ii6 



NA TURE 



[September 22, 1904 



the difficulties of its measurement are less owing to the 

 reduction of the disturbing effects due to the surrounding 

 gas. 



Prof. Rubens gave an account of his recent work on the 

 optical properties of metals for long waves obtained by his 

 niethod of " Reststrahlen. " The radiation had about loo 

 times the wave-length of the sodium line, and it was found 

 that in this region the reflecting powers of metals are in- 

 dependent of the wave-length. In these circumstances Max- 

 well's theory gives for a good conductor i-R = 36-5/v/k.7, 

 where R is the amount reflected from the surface when 

 unit radiation is incident on it, k is the conductivity of the 

 metal, and A is the wave-length. The observations on pure 

 metals and alloys agree with the theory, and show that 

 the electrical conductivity of a metal may now be determined 

 by a measurement of its reflecting power. 



Prof. Wien, in discussing the question as to whether the 

 ether moves with the earth or not, pointed out that accord- 

 ing to the recent work of Lorentz, in which the electron is 

 assumed to be ellipsoidal in form, attempts to settle the 

 question based on interference or the rotation of the 

 plane of polarisation would be without result. He thought 

 himself the most promising method was a duplication of 

 Foucault's revolving mirror method, the reflection taking 

 place at the two ends from mirrors revolving with the same 

 velocity. If the ether has a component movement along the 

 line joining the mirrors the deflections observed at the two 

 ends should differ. 



Prof. Kayser directed attention to the defects of Row- 

 land's scale of wave-lengths in view of the accuracy now 

 attainable by interference methods of measuring 'wave- 

 lengths. He considered that concave grating spectra were 

 only suitable for interpolation purposes, and that the pre- 

 paration of a standard scale should be taken in hand at 

 once. Mr. Newall suggested that dark lines were more 

 suitable than bright ones for this purpose. 



Dr. Lummer, in describing his parallel plate spectroscope 

 for the resolution of dose spectral lines, pointed out the 

 importance of high resolution if the effects of the mode of 

 excitation or of an electrostatic field on the lines of a gas 

 are to be investigated. Dr. Lummer showed his instru- 

 ment in use in the Cavendish Laboratory, and was able 

 to detect a diff'erence between the lines of mercury, sodium, 

 hydrogen, and helium when produced by Hertzian waves 

 and when produced by the induction coil spark. 



In connection with the preparation of the plates of the 

 spectroscope. Lord Rayleigh mentioned that he had found 

 the use of dilute hydrofluoric acid very effective in putting 

 on the finishing touches to glass surfaces. 



Prof. Wood described the interference method he had used 

 to determine the dispersion of sodium vapour. The vapour 

 was produced in an exhausted tube with plane ends 

 surrounded by a wire by which the tube was electrically 

 hea'ed. Over a range extending to K^lix"^ -\J) = -iaao the 

 results agree well with the formula it"- = \ + m K'^I(k^-\J). 



The discussion on •■)i-rays" was very one sided, as no 

 one who spoke had succeeded in convincing himself that 

 any effects he may have observed were not subjective. 



Throughout the whole of the meeting communications 

 dealing with radio-activity attracted a large amount of 

 attention. Lord Kelvin described his models of radium 

 atoms to give out a and /3 rays respectively. The former 

 consisted of an " electrion " e placed at the point of contact 

 of two spheres, through the volumes of which charges 

 -4e are uniformly distributed. When equilibrium is 

 destroyed and the spheres move apart the electrion accom- 

 panies one sphere and we have the a particle. In the same 

 way if two electrions e are in equilibrium at opposite 

 extremities of a diameter of a sphere through the volume 

 of vvhich a charge -\e is uniformlv distributed, and 

 equilibrium is destroyed, one of the electrions moves away 

 from the sphere and gives the /3 ray. 



_ Prof. Schuster described his apparatus in which radium 

 is utilised in measuring the rate of production of ions in 

 the atmosphere. Changes in the state of the atmosphere 

 are found to take place much more rapidly than was antici- 

 pated, so that it is not advisable to use any method of 

 measurement which involves the constancy of the state for 

 more than five minutes. 



Prof. Thomson gave an account of the work which has 

 been done recently at the Cavendish Laboratory to determine 

 NO. 182 1, VOL. 70] 



whether ordinary matter possesses to a small extent the 

 property of radio-activity so strongly shown by radium and 

 polonium. His criterion for the possession of this property 

 is that the substance shall be capable of producing electrical 

 conductivity in the gas in a closed vessel in its neighbour- 

 hood. The difficulties of the investigation are due to the 

 wide distribution of radium in soil, water, and air, and to 

 the fact that the emanation from it settles on bodies left 

 exposed to the air. A small quantity of radio-active material 

 present in the body from either of these causes may be 

 sufficient to mask the effect due to the substance itself. 



From his observations Prof. Thomson concludes that each 

 metal gives out a specific radiation which differs in its- 

 properties from the radiation sent out by other substances, 

 and appears not to be a secondary radiation due to the 

 impact on the substance of some form of penetrating radi- 

 ation present in the atmosphere. The search for a radio- 

 active gas produced by each metal has so far proved un- 

 successful, but Prof. Thomson thinks there is some indirect 

 evidence for the existence of such a gas. 



Dr. Elster and Dr. Geitel pointed out that any results 

 obtained by the use of the conducting property of a gas 

 were open to the objection that the effects observed might 

 still be due to traces of radio-active matter left in the 

 apparatus, and not to the metals themselves. 



Prof. Thomson's description of his work was necessarily 

 much condensed, and physicists will look forward to the 

 publication of a more complete account which will set 

 aside this objection. 



On the last morning of the meeting Prof. Fleming ex- 

 hibited his apparatus for measuring the lengths of Hertzian 

 waves such as are used in wireless telegraphy. A wire 

 helix has attached to one end a metal plate which, with a 

 similar plate attached to the apparatus rn which the electrical 

 oscillations originate, forms a condenser. The effective 

 length of the helix is altered by a sliding conducting saddle, 

 and the positions of the antinodes along the helix are deter- 

 mined by a Neon vacuum tube held perpendicular to the 

 axis of the helix. From the dimensions of the helix the 

 velocity of the waves along it can be calculated, and hence 

 the frequency of the oscillation and its wave-length in air. 

 Prof. Rubens stated that a similar method had been in use 

 in Berlin for some time in connection with a portable 

 apparatus for measuring the lengths of the waves used in 

 the Slaby system of wireless telegraphy. 



From the above notes of some of the matters brought 

 forward it will be evident that the Cambridge meeting will 

 hold its own as one of the most interesting of recent vears. 



C. H. Lees. 



CHEMISTRY AT THE BRITISH 

 ASSOCIATION. 



'T'HE proceedings of Section B (chemistry) were 

 characterised not only by the general interest attach- 

 ing to the numerous papers presented, but also by the 

 unusually large attendances at the meetings, and chieflv bv 

 the presence of more than twenty distinguished Continental 

 chemists, who made several important contributions to the 

 business of the section. 



The foreign visitors included Prof. Aschan (Helsingfors), 

 Prof. Briihl (Heidelberg), Prof. Max Busch (Eriangen), 

 Prof. Dieterici (Hanover), Dr. Etard (Paris), Prof. Franchi- 

 mont (Leyden), Prof. M. Freund (Frankfurt), Prof. Gabriel 

 (Berlin), 'M. le Comte de Gramont (Paris), Prof. Groth 

 (.Munich), Prof. Guye (Geneva), Prof. Haller (Paris), Prof. 

 Kayser (Bonn), Prof. Knoevenagel (Heidelberg), Prof. Leduc 

 (Paris), Prof. Richard Meyer (Brunswick), Dr. E. Noelting 

 (Mulhausen), Prof, van Romburgh (Utrecht), Dr. Rupe 

 (Bale), Prof. I. Traube (Berlin), Prof. Walden (Riga), Prof. 

 Wedekind (Tubingen), Prof. Wegscheider (Vienna), Prof. 

 Wien (Wiirzburg), and Prof. Wolffenstein (Berlin). 



The following papers were read : — On the bearing of the 

 colour phenomena presented by radium compounds : W. 

 .'Vckroyd. On the pentavalent nitrogen atom : Prof. O. 

 ."^schan. Saponarin, a glucoside coloured blue by iodine : 

 Dr. G. Barger. The relation between the crystalline and 

 the amorphous states as disclosed by the surface flow of 

 solids : G. T. Beilby. The action of certain gases on glass 

 in the neighbourhood of hot metals : G. T. Beilby. The 

 change of conductivity in solutions during chemical re- 



