74 A Line on Kites

Kites are sources of childhood fun. But did you know that not all kites were used as toys?

In 1752 Ben Franklin used a kite to prove that lightning and electricity are the same. He made a flat kite. Then he tied a piece of iron wire to it. This he knew would attract the lightning. Next he used a ball of hemp string. At the end of the string he tied a long silk ribbon. The ribbon would serve as a protective insulator. Between the rose and the ribbon he attached a brass key.

The kite soared into a dark cloud. Soon the rain was coming down the string. It bristled as if it were alive. Franklin knew electricity was striding. He put his finger near the key. A series of sparks jumped from key to finger. He felt the sharp tingle of the sparks. These were really electrical shocks. Franklin’s experiment was dangerous. It took great courage.

Others experimented with kites too. In 1749, two Scotsmen tied a thermometer to a kite. They recorded the temperature of the clouds. Then in 1883, two Englishmen tied a wind meter to a kite. The speed of the wind was measured at 1,200 feet.

The suspension bridge at Niagara Falls was begun by a kite. The kite carried a light line over the gorge. Then the light line drew a heavier one across. Finally, a steel cable was pulled over.

This next event made world history. In 1901, Guglielmo Marconi wanted to prove that a radio signal could be sent across the Atlantic. But first he had to overcome the curve of the earth. He had a brilliant idea. In Newfoundland, he had the receiving antenna raised high in the air on the tail of a kite. The signal came over the Atlantic loud and clear.

风筝是童年乐趣的来源。但你知道并非所有风筝都被当作玩具使用吗？

1752年，本杰明·富兰克林用风筝证明了闪电和电是一样的。他做了一个平板风筝，然后在上面系了一根铁丝，他知道这会吸引闪电。接下来他用了一团麻绳，在绳子的末端系了一条长长的丝绸带，这条丝带用作保护性绝缘体。在麻绳和丝带之间，他系了一把黄铜钥匙。

风筝飞入了乌云中，很快雨水顺着绳子流下来，绳子像活了一样竖起毛来。富兰克林知道电在流动，他把手指靠近钥匙，一连串的火花从钥匙跳到手指上，他感觉到火花的刺痛，这些其实是电击。富兰克林的实验很危险，这需要极大的勇气。

其他人也用风筝做实验。1749年，两位苏格兰人把温度计系在风筝上，记录云层的温度。然后在1883年，两位英国人把风速计系在风筝上，在1200英尺的高度测量了风速。

尼亚加拉大瀑布的悬索桥是由风筝开始建造的。风筝带着一根轻线越过峡谷，然后这根轻线牵引着一根更重的线穿过峡谷，最后一根钢缆被拉了过去。

接下来的事件创造了世界历史。1901年，古列尔莫·马可尼想要证明无线电信号可以跨越大西洋传输，但首先他必须克服地球的曲率。他有一个绝妙的主意，在纽芬兰，他把接收天线高高地架在风筝尾部的空中，信号清晰响亮地从大西洋彼岸传来。