Sentence:  The whole matter of the univerſe may be divided into atoms and <WSD>æther</WSD>. ... The latter, <WSD>æther</WSD>, is a ſubtile elaſtic fluid, whoſe particles have a continual tendency to ſeparate or fly off every way, unleſs impreſſed by ſome body: This <WSD>æther</WSD> ſurrounds each atom like an atmoſphere, and preſſes equally towards the center of each. 
Meaning of the word marked with <WSD> tags:  "Often as" '''(aether)''' "and more fully as" '''(luminiferous aether)''': a substance once thought to fill all unoccupied space that allowed electromagnetic waves to pass through it and interact with matter, without exerting any resistance to matter or energy; its existence was disproved by the 1887 (Michelson–Morley experiment) and the theory of relativity propounded by (Albert Einstein) (1879–1955).