In the 17th century, the French scientist Pierre Gassendi knew that light traveled faster than sound. When a gun fired far away, he could see the flash of gunshot long before he heard the report.
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。 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 flash and the gunshot. Knowing the exact distance the gun was from him, he calculated that sound traveled through air at over 1,000 miles per hour. This figure is too high, though. Can you guess why?
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。 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。 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, making his measurement higher than it should have been.
问题就在于伽桑狄依赖了自己的反应时间，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, but without relying on human reaction time. Regnault covered a rotating cylinder with paper, and positioned a pen to draw a line as it turned. Next, he wired the pen to two electrical circuits, placing one in front of the gun some distance away, and the second near the cylinder, threaded through a diaphragm sensitive to sound.
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，但是这次并没有依靠人的反应时间。 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。 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，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. When the sound reached the diaphragm by the cylinder, the pen jumped back to its original position. Because Regnault knew how far the gun was from the cylinder and how fast the cylinder turned, he calculated that sound travels through air at 750 miles per hour, quite close to the speed physicists accept today.
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。 当声音触发声敏膜片后，笔会跳回原位。 由于勒尼奥知道枪与圆筒的距离以及圆筒转动的速度， 于是他计算出声音在空气中的传播速度为750英里每小时，与今天物理学家普遍认同的声速十分接近。
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