Sept. 4, 1879] 



NATURE 



439 



rays is projected alonj the tuV>e. I turn the magnetism on, and 

 draw the focus to the side of the glass. The first thing you see 

 is a small circular patch melted in the coating of wax. Tlie 

 glass soon begins to disintegrate, and cracks are shooting star- 

 wise from the centre of heat. The glass is softening. Now the 

 atmospheric pressure forces it in, and now it melts. A hole (e) 

 is perforated in the middle, the air rushes in, and the experiment 

 is at an end. 



I can render this focal heat more evident if I allow it to play 

 on a piece of metal. The bulb (Fig. 2l) is furnished with a 

 negative pole in the form of a cup («). The rays will therefore 

 be projected to a focus on a piece of iridio-platinum [b) sup- 

 ported in the centre of the bulb. 



I first turn on the induction coil slightly, so as not to bring out 

 its full power. The focus is hdw playing on the metal, raising 

 it to a white heat. I bring a small magnet near, and you see I 

 can deflect the focus of heat just as I did the luminous focus in 

 the other tube. By shifting the magnet I can drive the focus up 

 and down, or draw it completely away from the metal, and leave 

 it non-luminous. I withdraw the magnet, and let the molecules 

 have full play again ; the metal is now white hot. 1 increase 



Fig. 21. 



the intensity of the spark. The iridio-platinum glows with almost 

 insupportable brilliancy, and at last melts. 



Tin Chemistry of Radiant Matter 

 As might t)e expected, the chemical distinctions between one 

 kind of radiant matter and another at these high exhaustions are 

 difficult to recogni^e. The physical properties 1 have been elu- 

 cidating seem to be common to all matter at this low density. 

 \Vhether the gas originally under ex()eriment be hydrogen, car- 

 bonic acid, or atmospheric air, the phen^jmena of phosphorescence, 

 shadows, magnetic deflection, &c., are identical, only they com- 

 mence at different pressures. Oiher facts, however, show that 

 at this low density the molecules retain their chemical character- 

 istics. Thus by introducing into the tubes appropriate absorbents 

 of residual gas, I can see that chemical attraction goes on long 

 after the attenuation has reached the best stage for showing the 

 phenomena now under illustrati >n, and I am a'jle by this means 

 lo carry the exhaustion to much higher degrees that I can get by 

 mere ])umping. Working with a<|ueous vapour I can use phos- 

 phoric anhydride as an absorbent ; » ith carbonic acid, potash ; 

 ivith hydrogen, palladium ; and with oxygen, carbon, and then 

 potash. The higlie.-.t vacuum I have yet succeeded in obtaining 

 has been the i-20,ooo,oooth of an atmosphere, a degree which 

 may be better understood if I say tliat it corresiwnds to about 

 the hundredth of an inch in a barometric column three miles 

 high. 



It may be objected that it is hardly conistcnt to attach primary 



importance to the presence of Matter, when I have taken extra- 

 ordinary pains to remove as much matter as possible from these 

 bulbs and these tubes, and have succeeded so far as to leave only 

 about the one-millionth of an atmosphere in them. At its ordi- 

 nary pressure the atmosphere is not very dense, and its recogni- 

 tion as a constituent of the world of matter is quite a modern 

 notion. It would seem that when divided by a million, so little 

 matter will necessarily be left that we may justifiably neglect the 

 trifling residue and apply the term vacuum to space from which 

 the air has been so nearly removed. To do so, however, would 

 be a great error, attributable to our limited faculties being 

 unable to grasp high numbers. It is generally taken for granted 

 that when a number is divided by a million the quotient must 

 necessarily be small, whereas it may happen that the original 

 number is so large that its division by a million seems to make 

 little impression on it. According to the best authorities, a bulb 

 of the size of the one before you (I3'S centimetres in diameter) 

 contains more than 1, 000,000, ooo,ooo,ocx3,coo, 000, 000 (a quadril- 

 lion) molecules. Now, when exhausted to a millionth of an 

 atmosphere we shall still have a trillion molecules left in the 

 bulb — a number quite sufficient to justify me in speaking of the 

 residue as matter. 



To suggest some idea of this vast number I take the exhausted 

 bulb, and perforate it by a spark from the induction coil. The 

 spark produces a hole of microscopical fineness, yet sufficient to 

 allow molecules to penetrate and to destroy the vacuum. The 

 inrush of air impinges against the vanes, and sets them rotating 

 after the manner of a windmill. Let us suppose the molecules 

 to be of such a size that at every second of time a hundred mil- 

 lions could enter. How long, think you, would it take for this 

 small vessel to get full of air ? An hour ? A day ? A year ? 

 A century ? Nay, almost an eternity ! A time so enormous 

 that imagination itself cannot grasp the reality. Supposing this 

 exhausted glass bulb, indued with indestructibility, had been 

 pierced at the birth of the solar system ; supposing it to have 

 been present when the earth was without form and void ; sup- 

 posing it to have borne witness to all the stupendous changes 

 evolved during the full cycles of ge ilogic time, to have seen the 

 first living creature appear, and the last man disappear ; sup- 

 posing it to survive until the fulfilment of the mathematician's 

 prediction that the sun, the source of energy, four million 

 centuries from its formation, will ultimately become a burnt-out 

 cinder ; ' supposing all this— at the rate of filling I have just 

 described, 100 million molecules a second — this little bulb even 

 then would scarcely have admitted its full quadrillion of mole- 

 cules.' 



But what will you say if I tell you that all these molecules, 

 this quadrillion of molecules, will enter through the microscopic 

 hole before you leave this room ? The hole being unaltered in 

 size, the number of molecules undiminished, this apparent para- 

 dox can only be explained by again supposing the size of the 

 molecules to be diminished almost infinitely — so that instead of 

 entering at the rate of 100 millions every second, they troop in 

 at a rate of something like 300 trillions a second. I have done 

 the sum, but figures when they mount so high cease to have any 

 meaning, and such calculations are as futile as trying to count 

 the drops in the ocean. 



In studying this fourth state of matter we seem at length to 

 have within our grasp and obedient ti our control the little indi- 

 visible particles which with good warrant are supposed to con- 

 stitute the physical basis of the universe. We have seen that in 

 some of its properties radiant matter is as material as this table, 

 whilst in other properties it almost assumes the character of 

 radiant energy. We have actually touched the borderland where 

 matter and force seem to merge into one another, the shadowy 

 realm between Known and Unknown which for me has always 



* The possible duration of the sun from formation to extinction has been 

 variously estimated by different authorities, at from 18 million years to 400 

 million years. For the purpose of this illustration 1 have taken the highest 

 estimate, 



* According to Mr. Johnstone St3ney(/'>4/7. Mag., vol, 36. p. 141), i c.c. of 

 air contains about 1,000,000.000,000,000,000.000 molecules. Therefore a bulb 

 13-5 ceiitims, diameter contains 13-5' kg 5236X 1.000,000,000,000,000,000,000 

 or 1,288,252,350,000.000,000.000,000 molecules of air at the ordinary pressure. 

 Therefore the bulb when exhausted to the millionth of an atmosphere, contains 

 1,288, J52,35o.coo.ooo.ooom)lecule5. leaving 1,288,251,061,747,650,000,000.000 

 mileculcs to enter through the perforation. At the rate of 100,000,000 mole- 

 cules a second, the time required for them all t-i enter will b« 



12,882,510,617,476,500 .seconds, or 

 ^ «14. 708. 510.291. 275 minutes, or 



3,578.475.171,531 hours, or 

 149,10^,132.147 days, or 

 4 >8, 501,731 years. 



