The wind velocity did not exceed 20 km.
The concentration is known, and the conductivity can be measured experimentally; thus the average velocity with which the ions move past each other under the existent electromotive force can be estimated.
When he considered all days irrespective of wind velocity, Mazelle found the influence of temperature obliterated.
After Professor Amund Helfand had, in July 1875, discovered the amazingly great velocity, up to 644 ft.
The second method is in principle extremely simple, consisting merely in multiplying the observed velocity of light by the time which it takes light to travel from the sun to the earth.