126 



DISCOVERY 



limitations of human power ; they were confessions of 

 human impotence. 



Now since it is kno\^'n that all bodies are composed 

 of atoms — the smallest particles of matter that can 

 take part in a chemical change — it follows, it was 

 argued, that an element must be composed of atoms 

 of one kind only, for if it were composed of two or 

 more kinds, it is very probable that someone, ere now, 

 would have separated one from another, and that 

 would contradict the definition of the word. 



In the old days, then, an element was believed to be 

 an assemblage of atoms each of which had identical 

 properties. The truth revealed by experiment, how- 

 ever, differs from the conclusion of the argument 

 above. We now know that what was called an element 

 may contain atoms of different kinds, but — and this 

 is important— although these kinds differ in a few 

 respects, in most they are so similar that they cannot 

 be separated by any known chemical process. Had 

 this conclusion originated in a man's mind as a bright 

 idea, it would surely have been rejected as making 

 unnecessarily complex something essentially simple. 

 Yet the experiments of workers on radio-activity in 

 the years immediately preceding the war, and of 

 Dr. Aston on positive-rays in the years since, have 

 rendered it extremely probable. 



Let us take an example from Dr. Aston's book. The 

 metallic element magnesium, whose atomic weight is 

 24-32, is found to consist of three bodies having atomic 

 weights of 24, 25, and 26. Each of these, as far as 

 we know, is an assemblage of absolutely similar atoms, 

 and therefore is an element in the old sense. Mag- 

 nesium, on the other liand, although it is known by 

 physical means to be a mixture of the three, cannot 

 be separated by any known chemical process into its 

 constituents. Not being decomposable, it too is an 

 element. 



Which, then, is to be called an element, the 

 embracing whole or the constituent part ? If the 

 three magnesiums be called elements, they must be 

 given distinguishing names and a new name must be 

 invented for their mixture ; also the word " element " 

 would tlien mean something different from what it 

 has meant in the chemical and physical hterature of 

 the past centurj'. The difficult}' is best resolved in 

 this way. It is known that each of the three mag- 

 nesiums gives absolutely the same X-ray spectrum, 

 which is, therefore, that of the composite body. Now 

 the X-ray spectrum is believed to be the most funda- 

 mental property of a chemical element. It is an 

 excellent thing, therefore, on which to base a definition. 

 Ninety-two (but only ninety-two) different X-ray 

 spectra are known to be capable of existing in nature, 

 and eighty-seven of these have actually been found in 

 an examination of bodies. It is simplest, therefore, to 



make the X-ray spectrum the distinguishing criterion 

 of a chemical element and to define an element as a 

 substance possessing a unique X-ray spectrum. On 

 this view there can be but ninety-two different elements 

 of which eighty-seven are known. 



It follows from this that if a substance is shown by 

 the positive-ray method or otherwise to be a mixture 

 of non-separable constituents, the mixture is called an 

 element ; if it is shown to be wholly one constituent, 

 that too is called an element. Each of the constituents 

 of the mixture which comprise the element is called 

 an isotope. An isotope, but not necessarily an 

 element, is consequently an assemblage of absolutely 

 identical atoms. Those elements which are found to 

 be mixtures of isotopes are called " complex " elements, 

 those which cannot be resolved into isotopes, " simple " 

 elements. Remembering that isotopes are non-separ- 

 able, we arrive at the following description of an 

 element : A substance with a tniique X-ray spectrum, 

 which may or may not be a mixture of isotopes, and which 

 cannot be decomposed into anything simpler by any 

 known chemical process. 



The following elements have been found to be 

 simple (I quote from Dr. Aston's book) : hydrogen, 

 helium, beryllium, carbon, nitrogen, oxj'gen, fluorine, 

 sodium, phosphorus, sulphur, arsenic, iodine, and 

 cssium. Of the elements found to be complex, 

 lithium, boron, neon, sihcon, chlorine, argon, potas- 

 sium, nickel, bromine, rubidium, actinium, protacti- 

 nium, uranium, and possibly calcium, consist of two 

 isotopes ; magnesium and possibly silicon of three ; 

 thallium and possibly zinc of four ; xenon of five ; 

 krj'pton and possibly mercury of six. The elements 

 which have not been classified remain still to be 

 investigated. 



A. S. Russell. 



Some Religious Beliefs 



and Survivals in 



Rural Japan 



By the Rev. Walter Weston, M.A., F.R.G.S. 



Late British Chaplain at Yokohama 



Nothing so strongly shows the contrasts between the 

 Japanese townsman and the Japanese peasant as a 

 growing familiarity with the religious ideas and customs 

 of the vast majority of the peasantry and of the 

 dwellers in the remoter regions of the interior. They 

 are a shy folk in these matters, simple-minded, and not 



