Astronomy and telescope making. Another great hobby for a tinkerer:
I know of no subject connected with the pursuit of science which so abounds with exciting and delightful interest as that of constructing reflecting telescopes. It brings into play every principle of constructive art, with the inexpressibly glorious reward of a more intimate acquaintance with the sublime wonders of the heavens.
James Nasmyth, Engineer/Inventor, 1883
Doug