From Wikipedia
About 500 years ago, Leonardo Da Vinci (1452-1519) recorded ideas about vortices based on his experiments with water. In fact, the subject of water, hydrology, and hydraulics made up a large part of Leonardo's lifetime study. As a matter of historic note – more of Da Vinci’s writings were devoted to the subject of water than any other subject. The existence of water and its vortices intrigued Da Vinci, prompting him to speculate about the existence and behavior of vortices in the air and cosmos. The power and meaning of vortices in water also led him to closely study the behavior of water under different conditions.
Da Vinci’s fascination with fluid dynamics and vortices crossed over into his art – with the flowing motions of water and vortices being expressed in his paintings and sculptures.
The existence and behavior of bubbles in water was also of interest to Da Vinci, since he noted from close observation that bubbles rise through water in a spiral motion. In his written notes in the Codex Leicester Folio 23V (now owned by Bill Gates), he observed that the "motions of waters always move in a circle from surface to bottom.”
Da Vinci spent many years in his makeshift laboratory and in the field observing the movements of water and air. To see the fluid dynamics of water at work, he did experiments using glass tanks so he could watch the motion of flowing water under various scenarios. During his field research, he maintained detailed notes and drawings to record his experiences and observations.
To facilitate his research, he invented a water gate that utilized the pressure of water to create a tight seal. Unforseen by DaVinci at the time – his experiments and detailed technical drawings of this water gate would survive through time and eventually be used in designing the lock gate system of the Panama Canal.
At times, Da Vinci's mind would ponder the many realms of water as his observations often triggered writing ideas. As a habit, he would jot down or sketch these thoughts along the margins of his papers while working on other subjects.