How much more do you know about pneumatic tools than Father Neptune does? No doubt you've used a "pneumatic" tool of a sort yourself more than once--a tool for making a noise. Guess what. A pop-gun! Look up _pneumatic tools_, and you will find that the same thing that makes the pop-gun pop helps to build skyscrapers, locomotives, and steamships, and do a lot of other wonderful things. In connection with the water wedges made by the sea you must remember that curious trick ice has when it freezes (page 154); otherwise you can't understand how it could act like a wedge. Yes, and wedges, simple as they look, are almost as wonderful as levers; and you know what Archimedes said he could do with a lever. The whole subject of machinery and particularly of "automatic" or so-called self-acting machinery[52] is fascinating. Find out about planing mills and how they work, particularly why they stop planing just when they are told to. [Footnote 52: As a matter of fact, the only machinery that is really automatic is the machinery of nature, of which what we have called "the machinery of the sea" is an example.] In connection with how the sea sometimes helps make harbors think of as many great harbors as you can, and then look on your geography map and see how many you have missed. What character in "Titus Andronicus" says that about the man standing on a rock and watching the sea come to eat him up? Your geography has a good deal to say about continental shelves; and with pictures. Do you remember? Speaking of lands sinking under the sea you'll run into a world of interesting things if you look up the story of the Lost Island of Atlantis; about the Egyptian priest who first described it to Solon, the Greek lawgiver, as an earthly paradise where all the laws and everything else were just right. And if you're of High School age you'll enjoy reading what Plato[53] and Homer[54] say about this ideal land. [Footnote 53: Timæus.] [Footnote 54: The Odyssey.] Isn't it a striking thing how the big sea that can look so fierce takes such tender care of the little coral people? And what extraordinary folks these coral people are! Any good article about them will tell you worlds of interesting things. For instance, you will find the people of whole villages living together with only one backbone. I mean not one backbone _apiece_ but one backbone among them _all_! And they have the queerest way with their stomachs, a kind of co-operative digestion, of co-operative housekeeping. (Your mother will be particularly interested in this because it shows the "community kitchen" idea has been thoroughly tried out and it works! If you don't know about "community kitchens" among human housekeepers ask mother to tell you, and then you tell _her_ what you found out about these strange little housekeepers of the sea.) CHAPTER XI