444 



NATURE 



[September 8, 1S98 



of nitrate is clearly within view, and by its aid the land devoted 

 to wheat can be brought up to the thirty bushels per acre 

 standard. In days to come, when the demand may again over- 

 take supply, we may safely leave our successors to grapple with 

 the stupendous food problem. 



And, in the next generation, instead of trusting mainly to 

 food-stuffs which flourish in temperate climates, we probably 

 shall trust more and more to the exuberant food-stuffs of the 

 tropics, where, instead of one yearly sober harvest, jeopardised 

 by any shrinkage of the scanty days of summer weather, or of 

 the few steady inches of rainfall, nature annually supplies heat 

 and water enough to ripen two or three successive crops of food- 

 stuffs in extraordinary abundance. To mention one plant alone, 

 Humboldt — from what precise statistics I know not — computed 

 that, acre for acre, the food-productiveness of the banana is 

 133 times that of wheat ; the unripe banana, before its starch is 

 •converted into sugar, is said to make excellent bread. 



Considerations like these must in the end determine the range 

 and avenues of commerce, perhaps the fate of continents. We 

 must develop and guide nature's latent energies, we must utilise 

 her inmost workshops, we must call into commercial existence 

 Central Africa and Brazil to redress the balance of Odessa and 

 Chicago. 



Having kept you for the last half-hour rigorously chained to 

 earth, disclosing dreary possibilities, it will be a relief to soar to 

 the heights of pure science and to discuss a point or two touch- 

 ing its latest achievements and aspirations. The low temper- 

 ature researches which bring such renown to Prof. Dewar and 

 to his laboratory in the Royal Institution have been crowned 

 during the present year by the conquest of one of nature's most 

 defiant strongholds. On May lo last Prof. Dewar wrote to me 

 these simple but victorious words : " This evening I have suc- 

 ceeded in liquefying both hydrogen and helium. The second 

 stage of low temperature work has begun." Static hydrogen 

 boils at a temperature of 238° C. at ordinary pressure, and at 

 250° C. in a vacuum, thus enabling us to get within 23° C. of 

 .absolute zero. The density of liquid hydrogen is only one- 

 fourteenth that of water, yet in spite of such a low density it 

 collects well, drops easily, and has a well-defined meniscus. 

 With proper isolation it will be as easy to manipulate liquid 

 hydrogen as liquid air. 



The investigation of the properties of bodies brought near the 

 absolute zero of temperature is certain to give results of extra- 

 ordinary importance. Already platinum resistance thermometers 

 are becoming useless, as the temperature of boiling hydrogen 

 is but a few degrees from the point where the resistance of 

 platinum would be practically nothing, or the conductivity 

 infinite. 



Sevejral years ago I pondered on the constitution of matter in 

 what I ventured to call the fourth state. I endeavoured to 

 probe the tormenting mystery of the atom. What is the atom ? 

 Is a single atom in space solid, liquid, or gaseous ? Each of these 

 states involves ideas which can only pertain to vast collections 

 of atoms. Whether, like Newton, we try to visualise an atom 

 as a hard, spherical body, or, with Boscovitch and Faraday, to 

 regard it as a centre of force, or accept the vortex atom theory 

 of Lord Kelvin, an isolated atom is an unknown entity difficult 

 to conceive. The properties of matter — solid, liquid, gaseous — 

 are due to molecules in a state of motion. Therefore, matter as 

 we know it involves essentially a mode of motion ; and the atom 

 itself — intangible, invisible, and inconceivable — is its material 

 basis, and may, indeed, be styled the only true matter. The space 

 involved in the motions of atoms has no more pretension to be 

 called matter than the sphere of influence of a body of riflemen 

 — the sphere filled with flying leaden missiles — has to be called 

 lead. Since what we call matter essentially involves a mode of 

 motion, and since at the temperature of absolute zero all atomic 

 motions would stop, it follows that matter as we know it would 

 at that paralysing temperature probably entirely change its 

 properties. Although a discussion of the ultimate absolute 

 properties of matter is purely speculative, it can hardly be 

 barren, considering that in our laboratories we are now within 

 moderate distance of the absolute zero of temperature. 



I have dwelt on the value and importance of nitrogen, but I 

 must not omit to bring to your notice those little known and 

 curiously related elements which during the past twelve months 

 have been discovered and partly described by Prof. Ramsay and 

 Dr. Travers. For many years my own work has been among 

 what I may call the waste heaps of the mineral elements. Prof. 



NO. 1506, VOL. 58] 



Ramsay is dealing with vagrant atoms of an astral nature. 

 During the course of the present year he has announced the 

 existence of no fewer than three new gases — krypton, neon, and 

 metargon. Whether these gases, chiefly known by their spectra, 

 are true unalterable elements, or whether they are compounded 

 of other known or unknown bodies, has yet to be proved. 

 Fellow workers freely pay tribute to the painstaking zeal with 

 which Prof. Ramsay has conducted a difficult research, and to 

 the philosophic subtlety brought to bear on his investigations. 

 But, like most discoverers, he has not escaped the flail of severe 

 criticism. 



There is still another claimant for celestial honours. Prof. 

 N.isini tells us he has discovered, in some volcanic gases at 

 Pozzuoli, that hypothetical element Coronium, supposed to cause 

 the bright line 53i6*9 in the spectrum of the sun's corona. 

 Analogy points to its being lighter and more diffusible than 

 hydrogen, and a study of its properties cannot fail to yield 

 striking results. Still awaiting discovery by the fortunate 

 spectroscopist are the unknown celestial elements Aurorium, 

 with a characteristic line at 55707 — and Nebulum, having two 

 bright lines at 5007*05 and 4959*02. 



The fundamental discovery by Hertz, of the electro- magnetic 

 waves predicted more than thirty years ago by Clerk Maxwell, 

 seems likely to develop in the direction of a practical appli- 

 cation which excites keen interest — I mean the application to 

 electric signalling across moderate distances without connecting 

 wires. The feasibility of this method of signalling has been 

 demonstrated by several experimenters at more than one meet- 

 ing of the British Association, though most elaborately and 

 with many optical refinements by Oliver Lodge at the Oxford 

 meeting in 1894. But not until Signer Marconi induced the 

 British Post Office and foreign Governments to try large-scale 

 experiments did wireless signalling become generally and popu- 

 larly known or practically developed as a special kind of tele- 

 graphy. Its feasibility depends on the discovery of a singularly 

 sensitive detector for Hertz waves — a detector whose sensitive- 

 ness in some cases seems almost to compare with that of the 

 eye itself. The fact noticed by Oliver Lodge in 1889, that an 

 infinitesimal metallic gap subjected to an electric jerk became 

 conducting, so as to complete an electric circuit, was redis- 

 covered soon afterwards in a more tangible and definite form, 

 and applied to the detection of Hertz waves by M. E. Branly. 

 Oliver Lodge then continued the work, and produced the 

 vacuum filing-tute coherers with automatic tapper-back, which 

 are of acknowledged practical service. It is this varying con- 

 tinuity of contact under the influence of extremely feeble 

 electric stimulus alternating with mechanical tremor, which, in 

 combination with the mode of producing the waves revealed by 

 Hertz, constitutes the essential and fundamental feature of 

 " wireless telegraphy." There is a curious and widely spread 

 misapprehension about coherers to the effect that to make a 

 coherer work the wave must fall upon it. Oliver Lodge has 

 disproved this fallacy. Let the wave fall on a suitable receiver, 

 such as a metallic wire or, better still, on an arrangement of 

 metal wings resembling a Hertz sender, and the waves set up 

 oscillating currents which may be led by wires (enclosed in 

 metal pipes) to the coherer. The coherer acts apparently by a 

 species of end-impact of the oscillatory current, and does not 

 need to be attacked in the flank by the waves themselves. This 

 interesting method of signalling — already developing in Mar- 

 coni's hands into a successful practical system which inevitably 

 will be largely used in lighthouse and marine work — presents 

 more analogy to optical signals by flash-light than to what is 

 usually understood as electric telegraphy ; notwithstanding the 

 fact that an ordinary Morse instrument at one end responds to 

 the movements of a key at the other, or, as ar'ranged by 

 Alexander Muirhead, a siphon recorder responds to an auto- 

 matic transmitter at about the rate of slow cable telegraphy. 

 But although no apparent optical apparatus is employed, it 

 remains true that the impulse travels from sender to receiver by 

 essentially the same process as that which enables a flash of 

 magnesium powder to excite a distant eye. 



The phenomenon discovered by Zeeman that a source of 

 radiation is affected by a strong magnetic field in such a way 

 that light of one refrangibility becomes divided usually into 

 three components, two of which are displaced by diffraction 

 analysis on either side of the mean position, and are oppositely 

 polarised to the third or residual constituent, has been examined 

 by many observers in all countries. The phenomenon has been 

 subjected to photography with conspicuously successful results 



