Since Roentgen, a German scientist, discovered X-ray in 1895, nondestructive testing has been used as an applied technical discipline for more than one hundred years. However, when we open the chapter of history, brush away the dust of the years, we will be surprised to find that the origin and development of nondestructive testing technology has a rich historical background.

Let's follow the long history, along with the clues of the development of physical science, to find the footprint of the growth of nondestructive testing discipline with a broader vision.

Our country is an ancient civilization in the world and has made a great contribution to the development of science and technology. Our ancient science and technology cultural heritage has many records applying non-destructive testing technology, from which we can see that our ancient time has a simple non-destructive testing science thought.

The physical knowledge of optics, mechanics and acoustics was recorded in Chinese works such as Kao Gong Ji and Mo Jing in pre-Qin period, so that the simple thought of nondestructive testing can be traced back to ancient times. More than 2500 years ago, in the Spring and Autumn period of the State of Qi, there was an important manual industry technology book "Kaogong Ji", which recorded the non-destructive testing method to control the quality of cast copper in the process of copper smelting: "In the form of casting gold, gold (copper) and tin, yellow and white followed; Yellow and white gas exhaustion, green and white second; Green and white gas exhaustion, green gas next, and then can be cast." This text accurately records that when copper is smelted, the smelting process is determined by observing the color of the flue gas, that is, the impurity volatilization in the smelted copper is judged by the different colors of the flue gas during smelting, so as to determine the time for copper water to come out.

This shows that our spring and autumn times have simple applications of non-destructive testing technology, which is similar to today's infrared measurement and control technology. In 400 BC, Mo Di (478 BC -- 392 BC) recorded and discussed the keyhole imaging and the relationship between light color and temperature in the Book of Mo.

During the Spring and Autumn period and the Warring States period, we found that the magnet has the properties of absorbing iron and guide. In the 3rd century BC, the ancient book "Han Feizi" recorded Siman (magnet stone guide phenomenon); "The Spring and Autumn Annals of the Lu Dynasty" recorded "kindness (magnetic) stone summons iron", which is perhaps the earliest record of magnetic attraction. In the 2nd century BC, Liu An (179 BC -- 122 BC) wrote a book called "Zhunanzi", which recorded such phenomena as the repulsion of artificial magnets and magnetic poles.

"On Heng" was written by Wang Chong (AD 2797) in the Eastern Han Dynasty. It records the physical knowledge of mechanics, heat, acoustics, magnetism and other aspects. The content is very rich. Wang Chong in "on balance" there is: "the person so speech appeal, air mouth throat, shake the tongue, a shea mouth, so can become a character. Compared with blowing Xiao Sheng, Xiao Sheng is broken. The more the qi is broken, the more the hand has nothing to do, the more it does not sound. The pipe of the husband's flute is swallowed by a Jew's mouth, and the hand is swallowed by a Jew's mouth." He also said: "One's conduct changes the distance between air and fish, and air should change with water."

It can be seen that he has realized that human voice is generated by air vibration, pointed out that the transmission of vibration should be through the medium, and compared the transmission of sound in the air with the transmission of visible water waves. This analogy is still applicable today when we talk about interference and diffraction of sound waves in ultrasonic testing.

Mengxi Pen Talk was written by Shen Kuo (1031 -- 1195), a statesman and scientist in the middle of the Northern Song Dynasty. It is an important work in the history of Chinese science, recording the discovery of geomagnetic declination, imaging principle of concave mirror and resonance phenomena.