364 



OUR PHYSICAL WORLD 



Musical instruments, 325 

 Musical scale, 333 



Negative, photographic, 320, 321 



Neon, 167, 170 



Neptune, 2, 7, n 



Newcomen's engine, 179, 180 



Nights, length of, n 



Niter, 51 



Niton, 167, 171, 173 



Nitrogen, 166, 167, 170 



Noah, 40, 41 



Non-metals, 172 



North Pole: of earth, 10, 16; of magnet, 



200 

 Nutcracker, 343 



Obsidian, 64, 66, 67 



Octaves, law of, 168 



Oersted, Hans, 207 



Oersted's law, 207 



Ohm, 227 



Oil, 73, 76; consumption of, 76; supply 

 of, 76 



Oil gauge, 198 



Oil shale, 73 



Olivine, 50, 58, 59, 62; characteristics 

 of, 59 



Onyx, 54 



Opal, 54 



Opera glasses, 302 



Orchestra, homemade, 325 



Ores, 50 



Ores, iron, 50, 159 



Organ, 325; pipes, 332 



Orion, 1 8, 31, 33, 34 



Orthoclase, 50, 56, 57, 65; characteris- 

 tics of, 57 



Osage orange, 134 



Oscillion, 270 



Overtones, 335 



Oxidation, 149, 176 



Oxygen, 45, 47, 149, 164, 166, 167, 170; 

 discovery of, 150; generation of, 149; 

 molecules of, 164; properties of, 149 



Pan's Pipes, 333 

 Paper, print, 320, 323 

 Papin, Denis, 178 



Peat, 73 



Pegasus, 25, 27, 39, 40 



Penaud's toy bird, 90 



Percolator, 247, 249 



Percussion cap, 140 



Peregrinus, 200 



Periodic law, 168, 170 



Peridotite, 66, 70 



Perseus, 24, 25, 27 



Phaethon, 28 



Phillips, Horatio, 91 



Phlogiston, 150 



Phoebe, n 



Phonograph, 336 



Phosphorus, 167, 170 



Photographic plate, 3, 310, 311, 315 



Physical change, 176 



Piano, tuning of, 333, 334 



Picture, taking the, 313 



Pig iron, 160 



Pitch, musical, 332, 335; of a screw, 349 



Plagioclase, 57, 65; characteristics of, 57 



Plane, inclined, 348 



Planetoid, 2 



Planet, 2, 7, 13 



Planets, orbits of, 8, 9; sizes of, 7 



Planisphere, facing 356 and 357 



Plate: holder, 310, 316; photographic, 



311, 315; sensitivity of, 313, 324 

 Pleiades, 30, 31, 33, 35 

 Pliotron, 270 



Pointers, pole star, 19, 20, 22, 24 

 Pole, North, 10, 16; star, 16, 20, 22 

 Polignac, Cardinal, 151 

 Pollux, 34, 35 

 Polonium, 173 

 Porphyry, 65 

 Potter, Humphrey, 101 

 Powder, 138, 139 

 Power arm, 341 

 Power plants, 125, 126 

 Pressure, electric, 225, 227 

 Pressure of air, in, 112 

 Pressure of water, 113, 124, 125 

 Priestly, Joseph, 150 

 Print, photographic, 321, 322 

 Print paper, 320, 323 



