Part 144

=Sky=, will it ever fall? 255 why is it blue? 253

=Soap=, lye in, 411 palm olive oil in, 411 what made of, 411

=Soda=, Leblanc process, 494 Solvay process, 494 where we get, 494

=Solids=, definition, 348

=Some= wonders of the human body, 311

=Sound=, deadening of, 79 first over a wire, 71 how measured, 242 how produced, 485 speed of, 140-486 travels through air slowly, 31 in a sea shell, 79 what is, 78-485 waves, 79 waves, length of, 487 where comes from, 78

=Slate pencil=, why cannot write on paper with, 18

=Sleep=, where are we when, 365 with eyes open, why we cannot, 92 ghosts, 367 why heart beats during, 191 why we go to, 365 restless, 92

=Sling=, man in action (illus.), 41 how first made, 41

=Slings=, and their drawbacks, 42

=Slow match=, of early firearms, 45

=Smells=, why do flowers have, 176

=Smoke-cone=, in gun-firing (illus.), 28

=Smokeless powder=, 35

=Smoke-rings=, hard as steel, 27

=Smoke signals=, of Indians, 412

=Smoke-zone=, in gun firing, 111

=Sneezing=, what makes us, 194 why do we, 194

=Snowflakes=, what makes them white? 409

=Space=, extends, how far, 256

=Sparkle=, when merry, why eyes, 92

=Spear=, as a weapon, 42

=Specific gravity=, meaning of, 268

=Speed=, of light, 36

=Spinneret=, of the silkworm, 115

=Spinning wheel=, in making cloth from wool, 81

=Sponge=, capillary attraction of, 18

=Sponges=, breeding time of, 286 how do they grow? 286 how they eat, 287 how they are caught, 287 where they come from? 286