For the last three weeks I’ve been laying a firm groundwork for the more interesting part of the series. Perhaps there was too much time and detail: I seem to have lost much of my audience (not that the lecture hall was packed in the first place).

I’ve long believed in the importance of basic knowledge — it’s stood me in good stead through life. But I know not everyone shares my appetite for details. For what it’s worth, the rest is the fun part, where all that groundwork goes into action.

This week, trains; next week, spaceships!

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