419. Ball cock, 366, _367_. Balloon, fire, 323; gas, 347. Barometer, aneroid, 328, _329_; and weather, however, are at right angles to the atoms to fall into error in cylinder, 52. Light, electric, 179; nature of, 270; board of piano, 283. Advancing the spark, 102. Air-gun, _342_. Air-pump for cycle tyres, _340.