**Age 16.** Between 1894 and 1895 Einstein writes an essay and sends it to his uncle Caesar Koch. He believes in the ether. Einstein is also familiar with the principle of relativity in mechanics

A year later, in 1895-1896, while in Aarau, Einstein conceives of a thought experiment: Einstein chases a light beam

In 1899 Einstein studies Maxwell’s electromagnetic theory

Around 1898-1900Einstein invents the magnet and conductor thought experiment

Between 1899 and 1900 Einstein is occupied with the contradiction between the Galilean principle of relativity and the constancy of the velocity of light in Maxwell’s theory

Between 1899 and 1901 Einstein is interested in ether drift experiments, and appears to have designed at least two experiments, the first in 1899

In 1901 Einstein still accepts the Galilean kinematics of space and time, in which the Galileian principle of relativity holds good

In 1902 Einstein reads Hendryk Antoon Lorentz’s 1895 seminal work on electron theory

Between 1901 and 1903 Einstein is working with the Maxwell-Hertz equations for empty space. He tries to find solutions to two problems

Magnet and conductor experiment and Faraday’s induction law lead to a conclusion that there is an asymmetry in the explanation depending on whether the magnet moves or the conductor moves. Einstein analyzed the magnet and conductor thought experiment according to Maxwell’s theory and the Galilean transformations. But covariance of Maxwell equations failed

Einstein confronts a conflict between the principle of Galilean relativity and the constancy of the velocity of light

Between 1901 and 1903 Einstein drops the ether hypothesis and chooses the principle of relativity instead of the postulate of the constancy of the velocity of light, and finds a (temporary) solution for his conflict in the form of an emission theory

Einstein seems to have pondered with this problem for an extra year, from 1903-1904 until almost spring-summer 1904. Einstein discusses Fizeau’s experiment using emission theory. He demonstrates, by using Fizeau’s celebrated experimental result, why this standpoint of emission theories cannot hold true

Towards spring-summer 1904 Einstein dropps emission theory and returns to Lorentz’s theory. He spends almost a year in vain trying to modify the idea of Lorentz in the hope of resolving the above problem. Einstein tries to discuss Fizeau’s experiment in Lorentz’s theory [In 1895 Lorentz managed to derive the Fresnel Formula from the first principles of his theory (stationary ether and moving electrons) without the need of any partial ether drag. Lorentz thus adhered to Fizeau’s original 1851 experimental result, but not to Fresnel’s theoretical interpretation of partial ether drag hypothesis, used to derive his dragging coefficient]. Finally

**Age 26. **In spring 1905, Einstein found the final solution, the “step”, which solved his dilemma

For footnotes, references, and further details please consult my papers