CHAPTER IV.

MATTER AND ETHER.

Inquiry regarding structure and material of the universe, 117 129

_Various hypotheses regarding matter_— (1.) Greek notion of the _Atom_, 118 130 Speculations of Lucretius, 119-130 131 (2.) Theory of Boscovich (centres of force), 131 137 (3.) Theory of infinite divisibility, 132 138 (4.) Vortex-atom theory, 133-134 139 Remarks on these theories, 135-136 141

Relative quantity of matter associated with energy, 137-138 142

_Universal gravitation_— Is a weak force, 139 144 Two ways of accounting for it, 140 145 Le Sage’s hypothesis, 141-142 146

_The Ethereal medium_— Its principal properties apparently incongruous, 143 148 Analogy of Professor Stokes, 144 149 Distortion and displacement of ether, 145 149 Inferior limit of its density, 146 150 Its supposed imperfect transparency, 147 151 Remarks on ether, 148 153

Remarks on the speculations of this chapter, 149-150 154

Modification of the vortex-ring hypothesis, 151-152 155

Possible disappearance of the visible universe, 153 157