Ether

The ether is a 'throughly nineteenth-century notion' debated amongst the physicists of the period. It began with the experiments of Thomas Young in 1801 that demonstrated interference patterns produced by two beams of light. The notion was developed on the premise that is light travelled through a vacuum with no observable diminution of speed, then it seemed reasonable that there was some medium to carry the light. For Young, it was a stationary ether that was unaffected by the motion of material bodies or the passage of waves, a 'luminiferous ether'. By the middle of the nineteenth century ether was widely accepted amongst British physicists.

S. Connor,  'Transported Shiver of Bodies': Weighing the Victorian Ether, http://www.stevenconnor.com/ether/.