DISCOVERY 



41 



led to a series of fruitless wars enfeebling still further 

 the already exhausted Greek states. The power which 

 Persia showed in 387 B.C. to dictate the settlement 

 of Greek domestic quarrels corresponds to the real 

 facts of the situation. The Greek world had bled itself 

 to exhaustion. 



There were not wanting minds which felt that the 

 necessity for Hellenism was union in the place of discord. 

 Professor .Murray has pointed out how a revulsion from 

 the experienced horrors of a world war had created 

 dreams of an ideal city where even men have wings. ^ 

 And a more practicable ideal belongs to the same 

 movement of thought. Even during the war, from 

 the pubhcation of the Peace ' onwards, the idea that 

 men should become " good Hellenes " is markedly in 

 Aristophanes' mind. The disintegration resulting 

 from the conclusion of the great conflict loosened local 

 ties, and thereby not only contributed to the marked 

 growth of individualism in the fourth century, but also 

 strengthened the common bond of Hellenism. As 

 a definite political programme, the prototype of the 

 League of N ations finds its spokesman in the Athenian 

 orator Isocrates, who is interesting precisely because 

 he is not a great original thinker, but the mouthpiece 

 of a considerable body of sensible opinion. The dis- 

 cord, jealousy, and rivalry of a narrower patriotism 

 however prevailed. .\ free and voluntary League of 

 Hellenes never came into being. It was left to the 

 Macedonian Philip and his son, .Alexander the Great, 

 to enforce order in the Greek w-orld before conquering 

 Persia and the East. It is to be hoped that the League 

 of Nations wiU be more exactly realised than were the 

 original aspirations of Isocrates, and that the good- 

 will of sensible European opinion will find some really 

 effective expression. If not, it would appear that the 

 parallel between the Greek and European worlds in 

 war-time may be extended to the subsequent periods. 

 To students of the history of Greece in the fourth 

 century this is no attractive prospect. 



' Murray, op. cit., pp. 10, 11. 



- .\ristophanes put his comedy, the Peace, upon the stage 

 in 421 B.C. 



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The Number of the 

 Elements 



By C. G. Darwin, M.G., M.A. 



Fellow 0/ Clirist's College, Cumbridge 



The main endeavour of pure science is to proceed from 

 the study of particular cases to the general laws 

 underlpng them. In this respect it is not very sur- 

 prising to find that chemistry is far behind physics, 

 for chemistry studies the differences between different 

 kinds of matter, whereas physics looks for the uni- 

 fying principles which underlie them all. In fact, it 

 is hardly too much to say that, as soon as any im- 

 portant generahsation is made in chemistry, the subject 

 of it is promoted (or degraded — according to the 

 reader's taste) to the rank of physics. Thus the beau- 

 tiful theory developed by the application of thermo- 

 dynamics to chemistry is dignified with the name 

 Physical Chemistry. The present article deals with 

 another invasion of physics into the chemical domain, 

 an investigation of the fundamental qualities which 

 serve to distinguish between the chemical elements. 



In chemical theory a very important part is played 

 by the " Periodic Law." It would take too long to 

 discuss this law fully, nor is it needed for our purpose. 

 Its main point is this: If all known elements are 

 arranged in order of their atomic weights,^ it is found 

 that certain chemical properties recur at definite 

 intervals. Thus lithium and sodium are both of the 

 group called alkali elements, and are 8 apart, similarly 

 oxygen and sulphur, another pair of closely related 

 elements. For the lower atomic weights the cycle 

 goes by eights, but after two complete cycles it changes 

 and goes by eighteens. In three cases — argon and 

 potassium, cobalt and nickel, tellurium and iodine — 

 it is necessary to invert the order of atomic weights to 

 fit in with the chemical characters. The resemblances 

 of corresponding elements are sometimes not very 

 marked, but they are enough so to prove that there 

 must be some underlying principle, and to enable the 

 chemist to predict the existence of elements through 

 the presence of a gap in the table. Indeed, three of the 

 rarer elements were foretold in this way before their 

 discovery. There still remain two gaps in the table, 

 where there appear to be places for elements that no 

 one has ever found. They ought to be homologous — 

 that is to say, generally similar — to manganese. In the 

 table it will also be seen that there is a curious inter- 



> A good account of the development of the Periodic Law 

 will be found in the Encycl. Brit, under the heading " Elements." 



2 The atomic weight is the weight of an atom of the sub- 

 stance measured on such a scale that the weight of hydrogen is i . 

 In practice, for technical reasons, it is more usual to take that 

 of oxygen as 16, which is almost exactly the same thing. 



