The text discusses two main topics: the use of tin oxide (SnO₂) in ancient times and the water-repellent legs of water striders. In the first part, it explains that tin oxide was possibly used as a pigment in ancient times, as it was non-toxic and its use was not recognized for medicinal purposes. It also mentions that lead was becoming recognized as dangerous by the second century AD, which would have made tin oxide a safer alternative. The text references historical sources and scientific studies to support these claims. In the second part, the text describes the water-repellent legs of water striders, which are covered with a hierarchical structure of tiny hairs and nanoscale grooves. This structure enhances the water-repelling properties of the legs, allowing the insects to walk on water. The study uses force-displacement curves and scanning electron microscope images to show the structure of the legs and their water-repelling properties. The research suggests that the water-repelling effect is due to a 'superhydrophobic' effect, where the contact angle with water is greater than 150 degrees. The study also compares the water-repelling properties of the strider's legs with those of a synthetic hydrophobic leg made from a quartz fiber. The findings have implications for the design of miniature aquatic devices and non-wetting materials. The text includes references to various scientific studies and sources.The text discusses two main topics: the use of tin oxide (SnO₂) in ancient times and the water-repellent legs of water striders. In the first part, it explains that tin oxide was possibly used as a pigment in ancient times, as it was non-toxic and its use was not recognized for medicinal purposes. It also mentions that lead was becoming recognized as dangerous by the second century AD, which would have made tin oxide a safer alternative. The text references historical sources and scientific studies to support these claims. In the second part, the text describes the water-repellent legs of water striders, which are covered with a hierarchical structure of tiny hairs and nanoscale grooves. This structure enhances the water-repelling properties of the legs, allowing the insects to walk on water. The study uses force-displacement curves and scanning electron microscope images to show the structure of the legs and their water-repelling properties. The research suggests that the water-repelling effect is due to a 'superhydrophobic' effect, where the contact angle with water is greater than 150 degrees. The study also compares the water-repelling properties of the strider's legs with those of a synthetic hydrophobic leg made from a quartz fiber. The findings have implications for the design of miniature aquatic devices and non-wetting materials. The text includes references to various scientific studies and sources.