Falling bodies, 39-44.

Field, electrical, 328.

magnetic, 308.

Foot, 29.

Foot pound, 74.
Foot poundal, 74.
Force, defined, 47.
electromotive, 356.
lines of, see Lines.
measurement of, 47.
moment of, 57.
Force pump, 183.
Forced vibrations, 207.

Forces, composition of, 52.
graphical representation of, 52.

parallel, 58-60, 82, 83.
resolution of, 56.
Formulas, 524.

Fountain in vacuo, 167.
F. P. S. system, 28.
Franklin, Benjamin, 342.
Fraunhofer lines, 483.
Freezing mixture, 269.
Freezing point, 240, 268.
Friction, 111.

Films, 122.

Flames, musical, sensitive, 233, 234.

Flaming arc lamp, 422.

Flat, in music, 217.

Fleuss pump, 160.
Floating bodies, 148.
Fluid, defined, 11.
Fluorescence, 512.
Fluoroscope, 515.
Focal length, 450, 468.
Foci, of lenses, 467.

of mirrors, 449–455.
Focus, defined, 449.

coefficient of, 111.

electricity produced by, 318, 323,
335.

heat produced by, 247.
Fulcrum, 99.

Fahrenheit scale, 241.

Fall of potential along a conductor, Galvanic cell, 347.

385.

Galvanometer, 380.

and shunt, 390.

deflection of needle in, 365.
Galvanoscope, 380.
Gas engines, 295.
Gases, 11, 157-190.
absorption of, 184.
convection in, 252.
diffusion of, 187.

elasticity of, 158.

Fuse wires for electric circuits, 363.
Fusion, 267.

heat of, 283.

g, determination of, 94.
Galileo, 40, 494.
Galton's whistle, 235.

expansibility of, 157.

expansion of, by heat, 264.

heat conductivity of, 250.
pressure on, 177-180.
sound transmitted by, 195.
weight of, 165.

Gasoline engines, 297.

Maximum current of cells, 360.
Maximum efficiency, 360.

Maxwell, line of force, 308, 366.

Mayer's floating magnets, 304.
Measure of electrical attraction, 320. Northern Lights, 344.
Measurements, 27.

electrical, 380-392.

Nodes, 222.
Noise, 210.

Normal, 444.

North pole, magnetic, 302, 308.

Octave, 214.
Ohm, 354.

Ohm's Law, 357.

Oil surface, effect on water, 122.
Opaque bodies, 435, 478.

Open circuit, 347.

Opera glasses, 494.

Optical center of a lens, 466.
Optical disk, 444.

Optical instruments, 491-501,
Optical lantern, 495.
Oscillation, electrical, 341.

of pendulum, 90.

Oscillator electric fan, 52.

Osmose, Osmotic pressure, 127.
Overtones, 218, 223.

Overturning a body, work done in, 86.

Parabolic curve, 45.

Parallel circuits, 387.

resistance of, 389.

Parallel currents, action of, 393.
Parallel forces, 58-60, 82, 83.
Parallel grouping of cells, 359.
Parallelogram of forces, 54.
Pascal's Law, 130.

Pencil, of light, 436.
Pendulum, 89.

conical, 191.

energy of, 72.

Pendulum method of combining vi-

brations, 229.
Penumbra, 436.

Period, of a pendulum, 91.
Petroleum refining, 276.
Phase of wave, 193.
Phonograph, 234.

Photometry, Photometers, 440.

Physical change, 9.

Physical condition, changes of, 266.

Physics, defined, 13.

Pinhole camera, 438.

Pipe, musical instrument, 225.

Pitch, of screw, 110.

of sound, 210, 212.