時(shí)差N小時(shí):聲速測(cè)量 Measuring The Speed Of Sound

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

在17世紀(jì)時(shí)，法國(guó)科學(xué)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(yuǎn)處發(fā)生槍擊時(shí)，他看到槍的火花的時(shí)間遠(yuǎn)早于才聽(tīng)到槍響的時(shí)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(guò)記錄看到槍的火花和聽(tīng)到槍聲之間的時(shí)差來(lái)測(cè)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(jì)算出聲音在空氣中的傳播速度約為1000英里/每小時(shí)。

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

可是，這一數(shù)字過(guò)高。你能猜出為什么嗎?

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

問(wèn)題就在于伽桑狄依賴了自己的反應(yīng)時(shí)間，

making his measurement higherthan it should have been.

使得他的測(cè)量值高于實(shí)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(guó)科學(xué)家亨利?勒尼奧發(fā)明了一種自動(dòng)測(cè)量聲速的方法，他還是用槍來(lái)測(cè)量，

but without relying on human reaction time.

但是這次并沒(méi)有依靠人的反應(yīng)時(shí)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(guò)一個(gè)旋 轉(zhuǎn)圓筒，并在上面放置一只筆來(lái)在紙上畫(huà)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(guò)電線將筆接入兩條電路中，一條電路放在槍口前的遠(yuǎn)處某一點(diǎn)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(guò)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(kāi)，筆尖會(huì)跳到旋轉(zhuǎn)圓筒的另外一個(gè)新位置上。

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

當(dāng)聲音觸發(fā)聲敏膜片后，筆會(huì)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(dòng)的速度，

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

于是他計(jì)算出聲音在空氣中的傳播速度為750英里每小時(shí)，

quite close to the speed physicists accept today.

與今天物理學(xué)家普遍認(rèn)同的聲速十分接近。