Lord Kelvin was the first to appreciate the importance of Joule's discovery, and it was not long before he placed the whole subject of thermodynamics on a scientific basis. He put his conclusions into these easily understandable words: "During any transformation of energy of one form into energy of another form, there is always a certain amount of energy rendered unavailable for further useful application. No known process in nature is exactly reversible: that is to say, there is no known process by which we can convert a given amount of energy of one form into energy of another form, and then, reversing the process, reconvert the energy of the second form thus obtained into the original quantity of energy of the first form. In fact, during any transformation of energy from one form into another, there is always a certain portion of energy changed into heat in the process of conversion, and the heat thus produced becomes dissipated and diffused by radiation and conduction. Consequently there is a tendency in nature for all the energy in the universe, of whatever kind it be, gradually to assume the form of heat, and having done so to become equally diffused. Now, were all the energy of the universe converted into uniformly diffused heat, it would cease to be available for producing mechanical effort, since, for that purpose, we must have a hot source and a cooler condenser. This gradual degradation of energy is perpetually going on, and, sooner or later, unless there be some restorative power of which we have, at present, no knowledge whatever, the present state of things must come to an end." {112} He revealed the Electrodynamics of Qualities of Metals; the size of atoms, the horse-power of the sun; he determined the rigidity of the earth, the laws of the tides, made far-reaching discoveries in electricity, in vortex motion; it might be said of him that he took the universe for his field. But in a chapter like this one is tempted to dwell too long on high achievements. What attracted one more than the achievements was the man, the kindly, sympathetic man who loved truth not celebrity, and work more than its rewards. He was ever the same, whether one met him in Glasgow, London, at sea, or in America, the same simple, straightforward, kindly character. He retained his mental activity to the end. He died at eighty-four, and seemed only to be departing on another journey in quest of truth and friendship.