How the sun heats and lifts the sphere of water, with calculations
Diagrams of the sun round the earth and reckonings that place c nearer the sun than a by the water sphere's radius
The verso continues the recto's cosmology of water. In lettered figures of the sun and the terraqueous globe Leonardo argues that water is heated and raised where the sun strikes it, that a denser substance heats more (earth more than water, water more than air), and that the heated surface of the earth moves at about a thousand miles an hour. A calculation concludes that point c is nearer the 'superficial centre' of the sun than point a by 571 3/7 miles — the semidiameter of the sphere of water — and columns of arithmetic on the sheet work through these figures.
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The sun heats the water sphere; the earth's surface turning ~1000 miles/hour
In lettered propositions Leonardo states that a b c is seen and heated by the sun, its heated boundaries a b moving at about a thousand miles per hour; that the part of the water sphere nearest the sun's 'superficial centre' heats most; and that a denser substance heats more, so water more than air and earth more than water.
Water rises where the sun heats it, and sinks where it does not
'Where it heats less, the water rises less.' On the terraqueous globe, at a and c water is placed by the rivers and taken away by the sun; at d it is placed and raised by the sun; at b it is placed and not lifted. The water that heats most grows most.
Reckoning the water sphere's radius at 571 3/7 miles
Columns of figures on the sheet work out the distances behind the argument, that c is nearer the superficial centre of the sun than a by 571 3/7 miles, the semidiameter of the sphere of water. The operations include the numbers 1142 and 571 tied to that reckoning.