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The figures in the upper line are the atomic numbers, the figures after each element the atomic weights, both in terms of that of hydrogen as unity. Radium, when discovered, fell naturally into the vacant place No. 88, and polonium and actinium are now known to occupy Nos. 84 and 89. The three radioactive emanations of Rutherford, products of radium, actinium and thorium respectively, are chemically analogous to Ramsay's inert family of atmospheric gases, and occupy the place No. 86. No. 91 is known to be occupied by a product of uranium, having a period of average life of only 1 minutes, called Brevium. The numbers 85 and 87 in the above figure now alone remain vacant.

Thus radioactivity has peopled all but two of these vacant places, but it has done more. It has crowded into ten of the above places, between Nos. 81 and 92, no less than 39 distinct elements, and all of the elements occupying any one place-isotopes as they are called-are invariably identical in their whole chemical character. Ionium is isotopic with thorium, mesothorium I. with radium, and so on. To the chemist and the spectroscopist they would be taken as one. Not so, however, to the newer methods of radioactivity.

When the whole sequences of changes of uranium and thorium are set forth in the Periodic Table according to the a- and B-change rules mentioned, it is found that all the final products occupy the place, No. 82, occupied by lead. The atomic weight of the end product of uranium should be 206 and that for thorium 208, whereas the atomic weight of common lead is 207.2. This suggests that common lead is a mixture of isotopes rather than a single homogeneous element. The view rapidly received complete vindication. For the atomic weight of lead derived from minerals rich

in thorium has been found to be higher than that of common lead, whereas the atomic weight of lead derived from minerals rich in uranium is lower. The values in fact vary from 206.0 to 207.7.

The densities of the varieties of the lead, the writer recently found, differ in exactly the same way as the atomic weights, showing that the volume of the atom is the same though the weights are different, as was to be expected from general theoretical considerations. The difference is only small. "Thorium" lead is about per cent. heavier than common lead. Prof. Richards, of Harvard, has since found "uranium" lead to be per cent. lighter than common lead. But if such a difference occurred with gold, a bank-teller would be liable to be out by one sovereign, or two, in every 400, if he weighed the coins instead of counting them.

Gold was the goal of alchemy, and it is interesting to ask whether the new discoveries have thrown any light on the alchemical problem of how to make gold from lead or mercury. The answer may be given at once. Gold is followed in the Periodic Table by mercury, thallium, lead, and bismuth, occupying successive places without gaps, as the figure shows. To get gold from mercury, expel from the atom of mercury one B-particle, which will make thallium, then one a-particle, which will turn the thallium into gold. Or, to get gold from lead, expel from the atom of lead one a-particle, which will turn it into mercury, and proceed as before.

It is interesting to note that, in the case of both the thorium and uranium disintegration series, at a certain stage, the expulsion of an a-particle instead of a B-particle would have resulted in gold being produced, for in each case the place occupied by thallium is entered in the course of the changes.


Unfortunately it is not yet possible to supplement these simple recipes for the artificial production of gold with the necessary instructions as to how an atom is to be caused to expel an a- or a B-particle at will, unless Nature has decreed that it should do so of itself, in which case nothing known will prevent it. But, if man ever achieves this further control over Nature, it is quite certain that the last thing he would want to do would be to turn lead or mercury into gold-for the sake of gold. (The energy that would be liberated, if the control of these sub-atomic processes were as possible as is the control of ordinary chemical changes, such as combustion, would far exceed in importance and value the gold. Rather it would pay to transmute gold into silver or some base metal.

War, unless in the meantime man had found a better use for the gifts of science, would not be the lingering agony it is to-day. Any selected section of the world, or the whole of it if necessary, could be depopulated with a swiftness and dispatch that would leave nothing to be desired.

Indeed in the whole tragic history of the past few years nothing has been perhaps more illuminating than the attitude of the world and its rulers to science. The intellectual aspect of the discoveries here briefly enumerated-the discovery of radioactivity, the realisation that it was due to a natural transmutation of the elements, the laborious tracing out, step by step, of the complicated sequence of changes, the discovery of the law connecting these changes with the Periodic Table, the first real understanding as to what constitutes the difference between one element and another, the vista that opens out should man ever exercise over these higher order of natural energy the control he has so effectively assumed over the lower interesting

perhaps, but what is the use of it all? There is a rumour, puffed judiciously in the press, that radium is a cure for cancer, and immediately there is a change. Stock exchanges get up radium, wild-cat mining schemes are floated, the public are invited to get rich quickly, and every quack and charlatan, with his radium ointment, radium pills, and radium waters, refurbishes his familiar propaganda. The charitable and benevolent, to whom the cry of suffering and the dying ever make its irresistible appeal, raise the funds to buy the radium. The genuine scientific investigator can no longer afford to, and goes without.

Again the scene changes and the country is spending nearly £100 every second on the war. Radium, like every other gift of science, is pressed into the service of the war, as it is convenient for illuminating the dials of watches and scientific instruments at night, and the State, which before as regards anything productive or creative did not exist, must now afford anything for the purpose of destruction. Men, materials, and capital must be conscripted and organised to the last point for the purposes of occasional international strife.

But there is a struggle which is world-wide and never-ending, the struggle against external nature for control and mastery. The millions take no part in it, are hardly aware that it goes on, and would be surprised if they were told that their future fate and prosperity depended upon it rather more intimately than upon the issue of the doughty conflicts of the parliamentarians some of them send up to Westminster. Neither, again, would the mere alteration in the character of their education, making it scientific rather than classical, alone bring them salvation. For this struggle is by duel rather than by armies, and the issue of the duel the millions accept as blindly




and dumbly as a decree of Providence. tracts of the British Empire are uninhabitable by white men by reason of malaria and yellow fever. It is the will of Allah. A solitary duellist1 against the unknown and not understood confronted Nature. A single intelligence in the teeth of official apathy and neglect sought the "million murdering cause," and found it. In India alone more than a million people died yearly from malaria before its cause and remedy were ascertained. The Panama Canal owes its successful construction to the work of this solitary individual in Bangalore, diligently followed up by others. Praise be to Allah!

The future of the British Empire is at the moment in the hands of five million stalwart men, with an organised nation of workers and vast accumulations of wealth and resources and every possible scientific discovery and invention behind to back them up. If the nation thinks, when peace returns, that the struggle against Nature, which after all is of more abiding and permanent interest to its destiny, large as the present contest looms to-day, can be best carried on in the old way by a handful of isolated individuals as a sort of hobby in their spare time, out of their own means, and in the intervals of more urgent professional duties, the nation is mad.

[The war being now over, it is not out of place to add that an even greater danger than neglect awaits the scientific investigator, the danger that he along with every other creative element in the community will be remorselessly shackled and exploited to bolster up the present discredited social system. There is abundant evidence since the war that science rules the world, and he who would aspire to rule it must first rule science. The prospect of creative science under the heel of government depart

1 Sir Ronald Ross.


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