42. Recording an earthquake
What does a pen have to do to record on paper the vibrations generated by an earthquake?
An earthquake comes like a thief in the night, without warning. It was necessary, therefore, to invent instruments that neither slumbered nor slept. Some devices were quite simple. One, for instance, consisted of rods of various lengths and thicknesses which would stand up on end like ninepins. When a shock came, it shook the rigid table upon which these stood. If it were gentle, only the more unstable rods fell. If it were severe, they all fell. Thus the rods, by falling, and by the direction in which they fell, recorded for the slumbering scientist the strength of a shock that was too weak to waken him, and the direction from which it came.
But instruments far more delicate than that were needed if any really serious advance was to be made. The ideal to be aimed at was to devise an instrument that could record with a pen on paper, the movements of the ground or of the table the quake passed by. While I write my pen moves, but the paper keeps still. With practice, no doubt, I could in time learn to write by holding the pen still while the paper moved. That sounds a silly suggestion, but that was precisely the idea adopted in some of the early instruments (seismometers) for recording earthquake waves. But when table, penholder and paper are all moving, how is it possible to write legibly? The key to a solution of that problem lay in an everyday observation. Why does a person standing in a bus or train tend to fall when a sudden start is made? It is because his feet move on, but his head stays still. A simple experiment will help us a little further. Tie a heavy weight at the end of a long piece of string. With the hand held high in the air, hold the string so that the weight nearly touches the ground. Now move the hand to and fro and around but not up and down. It will be found that the weight moves but slightly or not at all. Imagine a pen attached to the weight in such a way that its point rests upon a piece of paper on the floor. Imagine an earthquake shock shaking the floor, the paper, you and your hand. In the midst of all this movement, the weight and the pen would be still. But as the paper moved from side to side under the pen point, its movement would be recorded in ink upon its surface. It was upon this principle that the first instruments were made, but the paper was wrapped around a drum which rotated slowly. As long as all was still, the pen drew a straight line, but while the drum was being shaken, the line that the pen was drawing wriggled from side to side. The apparatus thus described, however, records only the horizontal component of the wave movement, which is, in fact, much more complicated. If we could actually see the path described by a particle, such as a sand grain in the rock, it would be more like that of a bluebottle buzzing round the room; it would be up and down, to and fro and from side to side. Instruments have been devised and can be so placed that all three elements can be recorded in different graphs.
When the instrument is situated at more than 700 miles from the earthquake center, the graphic record shows three waves arriving one after the other at short intervals. The first records the arrival of longitudinal vibrations. The second marks the arrival of transverse vibrations which travel more slowly and arrive several minutes after the first. These two have travelled through the earth. It was from the study of these that so much was learnt about the interior of the earth. The third, or main wave is the slowest and has travelled round the earth through the surface rocks.
Overprotected children are like the flowers in the greenhouse. They cannot withstand storms.
Good coffee is like friendship, rich and warm and strong.
Maggie is a very diligent person. She works hard like a beaver.
She can’t come to your party this weekend as she is recently as busy as a bee.
She has got a lot of good ideas and I think she is as clever as an owl.
Besides, she has a sweet voice and she can sing like a lark.
I’m always in the mood for forty winks after a good meal.
I’m kind of drowsy.
Then why don’t you go take a catnap?
I’m going to hit the sack.
I’ve got a date with the mattress.
You slept soundly.
He’s a heavy sleeper. An earthquake couldn’t shake him.
unstable share prices
The political situation is highly unstable.
The average stature of the Japanese has increased significantly since the World War II.
Even “fixed” stars like the sun do not really remain stationary.
Stagnant water tends to breed mosquitoes.
The company offers installment plans up to 36 months.
汉语的主动句 = 英语的被动句
It was still thought unusual in some places that programs could be called up by viewers to be displayed on their TV screens at home.
The meeting is scheduled for April 6th.
Water can be changed form a liquid into a solid.
Heat and light can be given off by this chemical change.
Only a small portion of solar energy is now being used by us.
3. 增加主语: 人们， 有人， 大家，我们
What we say here will not be long remembered, but what we do here can change the world.
Measures have been taken to prevent the epidemic from spreading quickly.
fall into a deep slumber
be lost in slumber
disturb sb’s slumbers
slumber away one’s time
a slumberous torpor
rigid in one’s views
rigid adherence to rules
The lion is called the king of animals primarily because of its regal appearance.
The US government tried to topple Saddam Hussein’s regime, but to no avail.
The author earns a 10 percent royalty for every copy sold.
Free-market capitalists do not believe that government should regulate trade.
The sovereignty of Hong Kong was returned to China in 1997.