touching personal explanation how with advancing years his memory had failed, and that in justice to others he felt it his duty to retire. At intervals he still attempted to work at research. In 1860 he sent a paper to the Royal Society on the relations of electricity to gravity, but, on the advice of Professor (afterwards Sir George) Stokes, it was withdrawn. He had also in contemplation some experiments upon the time required in the propagation of magnetism, and began the construction of a complicated instrument, which was never finished. [Sidenote: HYPOTHESIS AND EXPERIMENT.] His very last experiment, as recorded in his laboratory notebook, is of extraordinary interest, as showing how his mind was still at work inquiring into the borderland of possible phenomena. It was on March 12th, 1862. He was inquiring into the effect of a magnetic field upon a beam of light, which he was observing with a spectroscope to ascertain whether there was any change produced in the refrangibility of the light. The entry concludes: “Not the slightest effect on the polarised or unpolarised ray was observed.” The experiment is of the highest interest in magneto-optics. The effect for which Faraday looked in vain in 1862 was discovered in 1897 by Zeeman. That Faraday should have _conceived_ the existence of this obscure relation between magnetism and light is a striking illustration of the acuteness of mental vision which he brought to bear. Living and working amongst the appliances of his laboratory, letting his thoughts play freely around the phenomena, incessantly framing hypotheses to account for the facts, and as incessantly testing his hypotheses by the touchstone of experiment, never hesitating to push to their logical conclusion the ideas suggested by experiment, however widely they might seem to lead from the accepted modes of thought, he worked on with a scientific prevision little short of miraculous. His experiments, even those which at the time seemed unsuccessful, in that they yielded no positive result, have proved to be a mine of amazing richness. The volumes of his “Experimental Researches” are a veritable treasure-house of science. CHAPTER VI. MIDDLE AND LATER LIFE. Although to avoid discontinuity the account of Faraday’s researches has in the previous chapter been followed to their close in 1862, we must now return to his middle period of life, when his activities at the Royal Institution were at their zenith. [Sidenote: BREAKDOWN OF HEALTH.] Mention has been made of the serious breakdown of Faraday’s health at the close of 1839. Dr. Latham, whom he consulted as to his attacks of giddiness, wrote to Brande:-- Grosvenor Street, December 1, 1839.