CONTENTS. 
PART II. 
XI. Double Refraction and Dispersion in Iceland Spar: an Experimental Investigation, 
with a comparison with Huyghen’s Construction for the Extraordinary Wave. 
By R. T. Glazebrook, M.A., Fellow of Trinity College, Cambridge. Com¬ 
municated by Professor J. Clerk Maxwell, M.A., F.R.S. . . . page 421 
XII. On the Normal Paraffins. —Part III. By C. Schorlemmer, F.R.S., Professor of 
Organic Chemistry in Owens College, Manchester . 451 
XIII. On the Motion of Two Spheres in a Fluid. By W. M. Hicks, M.A., Fellow 
of St. John’s College, Cambridge. Communicated by Professor J. Clerk 
Maxwell, F.R.S . 455 
XIY. On the Organization of the Fossil Plants of the Coed-Measures .— Part X. 
Including an Examination of the supposed Radiolarians of the Carboniferous 
Rocks. By W. C. Williamson, F.R.S., Professor of Botany in Owens 
College, Manchester . 493 
XV. On the Relation between the Diurnal Range of Magnetic Declination and Hori¬ 
zontal Force, as observed at the Roycd Observatory, Greenwich, during the years 
1841 to 1877, and the Period of Solar Spot Frequency. By William Ellis, 
F.R.A.S., Superintendent of the Magnetical and Meteorological Department,. 
Roycd Observatory, Greenwich. Communicated by Sir George Airy, K.C.B. r 
F.R.S., Astronomer Roycd . 541 
XVI. On the Sensitive State of Vacuum Discharges .— Part II. By William Spottis- 
woode, D.C.L., LL.D., Pres. R.S., and J. Fletcher Moulton, late Fellow of 
Christ’s College, Cambridge . 561 
XVII. The Bakerian Lecture. — On the Photographic Method of Mapping the least 
Refrangible End of the Solar Spectrum. By Captain W. de W. Abney, 
R.E., F.R.S . 653 
