6i8 



NATURE 



[February 5, 1920 



and gives the identical relation between the strain 

 components expressed in the various systems of co- 

 ordinates. The various possible stress sets in rect- 

 angular and polar co-ordinates are then set forth in 

 order, after which the solutions in orthogonal curvi- 

 linears are obtained in such a manner as generally to 

 show their connection with those formerly given. The 

 second part of the paper applies the results obtained 

 to the solution of some examples. — F. Horton and 

 Ann C. Davies : An investigation of the effects of 

 electron collisions with platinum and with hydrogen, 

 to ascertain whether the production of ionisation from 

 platinum is due to occluded hydrogen. The effects of 

 bombarding a platinum surface by electrons the velo- 

 city of which could be gradually increased have been 

 investigated by methods in which these effects were 

 detected when superposed on thS original electron cur- 

 rent, and also when they were measured independently. 

 It has been found that a genuine ionisation by electron 

 impacts is produced at a minimum electron velocity 

 of 13-0 volts, but that up to electron velocities of 

 (30 volts no detectable amount of radiation capable of 

 acting photo-electrically on platinum is obtained. In 

 order to ascertain whether the ionisation produced at 

 a minimum electron velocity of 13-0 volts arises from 

 the platinum or from hydrogen attached to its surface, 

 the elTects of electron collisions with hydrogen were 

 investigated in the same apparatus. A radiation was 

 detected from this gas at a minimum electron velocity 

 of 105 volts, and a second type of radiation at a 

 minimum electron velocity of 139 volts. Three tvpes 

 of ionisation were also detected, beginning when the 

 electrons acquired velocities of 13-0 volts, 14-4 volts, 

 and_i6() volts respectively. The first of these tvpes is 

 the ionisation obtained in a high vacuum, and experi- 

 ments described in the paper show that this is not due 

 to hydrogen, but arises from the platinum itself. From 

 the experiments in hydrogen it is concluded that the 

 rninimum electron velocity for the production of radia- 

 tion from a hydrogen atom is 105 volts, the minimum 

 electron velocity for ionisation of the atom 14-4 volts, 

 and the minimum electron velocitv for ionisation of 

 the molecule 169 volts. These results are in general 

 agreement with the deductions from Bohr's theory. 

 The second type of radiation, beginning at an electron 

 velocity of 130 volts, is attributed to the hydrogen 

 molecule.— L. Bairsfow, R. H. Fowler, and D. R. 

 Hartree : The pressure distribution on the head of a 

 shell moving at high velocities. This paper describes 

 a first attempt to measure the pressure distribution on 

 a body moving through a gns at velocities equal to or 

 greater than the velocity of sound a in the gas. The 

 body in question is a spinning shell, moving along its 

 axis of symmetry, and the gas, air. The pressure at 

 a given distance from the nose is communicated to a 

 chamber in the head of the shell, and deduced from 

 the time of burning a train of powder in this chamber, 

 which is a quantity that can be directly observed. By 

 a series of such observations the pressure at a given 

 point of the head is determined as a function of the 

 velocity ratio i;/a, where v is the velocitv of the shell 

 relative to the air. Curves are obtained showing the 

 variation of the pressure for values of via from 004 

 to 1-4, and for four different positions on the head of 

 the shell. 



Paris. 

 Academy of Sciences, December aq, igiq.— M. L^on 

 Guignard in the chair. — G. Bigourdan ; The work of 



Lalande and his pupils at the Mazarin College. 



H. Deslandres : Remarks on the constitution of the 

 atom and the properties of band spectra. Completing 



four earlier communications on the same subject 



P. Termler and G. Friedel : The foldings and drift 

 NO. 2623, VOL. 104] 



which have broken the Gard coal basin ; probably 

 .Alpine movements of Miocene age. — A. Blondel : 

 Graphical study of the working of audions with 

 resonating circuit as sensitised receivers or as 

 dampers. — C. Sauvageau : The parasitism of a red 

 alga, Polysiphonia fastigiata. — F. Carlson : A property 

 of polynomials of one variable. — M. Mesnager : Method 

 of determination of the internal strains existing in a 

 circular cylinder. The method employed by M. Portevin 

 in a recent communication on the same subject, due 

 to Heyn and Bauer, is faulty, as it only takes into 

 account the tensions parallel to the axis of the cylinder. 

 -An outline of a more exact method is given. — J. Amar : 

 A machine for cutting out brushes. This instrument 

 has been specially designed for use by the blind. — 

 E. Kohn-Abrest : Aluminium spontaneouslv oxidisable 

 in the air. M. Guillet has recently described some 

 aluminium alloys which undergo oxidation in the air. 

 Some years ago the author found that aluminium 

 could be volatilised in a vacuum at 1100° C, and the 

 portion remaining unvolatilised sometimes proved to 

 be spontaneously oxidisable. No satisfactorv ex- 

 planation of the phenomenon could be found. — 

 N. R. Dhar and G. Urbain : The polarisation 

 electromotive forces of iron in solutions of complex 

 salts. Relation between these electromotive forces 

 and the disappearance of the analytical characters of 

 ferric ions. Measurements are given for ferrous and 

 ferric salts, ferrocyanides, ferrioxalates, ferricyanides, 

 and nitro-prussides. — E. Wourtzel : The dissociation 

 constant of nitrogen peroxide. — L. Vallery : The esti- 

 mation of arsenic in tin and in tinned articles. The 

 arsenic is first separated by distillation as chloride and 

 reduced to colloidal arsenic, and determined in a 

 colorimeter. The determination of arsenic in tin by 

 Marsh's method is liable to serious error. — A. Meyer : 

 The estimation of thiophen in benzene. — A. Kling 

 and D. Florentin : The production of carbon monoxide 

 in flames of different gases. Carbon monoxide is 

 mainlv produced bv sudden cooling of the flame; the 

 amount is increased by contact with the mantle of an 

 incandescent burner. — M. Zeil : Correlations between 

 the Quaternary terraces, glacial recurrence, and 

 upward movements of the earth's crust. — J. Bourcart : 

 Cretacean and Lower Eocene formations and their 

 extension in central and southern .Albania. — Ph. 

 Glangeaud : The reconstitution of a long lake denres- 

 sion which during the Oligocene period occupied the 

 great coal cut of the Central Massif. — Ch. Pussenot : 

 Glacial recurrences later than the " N^owurmien " in the 

 massifs of the .Aiguille de Polset (Tarentaise), of Mont 

 Thabor, and of the -Aiguille de Scolette (Maurienne). — 

 W. Kilian and Ch. Pussenot : The age of the tufa- 

 bearing human remains at Villard de Bozel (Savoie). 

 — Ch. Maurain : The wind velocity in the stratosphere. 

 There is a maximum mean wind velocity (14-55 metres 

 per second) at a height of about 11,000 metres, 

 falling to S-04 metres per second at iq.ooo metres alti- 

 tude. — MM. Stapfer and Moleski : Remarks on snow- 

 falls. Two cases are considered, the first when the 

 snow has alreadv been formed in the northern regions 

 and the second when it is formed near where it falls. 

 The conditions existing on the occasion of the fall of 

 snow at Paris on November 3 are examined, and 

 found to confirm the views expressed in earlier com- 

 munications. — P. Carles : The blue ca'sse of wine. 

 Criticisms on a recent communication bv M. Piedallu. 

 — M. Gard : Biology of a new species of Euglaena 

 (E. limnsa). — L. Laplcqne : .Seasonal variation in the 

 chemical composition of marine algte. There is 'a 

 0reat variation in the amount of soluble carbohydrate 

 in Laminaria flexicaulis. These attain a maximum in 

 .August and September, and fall to a minimum at the 

 end of the winter. The changes in ash are in the 



