Experiments on Falling Bodies; Measuring the Sun

Apparatus to time the descent of equal weights

Leonardo describes an upright buried axis m n hinged like a book to a second board o p that can snap shut with two cords. A blowpipe stopped at the foot and filled with pellets of equal weight and shape is fixed above it; when the falling pellets reach the middle of the axis a counterweight is released so the boards close and the pellets stick into the soil, letting him measure the spacing of their descent. He proposes the same method for water, using millet from a hopper weighed braccio by braccio.

Heavy versus light: a pound of lead or of cotton

Two weights double one to the other are compared, and Leonardo asserts the heavier will be less swift than the lighter. He voices the counter-view that a pound of lead falls much more quickly than a pound of cotton.

The warm ox and its cold counterweight

Against the claim that a warm live ox falls more slowly than an equal cold weight because heat makes it lighter, Leonardo objects that if the two were found equal on the balance they must also be equal in descent. Had warmth truly lightened the ox, the scale would already have shown it lighter than its cold counterweight.

Finding the sun's size from a shadow-clock

Given the sun's distance, Leonardo proposes to find its size by timing its motion: set a rod as an ancient sundial, mark the travel of its shadow over one hour, and count how many sun-widths fit that span. Multiplying by 24 hours yields the whole circle; his example of a shadow entering 20 times gives 20 x 24 = 480 suns, from which the diameter of the sun's body follows.

Worked figures: 20 x 24 = 480

A short column of figures works the multiplication behind the solar calculation: 20 shadows times 24 hours giving 480. The digits 24, 20, 480 and 78 are set out one under another at the foot of the sheet.

Margine destro. Figura colle lettere:

Due oggetti, uno rettangolare e uno tondo:

Due oggetti lunghi l'uno il doppio dell'altro:

Due pesi sospesi a carrucola:

Due oggetti, uno largo e l'altro sottile:

Dall'alto lungo il margine sinistro:

Semicerchio con cinque cerchietti nell'arco d'un set- tore:

Operazioni aritmetiche:

Right margin. Figure with the letters:

Two objects, one rectangular and one round:

Two objects, one twice as long as the other:

Two weights suspended from a pulley:

Two objects, one wide and the other thin:

From the top along the left margin:

Semicircle with five little circles in the arc of a sector:

Arithmetical operations: