THE MIGHTY ATOM.

Auckland Star, Volume LVI, Issue 233, 2 October 1925, Page 9

THE MIGHTY ATOM.

* . RUTHERFORD'S DISCOVERIES. | i FASCIKATIJfG STORY. BY THF. MAN WHO FOUND OUT. An ama'lnc amount nf inter:.-: ia= | shown in the lecture on "The Structure of Atoms."" announced for 'as; night in j the Scots Hall. Upper Symonds Street. | the lecturer being our gaps:. Sir Ernest Rutherford. (. avendish Professor at j < ambridge. who maile the atom give up I its astonishing secret. It mipiit , been the premiere of a popular musical comedy, and many a hara*-?ed ihcatrnnti mflr.aarr would have fel: his heart glow i to ?ep the crowds >urq-,ng into the hall as they did last night. Although by no mean- a small huilriing. tiie hail was . quire inadequate to hold ;h? crowds that wanted to get in. and it is -safe to j say the big Town Hall would not have been too large, had it been available. ! By ten minute- past seven the hall was full upstairs and down, and then the | people began to line up on both side ] wail?, and down the middle aisle. Right | up to eight o'clock optimistic people j kept on arriving, and when they found I themselves unable to get further than j the doors they were a« disappointed as ! though they had paid for seats an.! j misled the performance. It was a wonderful tribute to the reputation of the distinguishc-d scientist we are all so proud to hail a? a fellow New Zealander. j Ar a rule srientiiir matters are not over I popular with the general public, but the pienire^q-; 0 side of the discovery that | the ultimate sped: into which the old bt-hool had resolved matter was really a vast world Ln itself appealed tremendously to people of quite ordinary imagination, coupled to which is Sir Ernest

Rutherford's own amiable and sturdy charaner —and the fact that he belongs to "u-." The chairman for the evening —as the Hon. C-eorge Fowldf*. president pf the University College Council, the lecture being given under the auspices of the Auckland L'niversity College. Old, Yet New. The lecturer. who was listened to with rapt attention by his large audience, some of whom stood right through the evening, explained that, contrary to popular belief, the atomic theory was by no means new. It, could be traced back through history to the Greek civilisation, for some of the philosophers of Greece—not all of them—be- i iieved that matter was composed of I ' atoms, and that their combination and j motion caused all the phenomena of the material world. It was. of course, merely a hypothesis, and had no experimental foundation. The idea again arose in the Renaissance period, but it was not considered in the light of a working hypothesis until Dalton established his theory in ISOC. On Dalton's theory chemists had been able to show that the material universe was composed of 80 or more elemental substances. was not necessary to know. then, what was the nature or size of an atom. There was. at the same time, the certain belief that the atoms of all elements were related in some way to one another. Physicists were interested in seeing if it would be possible to fix the limit either of the maximum or minimum size of an atom. And the first man to really make a guess at it was Thomas Young, the famous professor at the Royal Institution in London. He showed from the phenomena of the ordinary soap bubble that atoms could be reasonably expected to be 100,000,GOOt_ of a centimetre in size. Counting the Atoms. A great change came in 1885, when the structure of atoms was penetrated, and a number of methods of indirectly detecting and enumerating atoms were hit upon. It then became possible to estimate the number of atoms in any given quantity of material. In 1527 an English botanist named Brown, using a fairly powerful micro- j scope, discovered, on looking at a liquid, that the spores in it were perpetually in motion. In ISSO. physicists j took the matter up. and ascertained ; that the irregular motion of these par- j tides could not be attributed to changes | of temperature. The agitation continued apparently indefinitely. With matter in rapid motion, it was possible to detect single atoms. The insistent agitation of small particles had , offered direct proof of the validity of : the kinetic theory of matter. To illustrate the point, the lecturer introduced a film demonstrating the Brownian motion he had referred to. The particles were shown in almost chaotic agitation. Almost Incredible. The real beginning of the modern conception of the atom, said Sir E. Rutherford, was the discovery of two of his own students at Manchester, that the alpha particles (minute quantities of the gas helium) when projected against a sheet of gold, rebounded off the sheet. This discovery was almost incredible, when the terrific energy of the particles was taken into account. The result was compasable to the imagined return of a great shell which had been fired at a sheet of paper. The experiment proved that the alpha par- ] tides must penetrate into the atom and reach such a powerful field that they are bent back. It was from this result that the modern theory of the constitution of matter —the most vital of all the problems of physical science—had been deduced. It was evident from the rebounding action of the particles that they must have encountered an obstacle. Hence was made the assumption that the particles must have hit against something that had mass—a solid entity. From this had been built up the nuclear theory of the atom. At the centre of the atom was a charge system of positive electricity, small in dimensions. The mass of the atom was concentrated at the centre of the nucleus, while electrons (negative electricity ) were distributed about the nudeus to produce the atom's neutrality. This stuTOunding area of electrons might be very extensive. Sow this area was bound to the nucleus, and by what kind of force the integration of the atom was accomplished, it was at the present stage of experimental science, impossible to conjecture. It seemed, though it had not been proved, that the electric charges in the nucleus of the atom varied according to the atomic weight. Gas Collisions. A great contribution to the problem, said the lecturer, had been made by the scientist Moseley, who, in 1913. conducted his famous X-ray experiments. , A relation of extraordinary simplicity obtained between the atoms. The modern idea was that the properties of the atom of a particular element were determined by the charge at the ! nucleus, which, being always; a whole number, resulted in a clear series of the elements being capable of arrange-

I- I- ::.■.._ .■nir-~j-rl I- —_v ment in order. Moseley had been able j to show that ''he properties of an ele- 1 ment depended on this whole nrmber which varied by one in an asc__ding series. By N-ray photographs of any mixture of elements accordingly any element present could b*» detected. The work nf Moselev. combined with the "bombardine"** experiffilents of Marsden,, had gone far To show the actual | value of the nuclear charge in the atom. : Weisht. said Sir Ernest Rutherford, played a very s'lliordinate part in 'ie- ! termining the motion of hodip*. Th. i 1 sijrniticaii:-e of the new a'omir theory | was that it showed the all-importance ! of the nuclear cbarse. Outline of Structure. i The search in physics since ]*!"4 had j culminated in thi* discovery, that the atom really consisted of three sections i—a area if positive electricity. rar.dt up of innumerable electrons; an outer nucleus containing a mixture ot" positive and negative charges. and. finally, an innpr nucleus. ii'nsi-tin_ r of I positive electricity, off which the alpha ; particles rebounded with immense force. ! With the great speeds at which research j student- had been ablp to bombard the j atom with alpha particles it had open i found that the la— of force broke down j owing to the unyielding- character of (this central nuclei-.:-. How this nucleus controls the effective action of the atom I scienc-e had not yet been aide to deter- | mine. I A number of slides, giving statistical i I and diagramatic proof of the methods by which scientists had been able to I measure The mass of art atom ajid the I number of aToms in a given quantity of matter, also aroused the keen interest of the audience. At the close of a most interesting lecture a very hearty vote of thanks was moved by Mr. Kenneth Mackenzie and carried with much enthusiasm, and then the great audience cheered r>ir Ernest lustily.