr. T. R. Merton and Prof. J. W. Nicholson on Phenomena 
Relating to the Spectra of Hydrogen and Helium. 
Plates 4-18. —Dr. W. M. Hicks : A Critical Study of Spectral Series.—Part IY. 
The Structure of Spark Spectra. 
Plates 19 and 20. —Sir William Crookes on the Photographic Spectra of 
Meteorites. 
