Silk-Doubling Machine and a Perspective Instrument
Two fragments: a device to twist silk thread, and the 'eye' and picture plane
Two recto fragments of technical studies. On sheet 103a Leonardo details a machine to double and twist silk thread: because one worker tends many spindles, the spool unwinding a thread must stop the instant that thread breaks, so the surviving thread does not wind on alone; a spindle S is arranged to halt and to rise only on the circle beneath it. Pulleys with weights, a balance and a short sum (97 + 13 = 110) fill the lower sheet. On sheet 103b a perspective instrument names the 'eye' and the 'wall' (picture plane) where rays to the eye are cut, offered as a way to measure any distance or height.
On this page
Machine to double and twist silk thread
A device doubles and gathers silk so that one worker can tend many spindles. If one of two threads twisted together breaks, the spool that unwinds it must stop at once, so the surviving thread does not wind on by itself. The labelled spools f and l carry the single threads.
Spindle S that halts and lifts
Here the spindle is turned backward and immediately stops its turning. Its raising and lowering come only from the circle S that supports it below, while everything else stays fixed at its height.
Pulley and balance with weights
A pulley is drawn carrying the weights 1 and 3, and a balance scheme is begun below it. They test how a load is carried and weighed across the mechanism.
A short addition
At the right a small sum adds 97 and 13 to give 110. It is working arithmetic jotted beside the mechanical figures.
The 'eye' and the picture plane
On the perspective diagram the line marked a is called 'the eye', and the line marked b the 'wall' or picture plane, where all the rays running to the eye are cut. The span a b is given as 20 braccia.
Instrument to measure distance and height
A note within the apparatus states that it serves to measure any distance or height you wish. A second, analogous figure with the letters a b is drawn lower to the right.