An inclined rack, a crown-gear, and 'contrary rubbing'
A friction mechanism, with the maxim that every art demands its own instruments
The leaf is filled by a large mechanical drawing — a crown-gear on a horizontal shaft above, and below an inclined toothed rack meshing with a great wheel on a trestle frame, with a small hanging weight at the lower right — captioned only 'A manner of contrary rubbing', making friction between the moving parts its theme. A single line at the head gives a maxim: every body demands its members and every art its instruments, the parts created as soon as the whole is. Beyond these two short captions the mechanism itself is drawn rather than described in the supplied text.
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Inclined rack driving a wheel on a trestle frame
The drawing shows a crown-gear on a horizontal axle above, and below an inclined toothed rack running down to mesh with a large wheel carried on a wooden trestle, a small cylindrical weight hanging at the foot. It is a study of a rack-and-gear transmission, drawn but not described in the given text.
A manner of contrary rubbing
The lower caption, 'A manner of contrary rubbing', names the mechanism's purpose: to demonstrate friction between surfaces moving against each other in opposite senses. It ties the drawn device to Leonardo's study of rubbing and resistance.
Maxim: every art demands its instruments
A line at the head states that every body demands its members and every art demands its instruments, and that as soon as the whole is created its parts too are created. It frames the treatise's concern with mechanisms and the tools proper to each craft.