Among Archimedes' inventions was a device called the Archimedean screw, which was designed to draw water from a low-lying body of water up a hill into an irrigation ditch.
Why am I talking about this invention instead of my traditional steam-y fare?*
The short answer is that Alaskans and Australians are evil idea-generators.
The somewhat lengthier answer can be traced back to this post and this post. For background, in case y'all haven't read the posts from last night and Wednesday, Gary and Stephanie hijacked the comments of my post on Wednesday to discuss fighting the Final War of the Roman Republic (the Roman Civil War) with steam power as a factor.
And of course, as my faithful blog readers know, I'm not one to resist a thought experiment such as this.
Anyway, back to Archimedes. The screw was designed to move water uphill through rotating on a fixed point. Water started moving as soon as the screw did, and if any water fell back down the hill, it was immediately caught and moved up again. Now, we can extrapolate this out further and theorize that, if you built a large version of the screw, set it on a horizontal plane and affixed it to something solid -- say a Roman trireme -- this water movement could, in theory, move the vessel in a straight line with a minimum of manual labor.
Mount two Archimedean screws on the vessel, and you have the start of mechanical propulsion. The only constraint here is that the screws have to run either the length of the vessel or slightly longer in order to generate enough water movement to speed the vessel along. Otherwise, you've got a mechanically powered Roman vessel using technology that was already in use during the final days of the Roman Republic.
The above is also how my tech considerations for my other steampunk stories works. It can all be distilled down to a) Does the theory exist? and b) How feasible is it given the materials that are present?
Oh, and Stephanie and Gary? If you've emailed me since roughly 9 am EST, I'll get back to you both sometime tonight. Access to my gmail account from my office computer gets cut off after that time.
* Like the pun? I'm quite proud of it.