3 66 



OUR PHYSICAL WORLD 



Silicon, 47, 167, 170 



Silver, 45 



Simon, the magician, 85 



Sirius, 1 8, 34 



Slag, 1 60 



Slate, 74 



Sling, 131; making, 131 



Squawker, 331 



Squirt gun, 128 



Soapbubble, 109, 116 



Sodium, 167, 169, 170 



Sodium chloride, 168 



Sodium fluoride, 169 



Soil, 46 



Solstices, summer and winter, 1 1 



Sound, intensity of, 335; moves in 



straight line, 326; nature of, 326; 



pitch of, 332, 333; quality of, 330, 



335; rate of propagation, 326, 327; 



reflection of, 327, 328; waves of. 326 

 "Sovereign of the Seas," 118 

 Spar, Iceland, 55 

 Spark gap, 252, 253 

 Spark plug, 192, 193, 195 

 Spearheads, 133 

 Speed boats, 119 

 Sphalerite, 50, 61 

 Spherical aberration, 301, 303 

 Spica, 38 



Spinning wheel, 186 

 Springs, hot, 53 

 Sprocket wheel, 346 

 Stars, i, 17; distance of, 17; magnitude 



of, 1 6, 17; nature of, 17; nearest, 17; 



number of, 16, 17; size of, 18 



Star in the East, 18 

 Starter, electric, 198 

 Steam, pressure of, 186 



Steam engine, effect of on industry, 

 186; governor of, 183, 185; history 

 of, 178; operation of, 184; and 

 schools, 1 88 



Steam injector, 186 

 Steel, 162 



Stephenson, George, 190 

 Stereopticon, 301, 303 

 Stone Age, 158 

 Storage battery, 192 



Stove: early, 151; improvements in, 



iSi 



Stratification, 71, 74 

 Streak, 49 

 Stringfellow, 90 



Strings: vibrating, 325, 328, laws of, 329 

 Sulphur, 45, 47, 51, 167, 170 

 Summer, n 

 Sun, i, 3, 13; corona of, 5; energy of, 3, 



4; size of, 3; source of heat, 4; 



storms on, 5; temperature of, 4 

 Swingback of camera, 314 

 Sympathetic vibrations, 251 



Talc, 50, 58, 60; characteristics of, 60 



Tanks, for developing, 320 



Taurus, 31, 32 



Teeter, 339, 341 



Telegraph, 211, 212; photograph trans- 

 mitted by, 216; signatures trans- 

 mitted by, 216; wireless, 252 



Telegraph Code, 213, 214 



Telegraph of Morse, 212 



Telegraph receiver, 212, 213 



Telegraph sender, 212, 213 



Telegraph of Wheatstone and Cook, 211 



Telephone, 217, 337; construction of, 

 217; Edison's transmitter, 219; inven- 

 tion of, 217; radio, 274; receiver, 218; 

 switchboard, 220, 221; transmitter, 

 218, 219 



Telescope, 300, 302; method of opera- 

 tion, 300 



Temperature and molecular movements, 

 164 



Thermos bottle, 153 



Thunder, 205; storm, 165 



Tides, causes of, 13 



Timer of gas engine, 196 



Top, 133 



Topaz, 50, 51, 54 



Trachyte, 66, 68, 70 



Trade winds, 156 



Transformer, 245, 267 



Transmountain, 22 



Transparencies, 323 



Triangulum, 36 



Triceps muscle, 342 



Tuff, 66, 69 



