The teeth of wheels and why clocks keep unequal time
Three modes of transmission, a recipe for blue-marked iron, and a word-list (1 Jan 1493)
Dated 1 January 1493, this leaf opens the treatise's discussion of gearing: because a wheel's teeth press on the pinion sometimes at their tip and sometimes at their root, the force acts at varying distances from the centre, so a clock cannot keep perfectly equal time even with perfectly made wheels. Leonardo ranks three means of transmitting motion — teeth (strongest, in clocks), cords (in spinning-wheels), and simple contact (weakest, in silk-twisters) — and notes why a scribe can form a small 'o' without a compass. The left margin carries a workshop recipe for finishing iron so it 'appears painted with blue markings', together with a short list of words beginning 'ass-'.
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The teeth of wheels and unequal clock time
Toothed wheels do not exert one same force in driving their pinions: sometimes the tooth's root presses on the pinion tooth's tip, sometimes its tip on the pinion's root, so the force acts at varying distances from the centre with varying power. For this reason a clock's time will not be of equal motion even if its wheels are made perfectly.
Teeth, cords and contact ranked as transmissions
Of the means used in motions — teeth, cords, and contacts — teeth are the most powerful, cords next, and contact the weakest. Teeth occur in clocks and similar instruments, cords in spinning-wheels and the like, and contact as in the twisters of silk.
Recipe: burnished iron with blue markings
Burnished thin iron plates are heated over coals on the side opposite the burnish until they turn blue, then cooled; a design is painted on in white lead and oil, and after drying the plate is put under vinegar. The blue not protected by the lead is removed, leaving a blued pattern; the white lead is then lifted with soft soap. The same may be done on brass.
A word-list of terms beginning 'ass-'
The upper-left column lists a series of words beginning with 'ass-': assettare, assediare, assegniare, assentito, assurbire, assuefare, assummare, assunto, assiduità, assiso, assiatica, assiderare. It reads as a vocabulary or spelling exercise.