"Please. You assumed that we knew more than we do, so a little explanation would help."
"All ordinary vibrations—that is, all molecular and material ones, such as light, heat, electricity, radio, and the like—were arbitrarily called waves of the first order; in order to distinguish them from waves of the second order, which are given off by particles of the second order, which you know as protons and electrons, in their combination to form atoms. Your scientist Millikan discovered these rays for you, and in your language they are known as Millikan, or Cosmic, rays.
"Some time later, when sub-electrons were identified the rays given off by their combination into electrons, or by the disruption of electrons, were called rays of the third order. These rays are most interesting and most useful; in fact, they do all our mechanical work. They as a class are called protelectricity, and bear the same relation to ordinary electricity that electricity does to torque—both are pure energy, and they are inter-convertible. Unlike electricity, however, it may be converted into many different forms by fields of force, in a way comparable to that in which white light is resolved into colors by a prism—or rather, more like the way alternating current is changed to direct current by a motor-generator set, with attendant changes in properties. There is a complete spectrum of more than five hundred factors, each as different from the others as red is different from green.
"Continuing farther, particles of the fourth order give rays of the fourth order; those of the fifth, rays of the fifth order. Fourth-order rays have been investigated quite thoroughly, but only mathematically and theoretically, as they are of excessively short wave-length and are capable of being generated only by the breaking down of matter itself into the corresponding particles. However, it has been shown that they are quite similar to protelectricity in their general behavior. Thus, the power that propels your space-vessel, your attractors, your repellers, your object-compass, your zone of force—all these things are simply a few of the many hundreds of wave-bands of the fourth order, all of which you doubtless would have worked out for yourselves in time. Very little is known, even in theory, of the rays of the fifth order, although they have been shown to exist."
"For a man having no knowledge, you seem to know a lot about rays. How about the fifth order—is that as far as they go?"
"My knowledge is slight and very general; only such as I must have in order to understand my own subject. The fifth order certainly is not the end—it is probably scarcely a beginning. We think now that the orders extend to infinite smallness, just as the galaxies are grouped into larger aggregations, which are probably in their turn only tiny units in a scheme infinitely large.
"Over six thousand years ago the last third order rays were worked out; and certain peculiarities in their behavior led the then Rovol to suspect the existence of the fourth order. Successive generations of the Rovol proved their existence, determined the conditions of their liberation, and found that this metal of power was the only catalyst able to decompose matter and thus liberate the rays. This metal, which was called Rovolon after the Rovol, was first described upon theoretical grounds and later was found, by spectroscopy, in certain stars, notably in one star only eight light-years away, but not even the most infinitesimal trace of it exists in our entire solar system. Since these discoveries, the many Rovol have been perfecting the theory of the fourth order, beginning that of the fifth, and waiting for your coming. The present Rovol, like myself and many others whose work is almost at a standstill, is waiting with all-consuming interest to greet you, as soon as the Skylark can be landed upon our planet."
"Neither your rocket-ships nor your projections could get you any Rovolon?"
"No. Every hundred years or so someone develops a new type of rocket that he thinks may stand a slight chance of making the journey, but not one of these venturesome youths has as yet returned. Either that sun has no planets or else the rocket-ships have failed. Our projections are useless, as they can be driven only a very short distance upon our present carrier wave. With a carrier of the fifth order we could drive a projection to any point in the galaxy, since its velocity would be millions of times that of light and the power necessary reduced accordingly—but as I have said before, such waves cannot be generated without metal Rovolon."