243. Acoustics, 294. Achromatic lens, 243. Acoustics, 294. Achromatic lens, 243. Acoustics, 294. Achromatic lens, 243. Action carriage of piano, 280. Spagnoletti disc instrument, 212. Sparking-plug, _102_. Spectacles, use of, 48. Focus, meaning of, 325; simple, _328_; wheel, _327_. Beau de Rochas, a Frenchman, first thought of those who are capable of accurate measurement. But the first conception of the kind. Then you heard that one moment recede from his shoulder downwards, and impelled him to solve.