There he left

-Spectator.

ALL kinds of matter, say the chemists, whether solid, liquid, or gaseous, are composed of simple substances or elements combined together in an infinite variety of ways. About seventy such elements are known to exist. They combine either in certain fixed and definite proportions by weight represented by relative numbers, or in proportions which are simple multiples of those numbers. These proportional weights are called atomic weights, because, according to Dalton's well-known atomic hypothesis, they are believed to represent the relative weights of the ultimate atoms of the elements. Every element has its own atom with individual properties and an individual weight, and the element is an aggregate of such atoms, each identical with the others. So that if there are seventy elements, there are seventy kinds of atoms, each kind differing from the other kinds in

weight and other properties. When elements combine to form compounds the ultimate particles of the compounds are clusters of elementary atoms, each atom retaining its individuality. Such clusters are called molecules. Thus the molecule, or ultimate particle of water, is a cluster of three atoms, two hydrogen atoms, each weighing one, and one oxygen atom weighing sixteen. The hydrogen atom is the lightest of all, and is taken as unity. We do not know the absolute weight of an atom of oxygen, but we have good reason to believe that it is sixteen times as heavy as an atom of hydrogen, and so for all the other elements. The atomic weights of the elements vary greatly-from hydrogen I to uranium 240-and appear at the first glance to be merely capricious. They are not, indeed, as far as we know exact whole numbers.

So stands the basis of chemistry as

represented in our text-books, and it is not wonderful that such a basis should have been found unsatisfactory by many thoughtful men. The problem is singularly stimulating to those whose restless minds are constantly searching for new revelations. Why are there seventy elements, or thereabouts-why not more or less? Why do their atoms, if they have atoms, show such diversity and apparent eccentricity in weight and disposition? Is Nature limited on its lowest side by these atoms? and, if not, whence did they arise? How, on any possible development hypothesis, can we account for their formation from nebulous matter or for their obvious individuality? Is it not possible that there may have been in reality but one elemental matter from which our cosmical elements have been formed? and inay we not, with the accumulated observations of modern science, hope to obtain some clew to the mystery, some hypothesis not a dream, which shall show us how the evolution may have advanced?

These and similar questions have haunted the minds of chemists since chemistry became a science. Some glimpse of light has from time to time allured us like an ignis fatuus; but no coherent hypothesis was reached, or was indeed possible, until Mr. Crookes, after years of most laborious experimental study and patient thought, found himself, at the last meeting of the British Association, able to suggest one in his address as President of the Chemical Section. Quite recently he has expounded his views anew in a lecture at the Royal Institution, and no one who was present on the latter occasion will forget the eloquence of the lecturer or the brilliance of his experimental illustrations.

It is no easy task to render intelligible to those who are not familiar with chemical theory the great hypothesis which Mr. Crookes has propounded. It is based on no single discovery; and, although its author has contributed much, he lays no claim to the whole of the matter on which it depends. In fact, since Dalton's time material has been slowly collected by a host of work

ers.

Now at last generalization seems possible; and Mr. Crookes has attempt ed it in no spirit of dogmatism, but

with the honest hope of stimulating further study. He asserts nothing, but suggests a great deal.

An

The first consideration in the study is the relationship between the numbers which are believed to represent the relative weights of the ultimate atoms of elements with the properties of those elements. Dumas was the first to point out that the atomic weights of many analogous elements were related to one another in a manner too definite to be accidental. Thus, to take only one case, the atomic weights of the very similar metals, lithium, sodium, and potassium, were respectively 7, 23, and 39, 23 being the exact mean of the other two. This provoked curiosity, but pointed to no law. But in 1863 a much more important step was taken. English chemist, Mr. John Newlands, whose name will be immortal in the history of science, pointed out that, if the elements are arranged in the order of their atomic weights, they are seen to present a uniform sequence of sevens, so that the eighth resembles the first. Thus the eighth from lithium 7 is sodium 23, and the eighth from sodium is potassium 39. So, again, with fluorine, chlorine, bromine, and iodine, and with oxygen, sulphur, selenium, and tellurium, all groups of very similar elements. This "law of octaves" was received with neglect or derision until the researches of Mendeljeff in Russia and Lothar Meyer in Germany showed its supreme importance. Missing links in the chains of octaves were soon observed, and many have already been filled up by researches stimulated by the new law, which was found to be of far deeper significance than its author could have anticipated. The latest expression of it, the immediate precursor and the inducing cause of the Crookes hypothesis, is due to Professor Emerson Reynolds, of Dublin. Unfortunately it is impossible to give an adequate idea of it without a diagram, but some attempt must be made. Imagine a pendulum swinging and slowly coming to rest. Imagine, further, that the pendulum is steadily sinking downward, and, lastly, imagine that a pencil attached to the weight of the pendulum is drawing a line on a vertical sheet of paper behind. On the paper is a perpendicular line

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down the middle. It is evident that the pencil will draw a zigzag line on the paper, right and left of the perpendicular. We shall have, in fact, the pattern which was irreverently described by the wits of the British Association as the O Chemical Corset." Now, if the chemical elements are placed on this zigzag line in the order of their atomic weight with an octave on each line from right to left, and another on each line from left to right, we find that the elements. in similar position on the zigzag lines, in regard to the central perpendicular line, or, in other words, those that are over one another, are similar in properties in a variety of ways. Without going into details, it may be said that those on any part of the zigzag which are approaching the perpendicular are electro-negative, while those receding from it are electro-positive. All the elements on the right of the perpendicular are dia-magnetic, and of uneven valency, while those on the left are paramagnetic (as iron is), and of even valency. If these words convey no idea to our readers, we can only beg them to believe that they represent very definite differences in physical and chemical properties. Many other well-known analogies and divergencies are shown at a glance in the diagram, which is, indeed, as Mr. Crookes describes it, an interesting and even exciting study for chemists. But what has all this chemical theory and this "chemical corset" to do with the genesis of the elements? it may well be asked. We must answer with a most meagre and insufficient sketch of Mr. Crookes's hypothesis, advising all those to whom the exercise of the scientific imagination is a pleasure to study the original. Of course, the whole hypothesis rests on imagination, for no eye can see the events it attempts to depict. But it is no dream, for it rests on a solid basis of observation, and it represents at any rate potential truth. Let it be understood at starting that the pendulum illustration to which further reference must be made, with its right and left swing, and its steady descent, is a symbol typifying two distinct influences, the perpendicular descent a fall of temperature, the lateral swing some exercise of force, possibly, as Mr. Crookes suggests, electricity.

Imagine, then, a universe, or a portion of the universe, without form and void, consisting of nothing but a protyle, to use Mr. Crookes's convenient word, a substance simpler than all elements and prior to them. This condition is antecedent to the formation of suns and planetary bodies which belong to modern history-a mere twenty million years, according to Sir William Thomson. The protyle is at an enormous temperature, which, we presume, means, if heat be motion, in motion of enormous velocity or amplitude. Then begins the cooling, the tendency to equilibrium of temperature, which is the prevalent phenomenon in our cycle of infinite time. As the heat energy of the protyle is lost another energy succeeds it, causing agglomeration of protyle into the small masses, or particles which we call atoms. The first atoms formed are the lightest, the hydrogen atoms. Then in the swing of the cosmic pendulum toward the left, to use the symbol once more, come the positive lithium, glucinum, boron, and carbon atoms, each formed at a definite epoch of the grand development. The pendulum swings back and approaches the perpendicular, and nitrogen, oxygen and fluorine, all negative atoms, are formed at successive stages. The perpendicular line is passed, and the positive sodium, magnesium, aluminium, and silicon atoms are formed in turn, the last forming the apex of the angle and being similar in many respects to carbon, which stands at the first apex. So on until the temperature has fallen so low that the atoms begin to combine with one another, perhaps under the same stimulus of electricity; and in future the agglomeration is not of protyle to protyle, forming atoms, but of atom to atom, forming compounds.

In this manner, or in some manner of which this is symbolical, the elemental forms of matter may have been evolved. Endless questions remain, of course, unsolved; and we cannot expect the writer of such very ancient history to tell us everything. But one paramount question occurs to which Mr. Crookes has devoted the chief labor of many years of his life. Are all the atoms of an element really identical in weight and properties, or is the atomic weight the