What does "a poetic Qianxun Waterfall, an eternal April day in the world" mean?

It means: The poetry that emerges from the body is as long and flying as the Qianxun Falls. It is the most beautiful April day that has appeared in the world since the beginning of time.

This is an elegiac couplet written by Mr. Jin Yuelin, who had a lifelong love for her, at the memorial service of the modern talented lady Lin Huiyin. The first couplet praises Lin Huiyin's talent, while the second couplet expresses Lin Huiyin's beauty through Lin Huiyin's poem "You Are April in the World", describing Lin Huiyin as the most beautiful April day that has ever appeared in the world. Extended information

Lin Huiyin (June 10, 1904 - April 1, 1955), female, Han nationality, from Min County, Fujian (now Fuzhou), was born in Hangzhou, Zhejiang. His original name was Lin Huiyin, and his name came from "Poetry·Daya·Siqi": The great concubine Huiyin is Bai Sinan. Later, because he was often mistaken for "Lin Weiyin", a male writer at that time, he changed his name to "Huiyin".

The first wife of architect Liang Sicheng, a famous Chinese architect, poet and writer, one of the designers of the Monument to the People's Heroes and the deepening plan of the National Emblem of the People's Republic of China. In literature, he has written essays, poems, novels, scripts, translations and letters, etc. His representative works include "You Are April in the World", "Lotus Lantern", "Ninety-nine Degrees", etc. Among them, "You Are the April Heaven in the World" is the most well-known and widely recited.

Jin Yuelin, philosopher and logician. Graduated from Tsinghua School in 1914, and later studied in the United States, the United Kingdom, and various European countries. After returning to China, he mainly taught at Tsinghua University and Peking University. He never married. I have always been in love with Lin Huiyin.

Lin Huiyin and Liang Sicheng have salon gatherings at their home almost every week, and Jin Yuelin has always been a frequent visitor to the Liang family salon. They have the same cultural background, like-minded interests, and deep friendship. They have been living next to each other for a long time. Jin Yuelin admired Lin Huiyin's character and talent extremely and took great care of him; Lin Huiyin also admired and loved him very much, and the spiritual communication between them was extraordinary. Even when Liang Sicheng and Lin Huiyin had a quarrel, they sought arbitration from the rational and calm Jin Yuelin. Jin Yuelin controlled his emotions with the highest rationality from beginning to end, and loved Lin Huiyin all his life.

In the late 1950s, Lin Huiyin passed away. At the memorial service, he wrote the famous elegiac couplet for her, "A poetic Qianxun Waterfall, an April day in the world forever."

Reference: Baidu Encyclopedia-Lin Huiyin