As more people live closer together, and as they use machines to produce leisure, they find that their leisure, and even their working hours, become spoilt by a by- product of their machines--namely, noise. Noise is nowadays in the news; it has acquired political status, and public opinions are demanding, more and more insistently, that something must be done about it.46) To control noise is to demand much self-discipline (annoyance arises often from lack of common courtesy) a sense of proportion (there is usually a conflict of interest if a noise is to be stopped), the expenditure of money (and it is far more economical to do this early rather than late), and, finally, technical knowledge.Technical difficulties often arise from the subjective-objective nature of the problem. You can define the excessive speed of a motor-car in terms of a pointer reading on a speedometer. But can you define excessive noise in the same way 47) You find that with any existing simple "noise-meter", vehicles which are judged to be equally noisy may show considerable difference on the meter.Though the ideal cure for noise is to stop it at its source, this may in many cases be impossible. The next remedy is to absorb it on the way to the ear.48) Domestic noises may perhaps be controlled by forethought and courtesy, and industrial noises by good planning and technical improvement. But if we are going to allow fast motor-cycles and heavy diesel lorries to pass continuously through residential and business districts, the community must decide on the control it needs to exercise, for in the long run it has got to pay for it. 49) And if a nation is to take part in modern air trans port, it must enter into international agreements on the noise control measures it will impose at its airports-and here the cost of any real control is to be measured in millions of dollars. Jet engines may be modified to reduce their noise level, or insulation from air traffic noise may be provided by the purchase of land around airports or the insulation of buildings. 50) One estimate is that ＄5.7 billion would be required to equip all existing jet engines with noise control devices; however,, considering the current state of the art, even taking this step will not reduce noise levels at all points to acceptable values. Some combination of methods is probably necessary. To control noise is to demand much self-discipline (annoyance arises often from lack of common courtesy) a sense of proportion (there is usually a conflict of interest if a noise is to be stopped), the expenditure of money (and it is far more economical to do this early rather than late), and, finally, technical knowledge.