450 



INDEX. 



Repulsion, and attraetion, magnetic, 419 



Retina of the eye, S4S 



Ricocliet firing-, TT 



Rifle, ilini^, construction of, 77 

 how sighted, 7S 



Elvers, why rarely straight, 86 

 velocity of, 15'2 

 water discharge of, 153 



Roads, inclination of, how estimated, 106 

 how should he made, 106 



Rods, discharging, 3S9 



Room, how best ventilated, 264 



Rooms for speaking, how constructed, 201 



£ope-dancing, art of, 52 



8 



Safes, fire-proof, how constructed, 221 

 Sandstones, why ill adapted for architectural 



purposes, l'2ii 

 Saw-dust, utility of in preserving ice, 220 

 Scales, hay and platform described, 98 

 Scarfing and interlocking 117 

 Scissors, a variety of lever, 94 

 Screw, advantage gained by, 109 

 applications of, 109 

 defined, 108 

 endless, 110 

 Hunter's, 110 

 nut of, 108 

 of Archimedes, 159 

 thread of, 109 

 Screw-Propeller, what is a, 155 

 Sea, proximity to, mitigates cold, 263 

 Shadow, what is a, 296 

 Shadows, how increase and diminish, 297 

 Shell, sea, cause of the Bound heard in, 109 

 Ships, copper sheathing of, how protected, 

 416 

 iron, why float, 140 

 Shooting-stars, how accounted for, 290 

 Sliort-sightedness, cause of, 35'2 

 Shot, how manufactured, 30 

 Silver, adulteration of, how detected, 43 

 Simmering, what is, 241 

 Skull, human, combines the principle of the 



arch, 120 

 Smoke, why rises in the air, 43 



why ascends in chimney, 261 

 rings, origin of, 1S7 

 Sneezing, what is, 205 

 Snow crystals, 2S0 



flake, composition of, 2S0 

 how formed, 280 

 line of perpetual, 243 

 protective influence of against cold,220 

 what is, 280 

 Soft, when is a body, 26 

 Solar microscope, 3(58 

 Solid, what is a, 23 

 Solids, why easily lifted in water, 139 



specific gravity, how determined, 39 

 Solution, what is a. 287 



how diflfers from a mixture, 237 

 when saturated, 237 

 Sound, conductors of, 192 



how decreases in intensity, 192 

 how propagated, 190 

 interference of waves of, 194 

 loudness of, on what depends, 194 



Sound, reflection of, 19T 

 velocity of, 193 

 what is, 183 

 when communicated most readily, 



191 

 when inaudible, 190 

 Sounds, musical, 194 



not heard alike by all, 203 

 seem louder by night than by day, 

 191 

 Spark, electric, 388 

 Speaking, rooms suitable for, 201 

 Specific gravity, 37 



how discovered, 44 

 how found, 33 

 standard for estimating, 38 

 practical applications of, 44 

 Spectacles, what are, 360 

 Spectrum, solar, 326 

 Springs, intermitting, 185 



origin of, 136 

 Spy-glass, what is, 364 

 Stability of bodies, depends on what, 48 

 Stairs are inclined planes, 107 

 Stars, shooting, 289 



height of, 289 

 Steel, how tempered, 27 



how magnetized, 421 

 Steel-yard described, 97 

 Steam, advantages of heating by, 265 

 elastic force of, 249 

 superheated, 250 

 high pressure, 250 

 formed at all temperatures, 239 

 guage, 259 



how rendered useful, 252 

 pressure of. how indicated, 260 

 true, invisible. 238 

 when used expansively, 255 

 Steam-boilers, cause of explosion of, 258 

 whistle, 260 

 engine, what is, 251 



condensing. 253 

 construction of, 253 

 high pressure, 2.54 

 regulators of, 255 

 greatest amount of work per- 

 formed by, 251 

 Stethoscope, construction of, 193 

 Still, construction of, 243 

 Structure, influence of the parts on the 



strength of a, 117 

 Stone for architectural purposes, how se- 

 lected, 122 

 Stool, insulating. 380 

 Stove, why snaps when heated, 230 

 Stoves, how differ from open fire-place, 263 

 disadvantages of, 264 

 why placed near the floor, 261 

 Sublimation, what is, 243 

 Sucker, the common, 175 

 Suction, what is, 109 

 Sugar, how refined, 243 



how absorbs water. 145 

 Sun does not really rise and set, 84 

 heat of, why greatest at noon, 210 

 the greatest natural source of heat, 209 

 nature of the surface of, 210 

 Surface defined, 12 



spherical, definition of a, 133 

 Syphon, what is a, 184 



