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In the 17th century, the French scientist Pierre Gassendi knewthat light traveled faster than sound.
在17世纪时，法国科学家皮埃尔伽桑狄已经知道光速要比声速快。
When a gun fired far away, he could see the flash of gunshotlong before he heard the report.
远处发生枪击时，他看到枪的火花的时间远早于才听到枪响的时间。
Gassendi tried to measure the speed of sound by clocking the time that elapsed between the flashand the gunshot.
伽桑狄试图通过记录看到枪的火花和听到枪声之间的时差来测量声速。
Knowing the exact distance the gun was from him, he calculated that soundtraveled through air at over 1,000 miles per hour.
在知道枪支与自己所在位置的精确距离后，他计算出声音在空气中的传播速度约为1000英里/每小时。
This figure is too high, though. Can you guesswhy?
可是，这一数字过高。你能猜出为什么吗？
The problem was that Gassendi relied on his own reaction time,
问题就在于伽桑狄依赖了自己的反应时间，
making his measurement higherthan it should have been.
使得他的测量值高于实际值。
In 1864, another French scientist, Henri Regnault, devised a way to measure the speed of sound automatically, again by using a gun,
1864年，另一位法国科学家亨利?勒尼奥发明了一种自动测量声速的方法，他还是用枪来测量，
but without relying on human reaction time.
但是这次并没有依靠人的反应时间。
Regnault covered a rotating cylinder with paper, and positioned a pen to draw a line as it turned.
勒尼奥用白纸环绕过一个旋 转圆筒，并在上面放置一只笔来在纸上画线记录。
Next, hewired the pen to two electrical circuits, placing one in front of the gun some distance away,
然后，他通过电线将笔接入两条电路中，一条电路放在枪口前的远处某一点上，
and the second near the cylinder, threaded through a diaphragm sensitive to sound.
另一条放在圆筒附近，使之穿过声敏膜片。
When the gun fired, the first circuit broke, making the pen jump to a new position on the rotating cylinder.
枪响后，第一条电路断开，笔尖会跳到旋转圆筒的另外一个新位置上。
When the sound reached the diaphragm by the cylinder, the pen jumped back to itsoriginal position.
当声音触发声敏膜片后，笔会跳回原位。
Because Regnault knew how far the gun was from the cylinder and how fast the cylinder turned,
由于勒尼奥知道枪与圆筒的距离以及圆筒转动的速度，
he calculated that sound travels through air at 750 miles per hour,
于是他计算出声音在空气中的传播速度为750英里每小时，
quite close to the speed physicists accept today.
与今天物理学家普遍认同的声速十分接近。
