As Richard Holmes points out in The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science (2009), Herschel, FRS, was a firm believer (along with Huygens) in extraterrestrial life. The Royal Society's imprimatur no doubt contributed to inspiring wider public receptiveness to the idea of life on other planets. When Encyclopaedia Perthensis asserted in 1816 that, with an atmosphere, as well as earth-like days and seasons, it was "highly probable" that Mars had its "animal inhabitants as well as our earth" (p. 614), it was stating a view that had long become commonplace.
The Romantics, then, were at home, as it were, with the idea that other planets in the solar system were populated. Indeed, it's instructive to consider that the notion of alien lifeforms is more likely to trouble religious sensibilities in our own age than it was in the early nineteenth century. As an 1827 contributor to the New Jerusalem Magazine enthused: "That [the moon] is inhabited by sensitive and intelligent beings, there is every reason to conclude, from a consideration of the sublime scenery with which its surface is adorned, and of the general beneficence of the Creator, who appears to have left no large portion of his material creation without animated existences" (p. 175). By the end of the Romantic period, astronomers routinely performed grand imaginative voltes on traditional planetary perspectives in which life on Mars could be taken for granted. As the American John Lee Comstock wrote in A System of Natural Philosophy (1830-31), intended for use in schools and academies: "To the inhabitants of Mars, our planet appears alternately as the morning and evening star, as Venus does to us" (p. 215).
It was left to "Sylvanus Urban" of The Gentleman's Magazine, reviewing William Colquitt's Essays on Geology and Astronomy in 1826, to present a more cautious view with respect to the probability of life on Mars, a view that chimes more closely, perhaps, with the current modern consensus – which, of course, Curiosity may be about to overturn: "The surface of this planet is divided into plains and mountains of strange figures, issuing volcanic fire. Apparently it is not yet formed into an inhabited world, but is what our Earth once was".
My own institution, Aberystwyth University, is currently involved in designing a Mars planetary rover as part of an European initiative planned for 2018 (ESA Aurora exploratory programme). You can see Dave Barnes of the Computer Science department testing the machine's locomotion at a local beach here. For the moment, though, the focus is on NASA's effort. As Curiosity prepares to take the Romantic project out to vexing Mars – into its dusty canyons, where the 4x4-sized vehicle will move with slow, deliberate speed beneath the high, wispy Martian clouds – let's remember those Romantic pioneers and popularizers of science.