時差N小時:聲速測量 Measuring The Speed Of Sound

In the 17th century, the French scientist PierreGassendi knewthat light traveled faster than sound.

在17世紀時，法國科學家皮埃爾伽桑狄已經(jīng)知道光速要比聲速快。

When a gun fired far away, he could see the flash ofgunshotlong before he heard the report.

遠處發(fā)生槍擊時，他看到槍的火花的時間遠早于才聽到槍響的時間。

Gassendi tried to measure the speed of sound byclocking the time that elapsed between the flashandthe gunshot.

伽桑狄試圖通過記錄看到槍的火花和聽到槍聲之間的時差來測量聲速。

Knowing the exact distance the gun was from him, he calculated that soundtraveled throughair at over 1,000 miles per hour.

在知道槍支與自己所在位置的精確距離后，他計算出聲音在空氣中的傳播速度約為1000英里/每小時。

This figure is too high, though. Can you guesswhy?

可是，這一數(shù)字過高。你能猜出為什么嗎?

The problem was that Gassendi relied on his own reaction time,

問題就在于伽桑狄依賴了自己的反應時間，

making his measurement higherthan it should have been.

使得他的測量值高于實際值。

In 1864, another French scientist, Henri Regnault, devised a way to measure the speed ofsound automatically, again by using a gun,

1864年，另一位法國科學家亨利?勒尼奧發(fā)明了一種自動測量聲速的方法，他還是用槍來測量，

but without relying on human reaction time.

但是這次并沒有依靠人的反應時間。

Regnault covered a rotating cylinder with paper, and positioned a pen to draw a line as itturned.

勒尼奧用白紙環(huán)繞過一個旋 轉(zhuǎn)圓筒，并在上面放置一只筆來在紙上畫線記錄。

Next, hewired the pen to two electrical circuits, placing one in front of the gun some distanceaway,

然后，他通過電線將筆接入兩條電路中，一條電路放在槍口前的遠處某一點上，

and the second near the cylinder, threaded through a diaphragm sensitive to sound.

另一條放在圓筒附近，使之穿過聲敏膜片。

When the gun fired, the first circuit broke, making the pen jump to a new position on therotating cylinder.

槍響后，第一條電路斷開，筆尖會跳到旋轉(zhuǎn)圓筒的另外一個新位置上。

When the sound reached the diaphragm by the cylinder, the pen jumped back to itsoriginalposition.

當聲音觸發(fā)聲敏膜片后，筆會跳回原位。

Because Regnault knew how far the gun was from the cylinder and how fast the cylinderturned,

由于勒尼奧知道槍與圓筒的距離以及圓筒轉(zhuǎn)動的速度，

he calculated that sound travels through air at 750 miles per hour,

于是他計算出聲音在空氣中的傳播速度為750英里每小時，

quite close to the speed physicists accept today.

與今天物理學家普遍認同的聲速十分接近。