INDEX. 



ABSORPTION of light, 261 



of heat, 172 



Abutment, what is an, 45 

 Acetic acid, 305 

 Acids of plants, 305 

 Acid, what is an, 303 

 Action and reaction, explained, 28 



illustrations of, 28 

 Adhesion, what is, 12 

 Adult, oxgyen respired by an, per hour, 



209 



Aerolites, general appearance of, 95 



definition of, 94 



velocity of, 95 



weight of, 95. 



Affinity, what is, 193 



Air, always contains moisture, 91 



in motion, 212 



breathed twice unwholesome, 205 

 condensed by cold, 75 

 currents of. in an occupied room, 212 

 exists in all water, 55 

 expanded by heat, 75 



proof of, 75 

 fresh, how much required per hour 



for breathing, 210 

 heated, ascends, 204 



how proved, 205 

 how ascends in chimneys, 215 

 how escapes from the lungs, 72 

 how heated and cooled, 74, 75 

 impenetrable, 68 

 in motion, why feels cool, 153 



spring, why chilly, 138 

 necessary for the production of sound, 



porous. 63 



atmospheric composition of, 63 



weight of, 00 



how proved, 69 

 when rarefied, 70 

 A/Jbumen, in eggs, 308 



Albumen, in meat, 308 

 what is, 308 

 Alcohol, what is, 305 

 tVlkali, what is, 303 

 Angle, definition of, 251 

 Animals, change of color in winter of, 274. 

 ector of arctic, 175 

 distribution of, 142 

 foretell changes in the weather, 



113 



the strongest, 33 

 Apples, unripe, why sour, 303 



when sour and when sweet, 303 

 Aqueducts, principle of construction of, 50 

 Aqua-fortis, what is, 304 

 Architecture, defined, 41 



origin of the varieties of, 41 

 Architrave, 47 

 Arsenic, poisoning by, 309 



what is, 309" 

 Arch, what is, 43 



when invented, 43 

 Ashes, how preserve a fire, 228 

 Atmosphere, amount of carbonic acid gas 



in, 207 

 height of, 70 

 not invisible, 69 

 pressure of, 71 

 what is the, 69 

 Atom, what is, 5 

 Attraction, what is an, 11 

 Aurora borcalis, cause of, 287 

 height of, 288 

 occurs by day aa well as 



by nisrht, 2S9 

 utility of, 2S9 

 what is, 2S7 

 where seen, 287 

 Avoirdupois weight, origin of, 20 



Ball, elastic, why rebounds, 23 



