March 31, 



189S] 



.VA TURE 



525 



SOCIETIES AND ACADEMIES 

 London. 



Physical Society, March 25.— Mr. Shelford Bidwell, 

 President, in the chair. — Mr. A. A. Campbell Swinton read 

 a paper and showed experiments upon the circulation of 

 gaseous matter in a Crookes' tube. The stream-lines within a 

 Crookes' tube are investigated by observing the direction and 

 speed of rotation of a mica radiometer-mill, mounted on a 

 sliding-rod, so that it can be moved along a line at right angles 

 to the line joining the electrodes. The axis of the mill is at 

 right angles to both these lines. If the mill is adjusted to a 

 position between the flat plate and the cup electrodes, with its 

 axis just sufficiently low to prevent equal and opposite simul- 

 taneous actions on the top and bottom vanes, it rotates always 

 in the direction indicating a stream from kathode to anode. 

 The speed is greater when the flat plate is the kathode. If, 

 however, the mill is now moved below this line, a point is 

 reached at which rotation ceases, and below this neutral point 

 the rotation is suddenly reversed. Reversal is only to be ob- 

 served with high degrees of exhaustion ; the rotation is never 

 so rapid here as in the first position. The mill rotates, and the 

 reversal may be observed, whether cup or plate is made kathode, 

 and the direction of rotation below the neutral point is always 

 opposite to that in the position above it. A small Wimshurst 

 machine is as eflective as an induction coil in producing these 

 effects. The experiments are intended to establish the exist- 

 ence, at high degrees of exhaustion, of a true anode-stream, i.e. 

 a stream that travels from anode to kathode just in the same 

 manner as the kathode-stream flows from kathode to anode. 

 This anode- stream is charged positively; it is exterior to the 

 kathode-stream ; its velocity is less than that of the kathode- 

 scream, but its velocity increases as the vacuum is improved. 

 It seems probable that, in high vacua, some portion of the 

 positive electricity passing through the tube, is carried by the 

 positively charged atoms or particles that constitute the anode- 

 stream. At lower degrees of exhaustion, the discharge passes 

 through the tube chiefly by interchange of charges from mole- 

 cule to molecule — a Grothiis chain. At very high vacua, how- 

 ever, when the mean free path is considerable, there may be 

 to some extent a regular and complete circulation of posi- 

 tive and negative atoms, some of which pass from anode 

 to kathode, and vice versa, and deliver up their charges, 

 not by interchange, but by direct convection, to the electrodes of 

 oppo.site sign. Prof. Boys said he did not feel altogether con- 

 vinced by the experiments, that the rotation of the mill was due 

 to simple mechanical motion of the particles of matter between 

 the electrodes. The weight of air left in the tube at such high 

 degrees of exhaustion was extremely small ; it was difficult to 

 realise that its impact could produce the sudden mechanical effect 

 observed at the moment of the reversal of the rotation of the 

 mill. Mr. Wimshurst thought it important to keep in mind the 

 existence of mercury-vapour in the tube. He also referred to 

 some experiments in which a bar of metal was used to explore a 

 focus-tube, by observation of the changes of luminosity produced 

 in diffierent positions. Dr. Chree said that if the rotations of 

 the mill could be shown to indicate a velocity of the particles, of 

 the same order as that observed in Crookes' experiments, it was 

 safe to assume the existence of a similar cause. This might be 

 important in deciding as to the general truth of the bombardment 

 theory of Crookes. He asked whether the rotation had been 

 investigated within the dark space around the kathode. Mr. 

 Appleyard suggested that in tracing the cause of the rotation 

 it would lead to simpler results if the vanes of the mill were 

 made of some light conducting substance. Mica introduced 

 difficulties owing to its retention of the charges. Prof. Boys 

 pointed out that this could be done by gilding the mica. Mr. 

 Campbell Swinton, in reply, said that the objection raised by 

 I'rof. Boys to the mechanical theory of the rotation would apply 

 equally to the whole theory of electro-radiometry, including the 

 case of the mill used originally by Crookes in the direct path of 

 the kathode-stream. But it must be remembered that although 

 the mass of matter present within the tube was very small, its 

 velocity was proportionately great, it was of the order of 9000 

 kilometres per second ; hence the contained matter might be 

 conceived as capable of producing the observed acceleration, 

 and Crookes' bombardment theory might with safety be adopted 

 as a good working hypothesis. In the tubes used for these ex- 

 periments, the exhaustion was carried so high that the negative 

 dark space appeared to fill the whole tube. He had, so far, 



NO. 1483, VOL 57] 



only tried mica for the vanes, but he thought it would be im- 

 portant to observe the result with a substance that did not 

 retain the charges. — Mr. .\. Stansfield then read a paper on 

 thermo-electric pyrometers. In obtaining photographic records 

 of the readings of thermo-electric pyrometers, the range of 

 measurement is limited by the size of the photographic plate. 

 For long ranges of temperature, the sensitiveness of the galva- 

 nometer must therefore be small. When it is desired to examine 

 the temperature changes in detail — as, for instance, at the melt- 

 ing-points and freezing-points of metals — it is necessary to 

 employ some device for giving a more open scale for the short 

 temperature ranges that include those particular points. For 

 this purpose two galvanometers are arranged in parallel, and so 

 that they have their deflections recorded on the same photo- 

 graphic plate. The less sensitive galvanometer covers the 

 entire range of temperature throughout an observation ; the 

 other is brought into use for magnifying special portions of the 

 range. In this latter case, part of the electromotive force of 

 the thermocouple is compensated by an opposing electromotive 

 force, applied at two points of the circuit, from a battery of 

 Clark cells in series with a high resistance. The recording 

 apparatus consists of a photographic plate mounted on a float 

 that rises steadily when water is admitted into a cylinder. The 

 source of light is a glow-lamp, enclosed in a wooden box. A 

 brass tube, with a rectangular diaphragm at the end nearest the 

 lamp, cuts off all light except that from a selected piece of 

 vertical filament. Light from this filament is reflected by the 

 plane galvanometer-mirror, and is focussed upon the photo- 

 graphic plate by a lens in front of the galvanometer ; this , 

 method was suggested by Prof. Boys. The "cold" junctions 

 of the thermo-couple are both inserted into a hypsometer. Very 

 serious discrepancies exist between the indications of couples 

 having nominally the same composition ; they are too great to 

 be attributed to accidental differences in the constitution of the 

 alloys. Although with platinum alloys, coupled with platinum,. 

 10 per cent, of iridium gives a more powerful couple than 

 10 per cent, of pure rhodium, the partial substitution of iridium 

 for rhodium very considerably lowers its thermo-electric power. 

 This result suggests that the change in the thermo-electric power 

 of a metal depends upon the extent to which it is saturated with 

 the alloying metal ; thus 10 per cent, either of rhodium or 

 iridium would, per se, more completely saturate the platinum 

 than would 10 per cent, of a mixture of the two metals. The 

 author discusses a series of curves derived from his experiments. 

 He concludes that, thermo-electrically, there may be two classes 

 of metals : (l) the ordinary metals, for which the curve repre- 

 senting the first differential of electromotive force with respect 

 to temperature is a straight line, and (2) the platinum metals,,^ 

 together with a few, such as nickel and cobalt, for which the 

 curve of this differential multiplied by the absolute temperature 

 is a straight line. Dr. Chree discussed the curves, and asked how 

 far stirring affected the results ; he was inclined to think that 

 stirring was a mistake. Mr. A. Campbell inquired whether the 

 galvanometer kept its zero sufficiently well throughout the 

 tests. Mr. Stansfield, in reply, said heihad also come to- 

 the conclusion that stirring was a mistake ; and it was a mistake 

 to use a large quantity of metal. The pyrometers were sensitive 

 to about a tenth of a Centigrade degree. He had experienced ^ 

 great difficulty with the zero of the galvanometer. — The Presi- 

 dent proposed votes of thanks to the authors, and the meeting^ 

 adjourned until April 22. 



Chemical Society, March 17. — Prof. Dewar, President, 

 in the chair. — The following papers were read : — The reduction 

 of bromic acid and the law of mass action, by Miss W. Judson 

 and J. W. Walker. The reduction of bromic acid by hydro- 

 bromic acid constitutes a bimolecular reaction in presence 

 of much sulphuric acid, and a tetramolecular reaction! 

 in absence of sulphuric acid. — The action of ferric 

 chloride on the ethereal salts of ketone acids, by R. S. 

 Morrell and J. M. Crofts. In dry ethereal solution, ferric 

 chloride acts on ethylic ketophenylparaconate with production 

 of a substance, FeCUCuHuOj, which is decomposed by watet 

 yielding the basic ferric salt of ethylic phenylparaconate, 

 Fe(OH) (Ci3Hji05)2 ; analogous results are obtained with the 

 ethylic salt of the lactone of oxalcitric acid. — Note on the 

 volatility of sulphur, by T. C. Porter. Sulphur sublimes 

 rapidly at 100° in a vacuum. — Cannabinol, by T. B. Wood, 

 W. T. N. Spivey and T. H. Easterfield. Cannabinol, the toxic 

 resinous constituent of Indian hemp, boils at 400°, and its 

 vapour density points to the molecular composition CjgHj^Oj ^ 



