Light and Optics

In 1835 Sir Charles Wheatstone read a paper on the 'Prismatic Analysis of Electric Light' · before the British Association meeting at Dublin. He demonstrated the fact that the spectrum of the electric spark from different metals presented more or less numerous rays of definite refrangibility, producing a series of lines differing in position and colour from each other and that thus the presence of a very minute portion of any given metal might be determined. 'We have here', he said, 'a mode of discriminating metallic bodies more readily than by chemical examination, and which may hereafter be employed for useful purposes'.

This remark is very typical of his farsightedness into the practical utility of any known scientific fact. His 'polar clock' was another instance of this trait of his genius. When Brewster discovered that the plane of polarisation of the light from the sky is always 90 degrees from the sun, Wheatstone devised a clock by which it was possible to tell the hour of the day by the light from the sky though the sun might be invisible.

He also conducted experiments in order to calculate the speed of light and produced a figure of almost 250,000 miles per second - by far the most accurate estimate of that time.