LIST OF ILLUSTRATIONS.

Plate 1.—Dr. Arthur Schuster on the Spectra of Metalloids original: "Metalloids." In the 19th century, this term was commonly used to refer to non-metallic elements such as oxygen, sulfur, and chlorine..

Plates 2 to 13.—Sir William Thomson Later known as Lord Kelvin, a foundational figure in thermodynamics and electricity. on the Electrodynamic Qualities of Metals.

Plate 14.—Mr. William Crookes on the Illumination of Lines of Molecular Pressure, and the Trajectory of Molecules.

Plates 15 to 20.—Messrs. William Spottiswoode and John Fletcher Moulton on Electrical Discharges through Rarefied Gases Gases at very low pressure, often studied in vacuum tubes to observe electrical and light effects..

Plates 21 to 34.—Messrs. W. N. Hartley and A. K. Huntington on the Action of Organic Substances on the Ultra-violet Rays of the Spectrum.

Plate 35.—Mr. J. B. Hannay on the Microrheometer A device used to measure the flow and viscosity of very small amounts of liquid through narrow tubes..