To measure how many times the diameter of the sun will go into its course in 24 hours.

Make a circle and place it to face the south, after the manner of a
sundial, and place a rod in the middle in such a way as that its
length points to the centre of this circle, and mark the shadow cast
in the sunshine by this rod on the circumference of the circle, and
this shadow will be—let us say— as broad as from *a* to *n*. Now
measure how many times this shadow will go into this circumference
of a circle, and that will give you the number of times that the
solar body will go into its orbit in 24 hours. Thus you may see
whether Epicurus was [right in] saying that the sun was only as
large as it looked; for, as the apparent diameter of the sun is
about a foot, and as that sun would go a thousand times into the
length of its course in 24 hours, it would have gone a thousand
feet, that is 300 braccia, which is the sixth of a mile. Whence it
would follow that the course of the sun during the day would be the
sixth part of a mile and that this venerable snail, the sun will
have travelled 25 braccia an hour.

Taken from
*The Notebooks of Leonardo da Vinci*
edited by Jean Paul Richter, 1880.

. . .

863,

How to prove that the earth is a planet.

865,

866,

The principles of astronomical perspective.

868,

869,

870,

871,

872,

On the luminosity of the Earth in the universal space.

874,

875,

876,

877,

The question of the true and of the apparent size of the sun.

879,

880,

881,

882,

883,

Of the nature of Sunlight.

Considerations as to the size of the sun.

886,

887,

888,

889,

890,

On the luminousity of the moon.

892,

893,

894,

895,

896,

897,

898,

899,

900,

Explanation of the lumen cinereum in the moon.

On the spots in the moon.

. . .