Willams-Crookes · Source catalogue

Crookes's public lecture on the behaviour of gas in tubes pumped to very high exhaustion, shown as live demonstrations with an induction coil and electric lantern. He starts from Faraday's 1816/1819 speculation that matter has four states (solid, liquid, gaseous, radiant) and argues that at about one millionth of an atmosphere the mean free path of the residual molecules becomes comparable to the vessel, so the molecules must be treated individually and the gas behaves as a 'fourth state'. He identifies the dark space round the negative pole with the mean free path. Demonstrations: green or coloured phosphorescence of glass, diamond, ruby, phenakite, spodumene, emerald and calcium sulphide under 'molecular bombardment' (the ruby shows one intense red line at about 6,895, units unstated); rays that travel in straight lines from the negative pole normal to its surface, cast shadows (hinged aluminium cross, glass 'fatigue') and come to a focus; mechanical action (mica paddle wheel on a glass railway, an electrical radiometer, vanes spun by a red-hot platinum ring); deflection by a magnet likened to a bullet trajectory; two parallel streams that repel, taken to show negatively charged molecules rather than current carriers; intense heating at the focus (wax melted, glass perforated, iridio-platinum melted). Numbers given: best phosphorescence about 1 millionth of an atmosphere; highest vacuum 1/20,000,000 atmosphere as printed (the digest's 1/6,754,000 is an OCR error); a 13.5 cm bulb holds about 1.29 x 10^24 molecules at ordinary pressure and about 10^18 at one millionth (the digest's 10^15 is wrong); filling through a pinhole at 100 million molecules a second would take about 408 million years. Apparatus by Mr. Gimingham. No pump, gauge, coil voltage, ray velocity or focus temperature is given and no tabulated data appear; all results are qualitative demonstrations. Closes with the 'border-land where matter and force seem to merge'. Added after QE (all [read]): (1) Non-conducting vacuum, pp.7-8. Phosphorescence is strongest near one millionth of an atmosphere (printed table: 1 millionth atm = 0.00076 mm Hg; 1315.789 millionths = 1 mm; checked on the page image) and then 'begins to diminish until the spark refuses to pass'. In the potash tube (Fig. 5) 'nothing is visible - the vacuum is so high that the tube is non-conducting'; warming the potash to release 'a trace of aqueous vapor' makes 'conduction commence instantly', and on cooling he describes, but does not show, 'the vacuum becoming non-conducting'. A footnote quotes William Morgan, Phil. Trans. 1785, vol. lxxv p.272, on the 'non-conducting power of a perfect vacuum': in a boiled mercury gauge 'neither the smallest ray of light, nor the slightest charge, could ever be procured'; with air admitted the light ran green, blue, indigo, violet, purple, and finally conduction ceased again when the medium was 'so dense'. No pressure is given for the point where the spark fails. (2) Low against high vacuum, pp.9-10: in bulb A (a few mm Hg) a line of violet light follows the positive pole; in bulb B (about a millionth atm) the green patch is unchanged when the positive wire is moved, so 'the phenomena seem to depend entirely on the negative pole'; stratifications and cloudy luminosity 'disappear entirely'. A related magnetic contrast on p.17: in a low vacuum the deflected discharge 'rises and pursues its path to the positive pole', in a high vacuum the deflected stream 'did not recover itself, but continued its path in the altered direction'. (3) Chemical absorbents, p.21: highest exhaustion was reached by absorbents in the tube (phosphoric anhydride for water vapour, potash for carbonic acid, palladium for hydrogen, carbon and potash for oxygen), 'to much higher degrees than I can get by mere pumping'. (4) 'Three hundred trillions a second' (pp.22-23): Crookes uses long-scale words (a quadrillion = 10^24, a trillion = 10^18); at 3 x 10^20 per second his 1.288 x 10^24 molecules would enter in about 4,300 s, about 72 minutes [calc from the printed figures], matching his 'before you leave this room'. (5) Fig. 13 hot-ring test, pp.14-15: ring-to-vane distance, pressure ('exhausted to a very high point'), battery cells or voltage, ring temperature ('red-hot'), rotation speed and direction are not given, and no control (cold ring, shield, reversed fly) is described; with the coil 'disconnected' the vanes 'spin as fast as they did when the induction-coil was at work'. Vanes are four clear mica squares at 45 degrees. In Fig. 12 the mica face stays dark and the bare metal face carries the violet glow; direction of turning is not stated. (6) Fig. 18 two-cathode tube, pp.18-19: two negative terminals a, b 'close together' at one end, positive terminal c at the other; no distance, pressure, voltage, coil setting or angle is given. First ray (a) 'jumps up from its first position, d f, to d g' when b is switched on; the lower ray is only asserted ('if time permitted I could show you that the lower ray is also deflected'). The engraving suggests the displacement is zero at the slit and grows along the screen, but the labelling is ambiguous; no test with b connected but shielded, or at another potential, is described. Crookes states the cause as mutual repulsion of two negatively electrified streams. Other notes: the 'last year's President' at Dublin (p.4) is William Spottiswoode [memory, high]; a diamond 'shines with as much light as a candle' (p.6); Crookes credits Gimingham with the hinged cross (Fig. 9, p.12), the railway paddle wheel (Fig. 11, p.13) and the magnetic wheel (Fig. 17, p.17), and not with any cup-cathode or focusing tube.

Key claims

• At exhaustion near one millionth of an atmosphere the residual gas is in a 'fourth state' (radiant matter) as far removed from gas as gas is from liquid.
• The dark space round the negative pole is the mean free path of the residual gas molecules, and it lengthens and shortens with the vacuum.
• Radiant matter leaves the negative pole in straight lines normal to its surface, regardless of the position of the positive pole, and casts sharp shadows.
• Radiant matter striking glass, diamond, ruby and other minerals produces phosphorescence in a colour characteristic of the substance, strongest at about one millionth of an atmosphere.
• Radiant matter exerts mechanical force: it drives a paddle wheel up a slope and spins radiometer vanes, and a red-hot platinum ring spins vanes as fast as the induction coil does.
• The stream is deflected by a magnet, with a curve that increases as residual gas slows the molecules, as for a projectile.
• Two parallel streams repel each other, so the streams are negatively electrified molecules, not current-carrying wires.
• The molecular focus is intensely hot: it melts wax, perforates glass and melts iridio-platinum.
• Phosphorescence, shadows and magnetic deflection are the same whether the residual gas is hydrogen, carbonic acid or air, only beginning at different pressures.
• A 13.5 cm bulb at one millionth of an atmosphere still holds about 10^18 molecules, so the molecules must be extremely small.
• At the highest exhaustion the tube becomes non-conducting and the spark refuses to pass; admitting a trace of vapour restores conduction instantly (pp.7-8; William Morgan, Phil. Trans. 1785, is quoted as precedent).
• Chemical absorbents in the tube (phosphoric anhydride, potash, palladium, carbon) carry the exhaustion beyond what pumping alone reaches (p.21).
• In a low vacuum the discharge follows the positive pole and is a current-carrying column that, when deflected by a magnet, returns toward the positive pole; in a high vacuum the stream does not depend on the positive pole and, once deflected, keeps its altered direction (pp.9-10, 17).
• When the second negative terminal is switched on in the Fig. 18 tube, the first ray is displaced away from it (d f to d g); Crookes attributes this to mutual repulsion of two negatively electrified streams (pp.18-19).

Relevance: The sole document in the project and the primary source for Crookes's radiant-matter claims. It is a lecture of demonstrations, not a measurement paper: it states observations and a molecular-bombardment interpretation, so the physics (cathode rays, charged particles, mean free path, vacuum physics) must be reconstructed from qualitative descriptions. Printed pages 13-24 and 157-166 of PSM vol. XVI (PDF pp.1-12 and 13-22); PDF p.23 is unnumbered (it would be p.167).

Mainstream conflict: The 'fourth state of matter' framing is not used by mainstream physics (a rarefied gas is a gas, and the beam is now treated as electrons, discovered later, with a different mass and charge); the lecture's observations (straight-line travel, shadows, magnetic deflection, fluorescence, mutual repulsion) agree with later accounts of cathode rays. That judgement is for the reviewers.