Only a partial answer has been given to the question, "What has Keely done for science?" But enough has been said to convey some idea of the subtle nature of the force he is dealing with, and of the cause of the delays which have again and again disappointed the inventor, as well as the too sanguine hopes of immediate commercial success which have animated the officers and stockholders of "The Keely Motor Company." Keely has no secret to wrest from him. Instead of "Keely's Secret," it should be called "Nature's Secret;" for the problem has still to be worked out, the solution of which will make it "Keely's Secret;" and until this problem is fully solved to the inventor's satisfaction for commercial application, Keely has no secret that he is not willing to disclose, as far as it is in his power to do so. CHAPTER XII. 1891. VIBRATORY PHYSICS.--TRUE SCIENCE. We seem to be approaching a theory as to the construction of ether. Hertz has produced vibrations, vibrating more than one hundred million times per second. He made use of the principle of resonance. You all understand how, by a succession of well-timed small impulses, a large vibration may be set up.--Prof. Fitzgerald. Dr. Schimmel, in his lecture on "The Unity of Nature's Forces," says:--"The Greek philosophers, Leucippus, Anaxagoras, Democritus, and Aristotle, base their philosophies on the existence of an ether and atoms." According to Spiller's system, "both ether and atoms are material. The atoms are indivisible. Chemistry, being based on the correctness of this statement, forces us to accept it." But we are not forced to accept it if it is proved to be false.