INDEX. 



Abep.batiox, spherical, what is, 329 

 Abutment, what is an, 120 

 Acoustics, 1S3 



Acoustic figures, what are, 1S9 

 Actinism, what is, 343, 3-ti 

 Action and lieaction, 60 



illustrations of, 66 

 laws of, 06 

 Action, voltaic, how interrupted and re- 

 newed, 403 

 Adhesion defined, 29 

 what is, 25 

 Aeriform bodies, liow exert pressure, 174 

 Aerolites, constitution of, 2Sl> 



what are, 283 

 Affinity definel, 25 

 Aim, philosophy of taking, 295 

 Air, compressibility of, 164 



capacity of, for moisture, 268 



constitnents of, 163 



density of, 165 



elasticity of, 165 



fresh, how much required for a healthy 



man, '^Ol 

 heated, why rises, 261 

 how heated, 213 

 in spring, why chilly, 246 

 in water, ISO 

 inertia of, 104 

 momentum of, 1S7 



illustrations of, 187 

 not necessary for the production of 



sound, 101 

 •weight of, 163 

 when rarefied, 166 

 when said to be saturated, 263 

 ■why unwholesome^ after having been 



respired, 260 

 pump, construction of, 176, 177 

 Alphabet, telegraphic, 435 

 Anemometer, 2Si 

 Angle, defined, 71 



of incidence and reflection, 71 

 Animals foretell changes in weather, 202 

 Annealing described, "^7 

 Aqueducts, construction of, 134 

 Arch, base of, 120 



springing of, 120 

 strength of, 120 

 what is an, 120 



why stronger than a horizontal struct- 

 ure, 120 



Archimedes, experiment with the crown, 44 



screw of, 159 

 Architrave, 121 

 Architecture, 119 



orders in, 120 



origin of different styles of, 

 119 

 Armature of a magnet, 423 

 Artillery, effective distance of, 7T 

 Artesian wells, 135 

 Astatic needle, what is an, 430 

 Atmosphere, composition of, 163 



effect of, on diffusion of light, 



302 

 how heated, 226 

 pressure of, 163 

 supposed height of, 173 

 what is, 163 

 Atmospheric electricity, 391 



pressure, effects of, 174, 175 

 how sustained, 179 

 refraction, 314 

 Atom, what is an, 13 



Attraction at insensible distances illustrat- 

 ed, 22 

 cohesive, 25 



liow varies, 25 

 ~ illustration of simple, 13 



molecular, four kinds of, 24 

 mutual, illustrations of, 30 

 wliat is, 17 

 Aurora borcalis, cause of, 396 



no influence on the weather, 291 

 Auroras, not local, 397 



peculLarities vf, 397 

 Avoirdupois weight, 34 

 Axis of a body, what is an, 83 



Balusters, 121 



Balance, ordinary, described, 97 



torsion, 332 



when indicates false weights, 

 Ballast, use of, in vessels, 139 

 Balls, cannon, velocity of, 76 

 Balloons, varieties of. ISO 



what are, 136 

 Balloon, why arises, 43 

 Barker's mill. 157 

 Barometer, how invented, 169-171 

 bow constructed, 171 

 aneroid, 172 



