320 



INDEX. 



Persons, why many. ROC the same object Rain, none if the air be dry, 104 



at the same time, 244 

 Perpetual motion in nature, 23 

 instance of, 23 

 Perspiration, insensible, what is, S3 



why caused by active exer- 

 tion, 239 



Pilasters, what are, 45 

 Pile, what is a, 42 



Pipes, lead, how affected by water, 310 

 water, why liable to burst in freez- 

 ing, 1S1 



Pisa, leaning tower of, 17 

 Planets, how give light, 242 

 Plants, how purify the water, 236 



respire as well as animals, 235 

 water, liberate oxygen, 236 

 Platina, the heaviest substance known, 



62 



Plastic bodies, what are, 9 

 Plinth of a column, 46 

 Pneumatics, what is, 49 

 Poison, what is a, 309 

 Poisoning, what to do in cases of, 309 

 Poles of a galvanic battery, 292 

 Pores of a body, 6 

 Portico, what is a, 45 

 Potatoes, frozen, why sweet, 303 

 Potato, starch constitutes the bulk of, 302 

 Posver, how we apply it, 31 

 horse, 33 

 of gunpowder, 34 

 sources of, 32 

 steam, 34 

 water, 33 



Preserves, why turn sour, 306 

 Prism, how separates a ray of light, 255 

 Pump, chain, what is, 100 

 common, 98 



forcing, construction of, 100 

 height to which water may be 



raised by, 99 

 why water rises in, 100 

 Pupil of the eye, 263 



contracts by a sudden 



light, 266 



Putrefaction, causes of, 307 

 Putty, what is, 40 

 Pyrometers, how constructed, 191 



origin of, 91 



water, why called soft, 56 



where most abundant, 103 



why cooler after, 199 



why falls in drops, 91 



yearly amount falling in different 



parts of the earth, IDS 

 Rainbow, formation of, 257 



when seen, 257 

 Rainbows at waterfalls, 253 



double, when seen, 253 



no two persons see the same, 



253 



Rain-gauge, what is a, 109 

 filed rays of light possess the greatest beak 

 ! ing effect, 272 

 'Reflection, line and nnglc of, 246 



of light, 24o 



Reflectors of heat, what arc good, 171 

 RefraagibiUty, 86 

 Refraction of light, 254 

 Remedies for poisons, 309, 310 

 Repulsion, what is, 11 

 Resonance, what is, 125 

 Respiration a form of combustion, 234 

 object of, 234 

 what is, 233 

 Retina of the eye, 263 

 Retort, what is a, 195 

 .Rifle, advantages of, over a musket, 35 

 River, always seems more shallow than it 



is,"255 



bottom, rarely frozen, 181 

 part in which the water runs most 



rapidly, 50 

 Rocks and stones retain moisture, 107 



cause of their rounded and weather- 

 worn appearance, 179 

 why often split in cold weather, 



ISO 



Roman cement, 39 

 Room, air of. how affected by a current 



209 



coolest part of, 117 

 hottest part of, 217 

 Rose, why red, 270 

 SRust, what is, 222 



Salt, how dissolves ice, 1S4 

 Qnadrrfpcd, never raises both feet on a, lakes, origin of, 5S 



side at once, 17 utility of, in the ocean, 58 



Quadrupeds, why swim easier than man,|Sand, best suited for mortar, 39 



63 

 Quick lime, what is, 33 



Radiators, good, of heat, 161 

 Radiation, 160 



of heat, on what depends, 161 

 Rain drops, form of, 169 



why spheres, 160 

 Low measured, 109 



Savages, how hear by placing the ear closo 



with ground, 117 

 Scarfing and interlocking, 43 

 Sea breeze, why cool, 79" 



effect of, on temperature, 107 



rarely freezes, Ib3 



water, why freezes less readily than 

 fresh water, 135 



why not full, 199 



why salt, 47 



vapor of, not salt, 199 

 Seasons, alternation of warm and cold, 112 



