reflected, refracted, polarized, and twisted, in the same way as ordinary light-waves can be, and that the laws of optics are applicable to both. CHAPTER II PROPERTIES OF MATTER AND ETHER Properties of Matter and Ether compared--Discontinuity _versus_ Continuity--Size of atoms--Astronomical distances--Number of atoms in the universe--Ether unlimited--Kinds of Matter, permanent qualities of--Atomic structure; vortex-rings, their properties--Ether structureless--Matter gravitative, Ether not--Friction in Matter, Ether frictionless--Chemical properties--Energy in Matter and in Ether--Matter as a transformer of Energy--Elasticity--Vibratory rates and waves--Density--Heat--Indestructibility of Matter--Inertia in Matter and in Ether--Matter not inert--Magnetism and Ether waves--States of Matter--Cohesion and chemism affected by temperature--Shearing stress in Solids and in Ether--Ether pressure--Sensation dependent upon Matter--Nervous system not affected by Ether states--Other stresses in Ether--Transformations of Motion--Terminology. A common conception of the ether has been that it is a finer-grained substance than ordinary matter, but otherwise so like the latter that the laws found to hold good with matter were equally applicable to the ether, and hence the mechanical conceptions formed from experience in regard to the one have been transferred to the other, and the properties belonging to one, such as density, elasticity, etc., have been asserted as properties of the other. There is so considerable a body of knowledge bearing upon the similarities and dissimilarities of these two entities that it will be well to compare them. After such comparison one will be better able to judge of the propriety of assuming them to be subject to identical laws. 1. MATTER IS DISCONTINUOUS.