Imagine that the genome (基因组) is a book. The book consists of 23 chapters, with thousands of stories made up of paragraphs, words and letters on different levels. There are one billion words in the book, which makes it longer than 500 dictionaries. If I read the genome out to you at the rate of one word per second for eight hours a day, it would take me a century. If I wrote out the human genome, one letter per millimeter, my text would be as long as the River Danube. This enormous document, however, all fits inside the extremely small nucleus (核) of a tiny cell that fits easily upon the head of a pin (针尖).

The idea of the genome as a book is not, strictly speaking, even a metaphor (比喻). It is true to a great extent. A book is a piece of digital information, written in one-directional form and controlled by a system that translates a small alphabet (字母表) of letters into a large dictionary of meanings through the order of their groupings. So is a genome. The only difference is that all English books read from left to right, while some parts of the genome read from left to right, and some from right to left, though never both at the same time.

While English books are written in words of different lengths using twenty-six letters, genomes are written entirely in three-letter words, using only four letters. And instead of being written on flat pages, they are written on long chains of DNA molecules (分子). The genome is a very clever book, because in the right conditions it can both photocopy itself and read itself.

Noise created by humans, such as car traffic, quieted by about 30% between late March and early May, 2020, when Governor Greg Abbott closed schools and restaurants across Texas, according to analysis by researchers at Southern Methodist University (SMU).

"There was quite a big change in some areas," said Stephen Arrowsmith, a seismologist at SMU, who took on the project with a class of undergraduate and graduate students. Arrowsmith and his students looked at data from a dozen seismometers (地震仪) across North Texas. Seismometers are used to detect earthquakes, but they are sensitive to just about everything that makes the ground vibrate, such as strong winds, ocean waves, construction and traffic.

The idea of using seismometers to track urban noise gained popularity last March when Belgian seismologist Thomas Lecocq posted some of his urban noise data from Brussels on Twitter. Lecocq, of the Royal Observatory of Belgium, received such an enthusiastic response from scientists that he launched the group "Lockdown Seismology" online. "It's where bored seismologists around the world are working together," Arrowsmith joked.

Arrowsmith hopes his findings will contribute to a growing list of creative ways in which researchers are using seismometers. In his course, Arrowsmith teaches students how seismic stations can help investigators solve crimes, like terrorist bombings, aid scientists in tracking nuclear tests or assist inspectors in investigating accidents, like chemical plant explosions. One potential application of his research is to better understand the shallow layers of Earth beneath cities. "That could be useful in places where there's a real seismic hazard (风

险), like San Francisco or Los Angeles," he said, "where just knowing what that shallow structure is tells you a lot about how it would respond in a big earthquake."

It was a sunny winter day. I had gone up and down the tower when, outside the little door at the foot, a blind man came toward me. He was a pale, thin man with dark glasses. He kept close to the inner wall of the courtyard. On reaching the door, he touched it and sharply turned inside. In a moment, he disappeared up the staircase. I stood still, looking at the little sign that said "To the Tower… " I felt obliged to follow. 

I didn't follow closely. I caught up with him in the ticket office. There I was surprised to see the attendant selling him a ticket as though he were any other visitor. With the ticket in one hand and touching the wall with the other, he reached the staircase leading to the hallway. 

"That man is blind," I said to the attendant, but he showed no concern. "He's blind," I repeated. He didn't answer, looking at me vacantly. 

"Perhans he wants to jump," I said. But his chair was too comfortable. He didn't stir. He still looked down at a crossword puzzle he had begun. I turned toward the staircase. 

"The ticket," the attendant said, rising from his chair. It seemed the only thing that could move him. After purchasing my ticket, I hurried up the staircase. 

The man hadn't gone as far as I imagined. After ten minutes, I approached him. "Excuse me," I said as politely as I could, "but I am very curious to know why you came up."

"You'd never guess," he said. 

"Not the view, I take it, or the fresh air on this winter day," I said. 

He smiled. "Coming up the stairs, one can feel the change-the coo staircase suddenly becomes quite warm, —and how up here behind the wall there is shade, but as soon as one goes opposite a narrow window one finds the sun. In all of Siena there is no place so good as here."

He moved into the sunlight. Then he stepped into the shade. "Light, shade, light, shade," he said, and seemed as pleased as a child who, in a game of hopscotch, jumps from square to square. 

We went down the tower together. I left him, gladdened as one can only be by the sunlight.