Canadian researcher turns the speed of sound on its ear
Ottawa — ``Henceforth, in science, right is Wong,'' stated the Ottawa Citizen editorial. The play on words referred to the finding by George Wong, a senior research officer of the National Research Council of Canada, that the speed of sound in air is nearly a half mile an hour slower than scientists have reckoned for more than four decades.
Until now, because of an error in calculation, the speed of sound in air was put at 741.5 miles an hour, or 331.45 meters a second.
Dr. Wong's discovery is that sound actually travels at 741.1 miles an hour, or 331.29 meters a second, in dry, ``standard air,'' at 0 degrees Centigrade, and with atmospheric pressure at sea level.
In an interview, Wong acknowledged: ``For normal daily routine, it [his finding] doesn't matter at all.''
For one thing, the speed of sound already varies by many miles an hour according to variations in temperature, humidity, the composition of air, or air pressure. No one is likely to detect such speed changes at echo points or in the lag between seeing a flash of lightning and hearing the accompanying thunder.
As for whether his finding will have some practical impact, Wong says, ``It is hard to say. The engineering ramifications take longer.''
Nonetheless, the idea that such a fundamental constant was inaccurate comes as a surprise to the acousticians, physicists, and aerodynamic engineers that use the number in their calculations.
Probably the small change in the benchmark number won't make any difference in calculating the reverberation times in a concert hall, since these are already imprecise. Nor will it threaten Charles E. Yeager's fame for breaking the sound barrier in an aircraft in 1947, even if that barrier was slightly slower.
Wong was raised in Hong Kong. After getting an engineering degree at the University of Manchester, England, he moved to Canada in 1966.
His finding regarding the speed of sound was a sideline of his work calibrating microphones at the National Research Council in Ottawa. The goal is to maintain standards, to see that 80 decibels as measured in Canada is the same as 80 decibels measured elsewhere.
To make his calibrations more precise, Wong sought a more accurate value for the specific heat of air, that is, the amount of heat needed to raise the temperature by a given amount. His work produced a figure that could in turn be used to calculate the speed of sound. To his amazement, the speed was slower than what the textbooks said.
Wong spent 18 months collecting old scientific papers on the subject. He found they were directly or indirectly based on a 1942 paper by a group headed by H. C. Hardy. Dr. Hardy had gotten his sample of air from a nearby window, dried it, removed the carbon dioxide, and then made his experiment on the speed of sound. In order to make his results apply to standard air, which includes carbon dioxide as well as nitrogen, oxygen, and other gases, Hardy made a mathematical correction to his experimental results.
But, says Wong, Hardy made a mistake. He had also removed some oxygen as well as the carbon dioxide. Wong's finding was published in the May issue of the Journal of the Accoustical Society of America.