I have been organzing Poe's works by genre, I now see. My default is chronology, but that doesn't work for Poe. He's always doing more than one thing.
For example, Penguin Classics publishes a volume entitled The Science Fiction of Edgar Allan Poe, which overlaps his entire career. This book contains, I think, very little of Poe's best writing,* but Poe really was a pioneer in the genre, so I understand the book's use. And it includes the baffling Eureka: A Prose Poem (1848), so it's valuable for that alone.
Eureka is a hundred page essay or pamphlet or meditation about science. Gravitation, electricity, the diffusion of light, astronomy, the distribution of galaxies, the formation of the solar system. Some of it is jokey, especially the first twenty pages or so, with the philosophers Aries Tottle and Hog (Francis Bacon). Some of it is highly technical and, to me, dull; the sections on gravitation and light, in particular, completely lost me. But most of it is readable, more or less, and, conceptually, at least, quite interesting.
Poe uses Eureka to make sense of all the shocking scientific discoveries of his day, particularly in astronomy and physics. Neptune had only been discovered in 1846, for example, and at the time of Eureka's publication, the tenth asteroid had just been discovered. Eureka is an imaginative engagement with these ideas and novelties, a "mental gyration on the heel" (1262). I suspect Poe thought he was also making actual scientific contributions, but the Prose Poem subtitle gave him an escape route. Actual scientists also create and work within imaginative conceptions of their ideas, but that's as close as Poe gets to actual science.
The most accessible section, for me, was Poe's attempt to understand the changes in the scale of the universe, in it's size and age and parameters. Poe imagines, for example, an angel in the path of Jupiter:
“Not unfrequently we task our imagination in picturing the capacities of an angel. Let us fancy such a being at a distance of some hundred miles from Jupiter – a close eye-witness of this planet as it speeds on its annual revolution. Now can we, I demand, fashion for ourselves any conception so distinct of this ideal being’s spiritual exaltation, as that involved in the supposition that, even by this immeasurable mass of matter, whirled immediately before his eyes, with a velocity so unutterable, he – an angel – angelic though he be – is not at once struck into nothingness and overwhelmed?” (p. 1335)
In other words, splat. NASA informs me that the mean orbital veolcity of Jupiter is 13 km/second, which one must admit is pretty fast. An irony of this jab at medieval scholasticists is that Poe's own exercise here is not so different from theirs.
Eureka is one of many contemporary examples of literary writers attempting to comprehend science. Tennyson's In Memoriam was being written around the same time, and a number of passages in Emerson's journal show his interest in actual scientific discoveries. And this is before Darwin unleashes the deluge ten years later.
I don't think Poe's concerns are particularly religious, which does set him apart a bit from Tennyson or Arthur Hugh Clough** or the like. Poe's religious beliefs, whatever they are, do not seem to be threatened. God is simply a writer, a superior version of Edgar Allan Poe:
"The plots of God are perfect. The Universe is a plot of God." (1342)
Eureka is Poe's solution to God's tricky plot.
Page references to the Library of America Poetry and Tales. The Edgar Allan Poe society puts Eureka here. And please see Poe Calendar Rob for a clearer idea of what Poe was up to.
* But don't miss "The Descent into the Maelström," which has some of Poe's best descriptive writing, or "The Facts in the Case of M. Valdemar," in which a dead man is kept alive through hypnotism, with horrible and bizarre results.
** Clough is more worried by historicist Biblical scholarship, but the idea is the same: "Matthew and Mark and Luke and holy John \ Evanished all and gone!", from "Epi-strauss-ism."