In 1750, astronomer Thomas Wright estimated the number of inhabited planets in the observable universe:

Of…habitable Worlds, such as the Earth, all which we may suppose to be also of a terrestrial or terraqueous Nature, and filled with Beings of the human Species, subject to Mortality, it may not be amiss in this Place to compute how many may be conceived within our finite View every clear Star-light Night. It has already been made appear, that there cannot possibly be less than 10,000,000 Suns, or Stars, within the Radius of the visible Creation; and admitting them all to have each but an equal Number of primary Planets moving round them, it follows that there must be within the whole celestial Area 60,000,000 planetary Worlds like ours. And if to these we add those of the secondary Class, such as the Moon, which we may naturally suppose to attend particular primary ones, and every System more or less of them as well as here; such Satellites may amount in the Whole perhaps to 100,000,000, or more, in all together then we may lately reckon 170,000,000, and yet be much within Compass, occlusive of the Comets which I judge to be by far the most numerous Part of the Creation.

He adds, soberly, that to the Creator the apocalypse of single world may be a mundane matter:

In this great Celestial Creation, the Catastrophy of a World, such as ours, or even the total Dissolution of a System of Worlds, may possibly be no more to the great Author of Nature, than the most common Accident in Life with us, and in all Probability such final and general Doom-Days may be as frequent there, as even Birth-Days, or Mortality with us.

The book—An Original Theory or New Hypothesis of the Universe—was the first to posit the idea of a disc-shaped Milky Way.