"To-morrow, at 4 o'clock, immediately after Max Müller's lecture, I shall show Sir Henry Holland an apparatus which has arrived from Munich to manifest the phenomena of light which have recently been made known to us by Bunsen and Kirchhoff. Mr. Barlow will be here, and he suggests that you would like to know of the occasion. If you are inclined to see how philosophers work and live, and so are inclined to climb our narrow stairs (for I must show the experiments in my room), we shall be most happy to see you. The experiments will not be beautiful except to the intelligent. "Ever your faithful Servant, "M. FARADAY." Sometimes, too, the exhibition of a scientific fact would take him away from home. Thus, when her Majesty and the Prince Consort once paid a private visit to the Polytechnic, Mr. Pepper arranged a surprise for the Royal party, by getting Faraday in a quiet room to explain the Ruhmkorff's coil--the latest development of his own inductive currents. This he did with his usual vivacity and enthusiasm, and the interview is said to have gratified the philosopher as well as the Queen. He could not, however, escape the inroads made upon his time by correspondence. People would write and ask him questions. Once a solitary prisoner wrote to tell him, "It is indeed in studying the great discoveries which science is indebted to you for, that I render my captivity less sad, and make time flow with rapidity,"--and then he proceeds to ask, "_What is the most simple_ combination to give to a voltaic battery, in order to produce a spark capable of setting fire to powder under water, or under ground? Up to the present I have only seen employed to that purpose piles of thirty to forty pairs constructed on Dr. Wollaston's principles. They are very large and inconvenient for field service. Could not the same effect be produced by two spiral pairs only? and if so, what can be their smallest dimension?" And who was the prisoner who thus speculated on the applications of science to war? It was no other than Prince Louis Napoleon, then immured in the fortress of Ham, and now the ex-Emperor of the French. At another time he wrote asking for his advice in the manufacture of an alloy which should be about as soft as lead, but not so fusible,--a question which also had evident bearing upon the art of war; and offering at the same time to pay the cost of any experiments that might be necessary.