"When this concrete part is completed, the inquiry becomes one of... another nature. Knowing that the spaces passed through by the body in each successive second of its fall increase as the series of odd numbers, we have then a problem purely numerical and abstract; to deduce the height from the time, or the time from the height; and this consists in finding that the first of these two quantities... is a known multiple of the second power of the other; from which, finally, we have to calculate..."