What is the instrument Aristotle use to measure earth?

Answer 1

I think you are confusing Aristotle with Eratosthenes, who was the first to attempt to measure the circumference of the Earth -- and did a remarkably good job.

Eratosthenes used a right-angle sundial to measure the angle between our Sun's rays at high noon in his home town of Alexandria, on the day of the summer solstice. He did this because he was told our Sun's rays went straight down a deep well in the city of Syene at that time and day. By assuming our Earth is a sphere, measuring the change in angle between our Sun's rays in Alexandria and in Syene, and making a reasonable estimate of the distance between the two cities; Eratosthenes came up with a circumference of "252,000 stadia." There is some dispute on how to convert stadia to kilometers, but the fact is that he got the right order of magnitude despite using crude instruments and quite a few assumptions.

Answer 2

Aristotle used a method involving sticks and shadows to estimate the circumference of the Earth. By measuring the difference in shadow lengths at two different locations and comparing them to the angle of the Sun's rays, he was able to make his calculations.