i;8 



NATURE 



[December 7, 189; 



immediately gave it its true explanation — molecules of residual 

 air, or gas, or vapour projected at great velocities ^ by electric 

 repulsion from the negative electrode. This explanation has 

 been repeatedly and strenuously attacked by many other able in- 

 vestigators, but Crookes has defended - it, and thoroughly 

 established it by what I believe is irrefragable evidence of ex- 

 periment. Skilful investigation perseveringly continued brought 

 out more and more of wonderful and valuable results : the non- 

 importance of the position of the positive electrode; the pro- 

 jection of the torrent perpendicularly from the surface of the 

 negative electrode ; its convergence to a focus and divergence 

 thenceforward when the surface is slightly [convex ; the slight 

 but perceptible repulsion betweed two parallel torrents due, 

 according to Crookes, to negative electrifications of their con- 

 stituent molecules ; the change of direction of the molecular 

 torrent by a neighbouring magnet ; the tremendous heating 

 effect of the torrent from a concave electrode when glass, metal, 

 or any ponderable substance is placed in the focus ; the 

 phosphorescence produced on a plate coated with sensitive 

 paint by a molecular torrent skirting along it ; the brilliant 

 colours — turquoise-blue, emerald, orange, ruby-red — with 

 which grey colourless objects and clear colourless crystals glow 

 on their struck faces when lying separately or piled up in a heap 

 in the course of a molecular torrent ; " electrical evapor- 

 ation ■"' of negatively electrified liquids and solids ; '* the seem- 

 ingly red-hot glow, but with no heat conducted inwards from 

 the surface, of cool, solid silver kept negatively electrified 

 in a vacuum of 1/1,000,000 of an atmosphere, and thereby 

 caused to rapidly evaporate. This last mentioned result is 

 almost more surprising than the phosphorescent glow excited by 

 molecular impacts in bodies not rendered perceptibly phos- 

 phorescent by light. Both phenomena will surely be found very 

 telling in respect to the molecular constitution of matter and the 

 origination of thermal radiation, whether visible as light or not. 

 In the whole train of Crookes' investigations on the radiometer, 

 the viscosity of gases at high exhaustions, and the electric 

 phenomena of high vacuums, ether seems to have nothing to do 

 except the humble function of showing to our eyes something of 

 what the atoms and molecules are doing. The same confession 

 of ignorance must be made with reference to the subject dealt 

 with in the important researches of Schuster and J. J. Thomson 

 on the passage of electricity through gases. Even in Thomson's 

 beautiful experiments showing currents produced by circuital 

 electromagnetic induction in complete poleless circuits, the 

 presence of molecules of residual gas or vapour seems to be (he 

 essential. It seems certainly true that without the molecules 

 there could be no current, and that without the molecules elec- 

 tricity has no meaning. But in obedience to logic I must with- 

 draw one expression I have used. We must not imagine that 

 "presence of molecules \s Ihe essential." It is certainly an 

 essential. Ether also is certainly an essential, and certainly has 

 more to do than merely to telegraph to our eyes to tell us of what 

 the molecules and atoms are about. If a first step towards 

 understanding the relations between ether and ponderable 

 matter is to be made, it seems to me that the most hopeful 

 foundation for it is knowledge derived from experiment on 

 electricity in high vacuum ; and if, as I believe is true, there is 

 good reason for hoping to see this step made, we owe a debt of 

 gratitude to the able and persevering workers of the last forty 

 years who have given us the knowledge we have : and we may 

 hope for more and more from some of themselves and from 

 others encouraged by the fruitfulness of their labours to per- 

 severe in the work. 



The President then presented the medals awarded by the 

 Society as follows : — The Copley Medal to Sir George Gabriel 

 Stokes, Bart., F. R. S., for his researches and discoveries in 

 physical science; a Royal Medal to Prof. A. Schuster, F. R. S. , 

 for his spectroscopic inquiries, and his researches on disruptive 

 discharge through gases and on terrestrial magnetism ; a Royal 

 Medal to Prof. H. Marshall Ward, F. R.S., for his researches 

 into the life-history of fungi and schizomycetes ; and the Davy 

 Medal to Prof. J. H. van't Hoffand Dr. J. A. Le Bel, in recog- 

 nition of their introduction of the theory of asymmetric carbon, 

 and its use in explaining the constitution of optically active 

 carbon compounds. 



In the evening the Fellows and their friends dined together 

 at the Whitehall Rooms, Hotel Metropole. 



1 Probably, I believe, not greater in any case than two or three kilometres 

 per second. 



- Address to the Institute of Telegraphic Engineers, 189. 

 •• Roy. Soc. Proc. , June 11, 1S91. 



7-HE TEMPERATURE OF IGNITION OF 

 EXPLOSIVE GASEOUS MIX7URES. 



A N important contribution to our knowledge of this subject 

 is communicated to Xhe. Berichte by Prof Victor Meyer of 

 Heidelberg, in conjunction with his assistant, Herr A. Miinch. 

 The interesting experiments which were carried out some eight- 

 een months ago in the Heidelberg laboratory, concerning the 

 conditions under which the explosion or silent combination of 

 gaseous mixtures occurs, left the question of the precise tempera- 

 tures of explosive combination undetermined, inasmuch as the 

 necessary high temperatures were attained by the use of boiling 

 salts whose temperatures of ebullition lay a considerable number 

 of degrees apart. The researches have since been continued 

 under conditions in which it has been found possible to deter- 

 mine the actual temperatures with precision. In these experi- 

 ments any possibility of the occurrence of appreciable amounts 

 of silent combination has been avoided, in order that the deter- 

 minations of the temperature of explosive combination might be 

 unaffected by errors due to that cause. The conspicuous novelty 

 of the method adopted consists in placing the small bulb contain- 

 ing the mixture to be exploded inside the larger bulb of the air 

 thermometer employed to determine the temperature, thus at once 

 ensuringthattheexplosion bulb and the thermometer bulb shall be 

 heated to precisely the same temperature. The objection which at 

 first suggests itself, that the heat suddenly developed at the 

 moment of explosion might exert a disturbing influence upon 

 the indications of the air thermometer, was proved,by direct and 

 repeated experiment to be without validity, such disturbance being 

 found to be too small to be measured. The bulb in which the 

 explosion is brought about is not closed, for the explosion of such 

 detonating mixtures of gases at rest, that is to .'^ay, confined tea 

 closed space, is so violent that if the glass escapes pulverisation it 

 is much distorted, owing to the temperature to which it requires 

 to be heated being about its softening point. The distortion 

 usually takes the form of a shrinking from two opposite points, 

 where the glass is drawn in and distended to such an extent as 

 to produce two internal spheres. Such deformation would of 

 course alter considerably the volume of the air thermometer. 

 This is avoided by attaching a long stem to the bulb, open at 

 the free extremity, and of passing a slow current of the gaseous 

 mixture through the apparatus. The bulb of the thermometer 

 was heated by means of a bath of a fused alloy consisting of 

 equal parts of tin and lead, and it was found immaterial whether 

 the thermometer was directly immersed in the molten metal or 

 protected by means of a closely-fitting refractory metal sheath. 

 The estimation of the temperature was effected by displacing 

 the air of the thermometer, whose volume was known, by means 

 of a current of hydrochloric acid gas, and measuring its volume 

 over distilled water which had recently been freed from air by 

 boiling. 



The first series of experiments were made with the detonating 

 electrolytic mixture of hydrogen and oxygen. The gases were 

 freed from ozone by passage through a solution of potassium 

 iodide. They were then washed through water, with which a 

 Woulfe's bottle was almost filled, after which they traversed a 

 tube packed with numerous discs of brass gauze, which were 

 found effectual in preventing the explosion from travelling back 

 to the Woulfe's bottle. The mixed gases were then allowed to 

 enter the explosion bulb by means of a capillary tube passing 

 down the stem to the bottom of the bulb. The rapidity of the 

 gaseous stream was found to exert no influence upon the tem- 

 perature of explosion, within the limits imposed by the mode 

 of experimenting. The bath was then gradually raised to the 

 neighbourhood of the combining temperature, and the instant 

 the explosion ensued the air contained in the thermometer was 

 displaced by hydrogen chloride, collected over water in the 

 measuring vessel, and its volume ascertained on the attainment 

 of atmospheric temperature and pressure. By displacing the 

 air the instant the detonation was heard, any appreciable 

 augmentation of the temperature during the moment of explosion 

 was prevented. 



As the result of several series of experiments carried out with 

 four distinct sets of apparatus, the temperature of explosion of 

 electrolytic hydrogen and oxygen is found to vary from 612° to 

 686°. It would thus appear, conformable with the supposition 

 of Prof. Van t'Hoff from theoretical considerations, that this 

 mixture is incapable of exhibiting a sharply fixed temperature 

 of explosion. Moreover, it makes no difference whether the 

 mixture is dry or moist ; for if dried a small amount of silent 



NO. 1258, VOL. 4q] 



