November 8, 1900] 



NATURE 



51 



rays. The mean value of the energy required to produce an ion 

 in air ate atmospheric pressure and temperature was found to be 



1*90 X io~"" ergs 



This value is much greater than the energy required to pro- 

 duce hydrogen and oxygen ions in the decomposition of water. 



The ionic energy of air was found to be approximately the 

 same from pressures of one-half to three atmospheres. 



The method of determining the ionic energy for other gases 

 is described, and the evidence that the "ionic energy "is the 

 same for all gases is discussed. 



Emisston of Energy from Radio-active Substances. 



The velocity of the ions produced by Rontgen and uranium 

 radiation in air has been shown to be the same. The ions are 

 thus probably the same, and it is a reasonable assumption that 

 the same energy is required in both cases to produce them. On 

 this assumption the energy radiated by the radio-active sub- 

 stances can be determined. 



The radio-active material was spread over a known area and 

 the maximum current produced between the parallel plates 

 determined. The number of ions produced, and consequently 

 the energy to produce them, can be calculated. 



For a thick layer of uranium oxide (36 grammes spread over 

 a surface of 38 cm.) the energy radiated into the gas for i sq. 

 cm. ) of the surface is 



io~^^ calories per second. 



This amount of energy would suffice to raise i c.c. of water 

 1° C. in 3000 years, assuming no loss of heat by radiation. 

 From observations on the current due to a very thin layer of 

 uranium oxide it is shown that the energy radiated into the gas 

 is not less than 0032 calorie per year for every gramme of the 

 substance. 



The energy radiated from thorium and radium is also considered, 

 and the presence of the rays from radium deflected by a magnet 

 is taken into account. 



In the case of radium, which is 100,000 times more radio- 

 active than uranium, the emission of energy per gramme of the 

 substance is not less than 3000 calories per year. 



Distance between the Charges of the Ions in a Molecule. 



On the assumption that the energy absorbed in producing an 

 ion is due to the work done in separating the ions against the 

 forces of their electrical attraction, it can be shown that the 

 mean distance between the charges of the ions in the mole- 

 cule is 



II X io~^ cm. 



This is only 1/30 of the probable diameter of the atom. This 

 result is in accordance with the view recently advanced by J. J. 

 Thomson, that ionisation is produced by the removal of a nega- 

 tive ion from the molecule, and that the negative ion is only a 

 small fraction of the mass of an atom. 



Minimum Potential required to produce a Spark. 



If the production of ions is necessary before a spark can pass, 

 it can readily be deduced from the value of ionic energy that a 

 spark cannot pass for a potential difference less than 175 volts. 

 Experiments have shown that the minimum value is over 300 

 volts The theoretical value is of the same order, but from the 

 complexity of the phenomena a very close agreement could not 

 be expected. 



Efficiency of a Fluorescent Screen. 



Photometric comparisons were made of the light from a fluo- 

 rescent screen, excited by the X-rays, with the standard 

 Hefner-Alteneck amyl lamp. The energy of the visible 

 radiation from the amyl lamp has been determined in abso- 

 lute measure by Tumlirz {Wied. AnnaL, vol. 38, p. 640), and 

 the energy of the rays was measured by the method explained 

 earlier in the paper. From these results the efficiency of the 

 transformation of X-rays into visible light (compared with the 

 amyl lamp) was found to be 



4*4 per cent. 



A method of determining the intensity of X-rays in absolute 

 measure by photometric observations is explained. 



NO. 1619, VOL. 63] 



Entomological Society, October 17. — Mr. G. H. Verrall, 

 President, in the chair. — Mr. A. H. Jones exhibited a series of 

 Pararge viaera, a light form resembling P. megoera from the 

 Basses Alpes and the Cevennes ; a dark form approaching P. 

 hiera from Cortina ; and an intermediate form from the Italian 

 Lakes ; also a variety of Lycaena corydon, female, in which the 

 under wing showed a decided blue coloration, taken at Lago di 

 Loppio near Riva. Dr. Chapman suggested that the union 

 between the three named species of Pararge was very near, if the 

 species were not indeed identical. — Mr. A. J. Scollick exhibited 

 a specimen of Cethosia cyane, a species inhabiting North-West 

 India, which had been taken this year on the wing near Norwich. 

 It was suggested by Mr. Distant that this was a case of acciden- 

 tal importation, probably in the pupal condition. — Mr. H. Row- 

 land-Brown exhibited specimens of Erebia glacialis, taken this 

 year on the Stelvio pass, showing transitional forms to the var. 

 Alecto. He said that the typical form and the variety were not 

 found flying together, but on opposite sides of the valley. Dr. 

 Chapman observed that the darker specimens approached to the 

 form of E. melas found in the neighbourhood of Cortina-di-Am- 

 pezzo. Specimens of E. glacialis also exhibited from Saas F6e 

 and Evolena showed marked inferiority in size and brilliancy 

 of colour. — Mr. W. L. Distant exhibited a piece of Hawkesbury 

 sandstone from Australia, showing the borings of Termites, and 

 in connection with the same communicated a note from the 

 Proceedings of the Linnean Society of New South Wales (Pt. iii. 

 1899, p. 418), as follows: — " Mr. D. G. Stead exhibited speci- 

 mens of Hawkesbury sandstone (i) From the sea-shore between 

 tide marks showing the tunnelling of Marine Isopods [Sphae- 

 roma) with the living animals tn situ ; and (2) from the hill-tops 

 overlooking Port Jackson, offering examples of the borings 

 which so often attract notice and the production of which has 

 been attributed to Hymenoptera, and also to the Termites. 

 Since last meeting Mr. Stead reported that he had investigated 

 the matter and that, after breaking up a quantity of stone, he had 

 come upon Termites, of a species at present undetermined, 

 actually at work, specimens of which he exhibited. — Mr. M. 

 Burr exhibited a male and kmaXt s'ptcimen oi Anisolabis colosseay 

 Dohrn. , from New South Wales — the largest known earwig ,in 

 the world. 



Paris. 



Academy of Sciences, October 29.— M. Maurice Levy in 

 the chair. — On a method of Riemann and on linear partial 

 differential equations, by M. R. Liouville. — The application of 

 the interference method to the measurement of wave-lengths iik 

 the solar spectrum, by MM. A. Perot and Ch. Fabry. The 

 method described permits of the direct comparison of the wave- 

 length of a given dark line in the solar spectrum with a knowiv. 

 cadmium ray, a single experiment requiring only the measure- 

 ment of the diameters of two rings. — On the ammoniacal« 

 arsenates of nickel, by M. O. Ducru. Nickel forms three 

 ammoniacal arsenates corresponding to those previously 

 described for cobalt. — On the selenides of cobalt, byM. Fonzes- 

 Diacon. Cobalt combines with selenium giving according to- 

 the conditions of the experiment CoSe2,Co.2Se3,Co3Se4, and, 

 CoSe. At a high temperature all these selenides are reduced 

 by hydrogen to CogSe, which, after prolonged contact with the 

 gas, loses all its selenium. — Modification of the chemical 

 properties of some simple bodies by the addition of very small 

 proportions of foreign substances, by M. Gustave LeBon. 

 Magnesium and aluminium amalgams behave differently, from 

 either of their constituents taken singly, towards water and air. — 

 Cellulose, precipitated cellulose and hydrocellulose, by M. Leo 

 Vignon. The reducing properties, velocity of saccharification, 

 and heats of combustion of cellulose that had been submitted to 

 different modes of treatment were determined. Solutions of 

 strong alkali produced apparently a polymerisation, and similar 

 effects were caused by dilute acids, but none of these cellu- 

 loses possessed any reducing properties, and thus were sharply 

 differentiated from the oxycelluloses. — On two ketones contain- 

 ing the acetylene grouping, acetyl-oenanthylidene and benzoyl- 

 oenanthylidene. Transformation into j3-dikelones by hydration^ 

 by MM. Ch. Moureu and R. Delange. Aniylacetylene 

 CH3.(CH2)4 — C = CH is converted into its sodium derivative, 

 and this, suspended in ether and treated with the acid 

 chloride, gives the corresponding ketone. With strong 

 sulphuric acid these ketones are hydrolysed, giving the 6- dike- 

 tones C5Hii.CO.CH,.CO.CH3and CsHu.CO.CHj.CO.QHs.— 

 Transformation of a amido-acids into phenylhydantoins, by 

 M. s A. Mouneyrat. A description of the preparation and 



