INDEX. 



449 



Mortise, what is a, US 



Mountains, height of, how determined by 



tlie barometer, ITS 

 Movements, vibratory, nature of, 1S3 

 Mud, why flies from wheel of carriage, 79 

 Muscular energy, how excited, SI 

 Music, scale in, 195 



notes in, how indicated, 196 

 Musical sounds, 194 



N 



Natural Philosophy, definition of, 9 

 Near-sightedness, cause of, 352 

 Keedle, magnetic, 423 



dipping, 425 



diurnal variation of, 428 



magnetic, directive power of, how 

 explained, 426 



rariations, cause of, 423 

 Notes, musical, when in unison, 195 

 in music, how indicated, 196 



Ocean, depth of, 123 



extent of, 123 

 Octave in music, 195 

 Oersted's discovery, 429 

 Oils, how diminish friction, 113 

 Opaque bodies, 234 

 Optical instruments, 360 

 Optics, medium in, 312 



science of, 292 



Paddles of a Eteamboat, when most effect- 

 ive, 154 

 Paper, blotting, why absorbs ink, 147 

 Parabola defined, 74 

 Paradox, hydrostatic, 126 

 Pendulum, center of oscillation of a, 59 



compensating, 60 



described, 35 



influence of length on yibration 

 of, 59 



length of a, seconds, Gl 



times of vibration of, 53 



compared, 53 



nsed as a standard for measure, 

 61 

 Perspective, what is, 356 

 Photometers, construction of, 293 

 Physics, definition of, 10 

 Pilaster, what is a, 121 

 Pile, in architecture, 120 



Zamboni's, explained, 404 

 Piles, voltaic, 4iU 

 Pipes, rapidity of water discharged from, 150 



water, requisite strength of, 134 

 Pisa, leaning tower of, 49 

 Pitch, or tone, 195 

 Pkints, viUl action of, 215 

 Platform scales, 93 

 Pliability, what is, 26 

 Plumb-line, 53 

 Pneumatics, 1G3 

 Polarity, magnetic, 419 



I Poles, magnetic, where situated, 426 



of galvanic battery, what are, 402 

 Pop-gun, operation of, 167 

 Pores, defined, 14 



evidence of the existence of, 15 

 Porosity defined, 14 

 Porter, why froths, ISO 

 Portico, what is a, 121 

 Power, agents of in nature, S" 



and resistance defined, C3 



and weight in machinery defined, 93 



expended in work, how ascertained, 



89 

 mechanical effect of, how estimated, 



92 

 moving, effect ot how expressed, 89 

 space and time, how exclianged for, 

 92 

 P^ess, hydrostatic, 127 

 Prism defined, 313 

 Projectile, what is, 74 

 Projectiles, laws of, 74 



range of, 75 

 Propellers, advantage over paddle-wheels, 

 155 

 construction of, 155 

 Pugilists, blows of, when most severe, 69 

 Pulley defined, l'>2 

 kinds of, 102 

 fixed, described, 102 

 movable, 103 

 Pulleys, advantage of, 104 

 Pump, air, 177 



chain, IGO 

 common suction.lSl 



when invented, 160 

 forcing, construction of, 183 

 Vera's, 145 

 Pyrometers, 233 



Quantity in electricity, what is, 403 



R 



Badiation of heat proceeds from all bodies, 



223 

 ruin, what is, 277 



why falls in drops, 277 

 formation of, on what depends, 277 

 guage, 277 



yearly estimated quantity of, 279 

 where most abundant, 273 

 Rain-bow, what is a, 333 



when seen, 335 

 why semicircular, 335 

 Ram, hydraulic, construction and opention 



of, 161, 162 

 Range in gunnery, 75 



greatest, when attained, 75 

 Rays of heat, what meant by, 224 

 Reflection, angle of, 71 

 Reflectors of heat, best, 225 

 Refraction, index of, 316 

 double, 340 



how accounted for, 317 

 Refrigerators, construction of, 221 

 Regulators of steani-engines, 256 

 Repulsion, what is, 22 



