The work of the late Sir Charles Wheatstone was very varied in character, and was not limited to one, or even two, of the branches of physics. He investigated the laws of sound, of ordinary and polarised light, and he greatly advanced our knowledge of electricity and magnetism. But there is one characteristic, at least, which runs through all his investigations: he always sought to embody the results of his study of the laws of nature in a practical form, so that they might be beneficial to mankind. Thus he made use of the polarisation of the light of the sky to determine the correct solar time by means of his solar clocks; and again, in his electric instruments, he has enabled us to make electric measurements, and also to interchange ideas with our fellow-creatures all over the globe.