British hard SF in AD 1900

Apropos of nothing, I'm considering what an interplanetary explorer born along the River Thames might be expected to know before his flight. This, after Maxwell and before the Special Relativity, so: here's my range.

(Wow, the Bagestan has discovered STEAMPUNK!!, I hear my readers saying. Yeah yeah.)

First up is an almanac of 1900. This mainly agrees with A Handy Book of Reference on All Subjects, which is what it says it is. The units are Imperial. The data are... accurate, within two orders of magnitude. In fact there was even a calculation by one CT Whitmell so as to get some eclipse-observations done of the Jovian moons upon Jove.

It follows that anybody writing SF in the later Victorian era should have known, from Kepler, Jupiter's mass and therefore density. And Saturn's mass and density, and I must assume Uranus' and Neptune's. Also known, by inverse-square, would be the insolation they all get from our Sun as a fraction of Earth's. [PEDANTRY 1/29/23: - assuming the outer planets where we simplify the Solar disc to a point.]

These moons lacking their own moons might be tricky to get a mass from, but their masses can at least be constrained; the innermost Jovians are Laplacian (not Keplerian) so might have been better constrained. Mind, the densities of Ganymede and Callisto were better than those calculated for Io and Europa - which were too low.

All these moons should have had their surface-gravity and escape-velocities approximated; all should have been ruled out as habitable upon their surface. Titan, yeah; this is cold enough and unconstrained enough that atmosphere be allowed (but of what...?)

On the other hand, I don't think anyone considered the tidal-forces exerted upon Io and Europa before this classic. Maybe Io could be assumed a cold but earthquakey rock; Europa might have had that underice ocean already.

As for getting from place-to-place, the Rocket Equation remained unknown. As for keeping the atmosphere in and lowering unnecessary mass, nobody had a clue about Carbon Fibre. That's where unobtainium comes in.

And the scope of unobtainium really was high in the steampunk days. Michelson and Morley although known weren't yet digested. For instance - what's gravity? (As if we know any better in 2022.) It should relate to Maxwell's electromagnetism as a spooky force but how? and does it follow the speed of electromagnetic waves? So a speculative writer would be forgiven for assuming that although a "Light Year" exists, that ain't stopping a trip to - say - the Sirius system (known as a binary). More than we'll forgive our contemporary hypesters.