As instances of such grouping he mentions nickel and cobalt; the two groups of platinum metals; and the so-called “rare earths,” existing in gadolinite, samarskite, &c. Why, then, are these elements so closely associated? What agency has brought them together? It cannot be considered that nickel and cobalt have been deposited in admixture by organic agency; nor yet the groups of iridium, osmium, and platinum; ruthenium, rhodium, and palladium. These features, Mr. Crookes thinks, seem to point to their formation severally from some common material placed in conditions in each case nearly identical. _Argument from the compound radicals._—A strong argument in favour of the compound nature of the elements, Mr. Crookes thinks, is derived from a consideration of their analogy to the compound radicals, or pseudo-elements as they might be called. It may be fairly held that if a body known to be compound is found behaving as an element, this fact lends plausibility to the supposition that the elements are not absolutely simple. From a comparison of the physical properties of inorganic with those of organic compounds, Dr. Carnelley concluded that the elements, as a whole, are analogous to the hydrocarbon radicals. This conclusion, if true, he added, should lead to the further inference that the so-called elements are not truly elementary, but are made up of at least two absolute elements, which he named provisionally A and B. In Dr. Carnelley’s scheme all the chemical elements save hydrogen are supposed to be composed of two simpler elements, A = 12 and B = 2. Of these he regards A as a tetrad identical with carbon, and B as a monad of negative weight; perhaps the ethereal fluid of space. His three primary elements are, therefore, carbon, hydrogen, and the ether. _Argument from polymerisation._—The polymeristic theory of the genesis of the chemical elements propounded by Dr. Mills falls next to be considered. It has been suggested by Dr. E. J. Mills that the pristine matter was once in an intensely heated condition, and that it has reached its present state by a process of free cooling, and that the elements, as we now have them, are the result of successive polymerisations. Chemical substances in cooling naturally increase in density, and we sometimes observe that as the density increases there are critical points corresponding to the formation of new and well-defined substances. The bodies thus formed are known as polymers. From a study of the classification of the elements Mr. Mills is of opinion that the only known polymers of the primitive matter are arsenic, antimony, and perhaps erbium and osmium. _Argument from the Periodic Law._—Lastly a scheme of the origin of the elements, suggested to Mr. Crookes by consideration of Professor Reynolds’s method of illustrating the periodic law of Newlands, is discussed.