Part 141

=Peat=, as a fuel, 262

=Pen=, first metallic (illus.), 15 first steel (illus.), 15 first metallic pen, how made, 15 how it writes, 18 invention of the, 15

=Pencils, “lead”= where from, 466 eraser is put on, 469 making description of (illus.), 467 who made the first? 466

=Periscope=, description of, 275 how we look through a (illus.), 276 mirror of, 275

=Perpetual motion=, nearest approach to, 240 is it possible? 61

=Persian rug=, antique (illus.), 167 how made, 167 imitation (illus.), 167 Kurdistan (illus.), 167 where best are made, 167

=Photographs=, of projectiles, 25

=Photography=, resultant from experiments with mirror, 22

=Piano=, pitch, 489 finishing (illus.), 484 why not more than seven octaves, 480 Dulcimer (illus.), 479 spinet (illus.), 480-481 note what it is, 490 sounding board, 488 tuning, (illus.), 484 building case around (illus.), 483 how the music gets into the, 482 clavichord (illus.), 480 instruments, musical, 488 strings, fastening on (illus.), 482 psaltery, 480 sound box, the first, 479 who made the first, 478 hammers (illus.), 483 action regulation (illus.), 484 virginal (illus.), 480-481 first (illus.), 478 tuning fork, 488 polishing (illus.), 484 sounding board, putting on the (illus.), 482 how discovered, 479 lyre, 479 octave, 480 harpsichord (illus.), 480-481

=Pickers=, boy, slate (illus.), 259

=Pictures=, with a fast camera, 39 moving, how made, 369 size of moving film, 370 never seen by the human eye, 31 taken in one five-thousandth of a second, 31

=Pin money=, why they call it? 231 how name originated, 231

=Pistols=, invented in Pistola, Italy, 46

=Plants=, corn, why it has silk? 176 do father and mother plants live together, 176 how they eat, 511 how they reproduce, 175 why do flowers have smells? 176 why they produce leaves, 175

=Plate glass=, (illus.), 246

=Portland Cement=, why called, 95

=Powder=, filling shells, 50 gun-cotton in smokeless, 35 secret of smokeless powder, 35 smokeless, 35 in submarine mines, amount of, 34

=Pressure=, generated in bore of a big gun, 54 inside of a gun at discharge, 33 in gun-barrel, resistance of, 34 of light, on scales, 37

=Primer=, invented by, 47

=Prof. Bell’s= vibrating reed (illus.), 71

=Projectiles=, photographs of, 25 arrival at target, 24 clear of smoke-zone (illus.), 30 smoke-zone, emerging from (illus.), 29 height in air from mortar, 30 impact of, from guns, 28 leaving gun muzzle (illus.), 27 travel faster than sound, 32 velocity of, 33 viewed in transit, 33 weight of, 53

=Proving grounds=, for big guns, (illus.), 53

=Pyro=, used in developing, 23

=Quarry=, cement (illus.), 96

=Quill the=, in writing (illus.), 14

=Quills=, raising geese for, 14

=Rails, steel making=, blast furnace (illus.), 234 blooming mill (illus.), 237 crane, carrying ingot, (illus.), 236 length of, 238 mixer (illus.), 234 molten steel, pouring (illus.), 236 open hearth furnace (illus.), 235 pouring side of open hearth furnace, 235 shrinkage of, 238 soaking pit (illus.), 236 temperature in furnace, 235

=Rain=, where it goes, 222 why it freshens the air, 222