Hydraulic models solve differential equations. They aren't bad , but modern computers are a much better computational environment.

There's a fairly significant overlap between engineers and economists. Chemists and physicists also.

Largely out of the economic mainstream, since the 20th century, sadly.

I got a Kindle for Christmas, and I've been reading through Discworld chronologically. I'm on Raising Steam right now, and I already feel like I'm going to have to reread the series with a list of references open. There were a lot of places where it was apparent there was a reference to something, but it was completely inaccessible as an American in his late 20's.

At the same time, I almost feel like I shouldn't read the last book for a while, it's going to be really bittersweet.