August 2, 1906] 



NATURE 



325 



•streams of intrinsic energy from tineir own isolated sub- 

 stance, but arc perpetually, though in infinitesimal pro- 

 portions, changing their elemental nature spontaneously, 

 so as to give rise to other atoms which we recognise as 

 other elements? 



I cannot venture as an expositor into this field. It 

 belongs to that wonderful group of men, the modern 

 physicists, who with an almost weird power of visual 

 imagination combine the great instrument of exact state- 

 ment and mental manipulation called mathematics, and 

 possess an ingenuity and delicacy in appropriate experiment 

 which must fill all who even partially follow their trium- 

 phant handling of nature with reverence and admiration. 

 Such men now or recently among us are Kelvin, Clerk 

 Maxwell, Crookes, Rayleigh, and J. J. Thomson. 



Becquerel showed early in his study of the rays emitted 

 "by radium that some of them could be bent out of their 

 straight path by making them pass between the poles of 

 -a powerful electromagnet. In this way have finally been 

 distinguished three classes of rays given off by radium : 

 (i) the alpha rays, which are only slightly bent, and have 

 little penetrative power ; (2) the heta rays, easily bent in a 

 direction opposite to that in which the alpha rays bend, 

 and of considerable penetrative power ; (3) the gamma 

 rays, which are absolutely unbendable by the strongest 

 magnetic force, and have an extraordinanr' penetrative 

 power, producing a photographic effect through a foot 

 thickness of solid iron. 



The alpha rays are shown to be streams of tiny bodies 

 positively electrified, such as are given off by gas frames 

 and red-hot metals. The particles have about twice the 

 mass of a hydrogen atom, and they fly off with a velocity 

 of 20,000 miles a second ; that is, 40,000 times greater than 

 that of a rifle bullet. The heat produced by radium is 

 ascribed to the impact of these particles of the alpha rays. 



The beta rays are streams of corpuscles similar to those 

 ^iven off by the kathode in a vacuum tube. They are 

 charged with negative electricity and travel at the velocity 

 of 100,000 miles a second. They are far more minute than 

 the alpha particles. Their mass is equal to the one- 

 thousandth of a hydrogen atom. They produce the major 

 part of the photographic and phosphorescent effects of the 

 radium rays. 



The gamma rays are apparently the same, or nearly the 

 same, thing as the X-rays of Rontgen. They are probably 

 not particles at all, but pulses or waves in the ether set 

 up during the ejection of the corpuscles which constitute 

 the beta rays. They produce the same effects in a much 

 smaller degree as do the beta rays, but are more pene- 

 trating. 



The kind of conceptions to which these and like dis- 

 coveries have led the modern physicist in regard to the 

 character of that supposed unbreakable bod)' — the chemical 

 atom — the simple and unaffected friend of our youth — are 

 truly astounding. But I would have you notice that they 

 are not destructive of our previous conceptions, but rather 

 elaborations and developments of the simpler views, intro- 

 ducing the notion of structure and mechanism, agitated and 

 whirling with tremendous force, into what we formerly 

 conceived of as homogeneous or simply built-up particles, 

 the earlier conception being not so much a positive asser- 

 tion of simplicity as a non-committal expectant formula 

 awaiting the progress of knowledge and the revelations 

 which are now in our hands. 



As I have already said, the attempt to show in detail 

 how the marvellous properties of radium and radio-activity 

 in general are thus capable of a pictorial or structural 

 representation is beyond the limits both of my powers and 

 the time allowed me ; but the fact that such speculations 

 furnish a scheme into which the observed phenomena can 

 be fitted is what we may take on the authority of the 

 physicists and chemists of our day. 



Intimately connected with all the work which has been 

 done in the past twenty-five years in the nature and possible 

 transformations of atoms is the great series of investi- 

 gations and speculations on astral chemistry and the de- 

 velopment of the chemical elements which we owe to the 

 unremitting labour during this period of Sir Norman 

 Lockyer. 



IFji-e/ess Telegraphy. — Of great importance has been the 



NO. 1918, VOL, 74] 



whole progress in the theory and practical handling of 

 electrical phenomena of late years. The discovery of the 

 Hertzian waves and their application to wireless telegraphy 

 is a feature of this period, though I may remind some of 

 those who have been impressed by these discoveries that 

 the mere fact of electrical action at a distance is that which 

 hundreds of years ago gave to electricity its name. The 

 power which we have gained of making an inslriiment 

 oscillate in accordance with a predetermined code of signal- 

 ling, although detached and a thousand miles distant, does 

 not really lend any new support to the notion that the old- 

 lime beliefs of thought-transference and second sight are 

 more than illusions based on incomplete observation and 

 imperfect reasoning. For the important factors in such 

 human intercourse — namely, a signalling-instrument and a 

 code of signals — have not been discovered, as yet, in the 

 structure of the human body, and have to be consciously 

 devised and manufactured by man in the only examples of 

 thought-transference over long distances at present dis- 

 covered or laid bare to experiment and observation. 



High and Low Temperatures. — The past quarter of a 

 century has witnessed a great development and application 

 of the methods of producing both very low and very high 

 teinperatures. Sir James Dewar, by improved apparatus, 

 has produced liquid hydrogen and a fall of temperature prob- 

 ably reaching to the absolute zero. A number of applica- 

 tions of extremely low temperatures to research in various 

 directions has been rendered possible by the facility with 

 which they may now be produced. Similarly high tem- 

 peratures have been employed in continuation of the earlier 

 work of Deville, and others by Moissan, the distinguished 

 French chemist. 



Progress in Chemistry. — In chemistry generally the 

 theoretical tendency guiding a great deal of work has been 

 the completion and verification of the " periodic law " of 

 Mendel^eff ; and, on the other hand, the search by physical 

 agents such as light and electricity for evidence as to the 

 arrangement of atoms in the molecules of the most diverse 

 chemical compounds. The study of " valency " and its 

 outcome, stereochemistry, have been the special lines in 

 which chemistry has advanced. As a matter of course 

 hundreds, if not thousands, of new chemical bodies have 

 been produced in the laboratory of greater or less theo- 

 retical interest. The discovery of the greatest practical and 

 industrial importance in this connection is the production 

 of indigo by synthetical processes, first by laboratory and 

 then by factory methods, so as to compete successfully with 

 the natural product. Von Baeyer and Heumann are the 

 names associated with this remarkable achievement, which 

 has necessarily dislocated a large industry which derived 

 its raw material from British India. ' 



Astronomy. — A biologist may well refuse to offer any 

 rem.arks on his own authority in regard to this earliest and 

 grandest of all the sciences. I will therefore at once 

 say that my friend the Savilian Professor of Astronomy in 

 Oxford has turned my thoughts in the right direction in 

 regard to this subject. There is no doubt that there has 

 been an immense " revival " in astronomy since 1881 ; it 

 has developed in every direction. The invention of the 

 " dry plate," which has made it possible to apply photo- 

 graphy freely in all astronomical work, is the chief cause 

 of its great expansion. Photography was applied to as- 

 tronomical work before 18.S1, but only with difficulty and 

 haltingly. It was the dry-plate which made long exposures 

 possible, and thus enabled astronomers to obtain regular 

 records of faintly luminous objects such as nebulae and 

 star->spectra. Roughly speaking, the number of stars 



1 I had at first intended to give in this address a more detailed and 

 technical statement of the progress of science than I have found possible 

 when actually engaged in its preparation. The limits of time and space 

 render any such survey on thi'i occasion impos-ible, and, moreover, the 

 patience of even the general meeting of the British Association cannot be 

 considered as unlimited. With a view to the preparation of a more detailed 

 review, I had aslced a number of friends and colleagues to send me notes 

 on the progress and tendency in their own par'icular branches of science. 

 They responded with the greatest generosity and unselfishness I must 

 entirely disclaim for them any responsibility for the brief detached stale, 

 inenis made in the address. At the same time I should wi-h to thank them 

 here by name for their most kind and timely help. Th^'y are : Sir William 

 Kamsay, Mr. Soddy, Prof. H. H. Turner, Dr. Marr, Dr. Haddon, 

 Dr. Smith Woodward, Prof. Sherrington. Prof Farmer, Prof. Vines. Dr. 

 D. H.Scott, Prof. Meldola. Dr Macdougal, Prof. Poulton, Mr. C. V. Boyi 

 Major MacMahon, and Mr. Mackinder. 



