He loved to speculate, too, on Matter and Force, on the nature of atoms and of imponderable agents. "It is these things," says the great German physicist Professor Helmholz, "that Faraday, in his mature works, ever seeks to purify more and more from everything that is theoretical, and is not the direct and simple expression of the fact. For instance, he contended against the action of forces at a distance, and the adoption of two electrical and two magnetic fluids, as well as all hypotheses contrary to the law of the conservation of force, which he early foresaw, though he misunderstood it in its scientific expression. And it is just in this direction that he exercised the most unmistakeable influence first of all on the English physicists."[26] While, however, Faraday was pre-eminently an experimental philosopher, he was far from being indifferent to the useful applications of science. His own connection with the practical side of the question was threefold: he undertook some laborious investigations of this nature himself; he was frequently called upon, especially by the Trinity House, to give his opinions on the inventions of others; and he was fond of bringing useful inventions before the members of the Royal Institution in his Friday evening discourses. The first of these, on February 3, 1826, was on India-rubber, and was illustrated by an abundance of specimens both in the raw and manufactured states. He traced the history of the substance, from the crude uncoagulated sap to the sheet rubber and waterproof fabrics which Mr. Hancock and Mr. Macintosh had recently succeeded in preparing. In this way also he continued to throw the magic of his genius around Morden's machinery for manufacturing Bramah's locks, Ericsson's caloric engine, Brunel's block machinery at Portsmouth, Petitjean's process for silvering mirrors, the prevention of dry-rot in timber, De la Rue's envelope machinery, artificial rubies, Bonelli's electric silk loom, Barry's mode of ventilating the House of Lords, and many kindred subjects. It may not be amiss to describe the last of his Friday evenings, in which he brought before the public Mr. C. W. Siemens' Regenerative Gas Furnace. The following letter to the inventor will tell the first steps:-- "ROYAL INSTITUTION, _March 22, 1862_. "MY DEAR SIR, "I have just returned from Birmingham--and there saw at Chance's works the application of your furnaces to glass-making. I was very much struck with the whole matter. "As our managers want me to end the F. evenings here after Easter, I have looked about for a thought, for I have none in myself. I think I should like to speak of the effects I saw at Chance's, if you do not object. If you assent, can you help me with any drawings or models, or illustrations either in the way of thoughts or experiments? Do not say much about it out of doors as yet, for my mind is not settled in what way (if you assent) I shall present the subject.