;.42 



NATURE 



[August i, 1907 



crcctiny a new boiler house and lavatories; is proposing 

 to extend the refectory ; is adapting a large dwelling house 

 for the purposes of an extension of the geological depart- 

 ment, and is uniting the house by means of a bridge at 

 the first-story level with the present geological department 

 of the University ; and is adapting other dwelling houses 

 for the use of women students and for seminar work. 



The second International Congress on School Hygiene 

 will be opened on August 5, at the request of the King, 

 by Lord Crewe. The complete success of the meetings 

 seems to be assured. The German Government has not 

 only decided to send delegates to the congress, but, bv 

 permission of the Kaiser, Prince Kite! Friedrich has 

 accepted the office of a vice-patron of the congress. While 

 still adhering to its resolution not to issue official invita- 

 tions to foreign Governments to send delegates, the Board 

 of Education has arranged with the Foreign Office to 

 take such steps as are likely to remove any misunder- 

 standing which might have prevented some foreign 

 delegates from accepting the invitations issued. The 

 meetings will be held at the Universilv of London, and 

 will last until August 10. Sir Lauder" Brunton, F.R.S., 

 the president, will deliver the inaugural address on 

 August 5. The sectional meetings will commence on the 

 foliott'ing day. There are eleven sections in all ; their 

 subjects and the name of the president in each case are 

 as follows : — (i) The physiology and psychology of educa- 

 tional methods and work. Sir James Crichton Browne, 

 F.R.S. ; (2) medical and hygienic inspection in school. 

 Prof. W. Osier, F.R.S. ; (3)' the hygiene of the teaching 

 profession. Dr. T. J. Macnamara, M.P. ; (4) instruction 

 in hygiene for teachers and scholars. Sir William J. 

 Collins, ^^P. ; (5) physical education and training in 

 personal hygiene, Sir John W. Bycrs ; (6) out-of-school 

 hygiene, holidav camps and schools : the relation of home 

 and the school. Lord Kinnaird ; (7) contagious diseases, 

 ill-health, and other conditions affecting attendance. Sir 

 Shirley F. Murphv ; (S) special schools for feeble-minded 

 and exceptional children. Mr. W. H. Dickinson, M.P. ; 

 fq) special schools for blind, deaf and dumb children. 

 Lord Crewe: (10) hygiene of residential schools. Dr. 

 Clement Dukes; ('ii') the school building and its equip- 

 ment, Mr. T. E. Colcutt. An exhibition" of school build- 

 ing and furnishing appliances has been arranged in 

 connection with Ae congress. "" 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, June 6. — "On the Two Modes of Con- 

 densation of Water Vapour on Glass Surfaces, and on 

 their Analogy with James Thomson's Curve of Transition 

 from Gas to Liquid." By Prof. Fred. T. Trouton, F.R.S. 



Experiments made with glass wool to determine the 

 amount of w^ater condensed on the surface of glass when in 

 equilibrium with various vapour pressures showed thai 

 below a critical pressure, w^hich is about 50 per cent, 

 saturation, there are two distinct modes in which the 

 condensed water can exist. 



Thus for the same vapour pressure, if the condensation 

 is in one of these forms, called for convenience the a type, 

 there is much less condensed material present on the surface 

 than in the other form, called the $ type; or, to put it in 

 another way, for the same amount of condensed vapour 

 the pressure is greater when the condensation is of the 

 a form than when it is of the B form. 



Condensation will take place of the a type if the surface 

 has been thoroughly dried at high temperatures, while of 

 the B type if the drying has only been effected at ordinary 

 temperatures, though in that case also the vapour pressure 

 may be zero. 



When the condensation is of the $ type the curve, con- 

 necting pressure with the amount of condensed water, Ik 

 found to be very similar to that for wool or cotton, but 

 yvhen the condensation is of the o tvpe the curve is quite 

 dilTerent. Thus, starting with the surface very dry, the 

 pressure runs up quickly for relatively little condensation 

 NO. 1970. VOL. 76] 



until a critical pressure is reached ; after that, on further 

 additions to the surface condensation, the pressure 

 diminishes. This is attributed to a transformation into the 

 B state supervening at this point, when consequently thp 

 vapour pressure 'is in excess of equilibrium, and thus a 

 depiction of the vapour in the surrounding space results, 

 with a corresponding fall in vapour pressure. If moisture 

 be continuously supplied the pressure will, after reaching a 

 maximum, begin to rise, and ultimately pass to saturation. 



The analogy with James Thomson's curve of transition 

 from gas to liquid is pointed out. In the one case there 

 is attraction between waler-vapour particle and water- 

 vapour particle, in the other between glass and water 

 vapour. The condensation of the a type corresponds to 

 the supersaturated vapour stage in the transition curve, 

 while the 6 corresponds to its liquid stage. 



Where the surface is not completely dry, the fact that 

 the condensation is in the B form, on vapour coming in 

 contact with the surface, is attributed to there being art 

 example of that type already on the surface ; but if this is 

 not present, that is, if the surface is desiccated, the con- 

 densation is of a type allied to supersaturated vapour 

 rather than to the liquid. 



A paradoxical consequence of there being these two 

 modes of condensation is pointed out, namely, that a 

 relatively wet surface is capable of drying one wetter than 

 itself. 



As an illustration of the phenomenon a simple experiment 

 is given, in which two di.shes of phosphorus pentoxide ara 

 placed undei- a bell jar, with only this difference, that one 

 of the dishes is first made dry by heating. It is then found 

 that the pentoxide which can initially obtain some 

 moisture from contact WNth the damp dish absorbs the 

 moisture in the bell jar, and ultimately runs liquid, while 

 the other remains dry. 



" On the Wlocity of Rotation of the Electric Dis 

 charge in Gases at Low Pressures in a Radial Mag- 

 netic Field." By Prof. H. A. Wilson, F.R.S., and 0. H. 

 Martyn. 



The apparatus used in this investigation was a smalt 

 vacuum tube consisting of two concentric glass tubes 

 cemented into aluminium discs. The discs served as elec- 

 trodes, and the discharge was passed between them through 

 the annular space between the glass tubes. 



An iron bar was fixed along the axis of the vacuum 

 lube, and could be magnetised so as to produce a radial 

 field in the space between the glass tubes. 



The discharge was produced by a large secondary battery, 

 and its velocity of rotation round the annular space was 

 measured. The variation of the velocity with the strength 

 of the magnetic field, with the pressure of the gas, and 

 with the current carried by the discharge, was investigated 

 in air, nitrogen, and hydrogen. 



The velocity was found to be nearly proportional to the 

 strength of the magnetic field and inversely proportional 

 to the gas pressure. The velocity in hydrogen was about 

 thirteen times the velocity in air or nitrogen. 



It is shown that theoretically the velocity should be pro- 

 portional to the product of the two ionic velocities, and 

 the results obtained, together with previous measurements 

 of the Hall effect, enable the velocities of both the positive 

 and negative ions to be calculated. The negative ions are 

 found to have much higher velocities than the positive). 



June 13. — " liliadesmia memhraimcca, Bertrand ; a New 

 Palneozoic Lycopod with a Seed-like Structure." By Dr. 

 M. Benson. Communicated by Dr. D. H. Scott, F.R.S. 



The vegetative organs of this interesting new type w-ere 

 discovered by Bertrand in iSqd. He found them in sections 

 of a calcite nodule from the Gannister beds of Hough Hill, 

 England. .A large quantity of new material has become 

 .available, and now not only are more details known as to 

 the vegetative organs, but a fairly complete knowledge of 

 the reproductive organs is possible. 



Miadesmia was exceedingly minute, its stem slender 

 and without any trace of skeletal tissue. It is the first 

 Palaeozoic Lycopod of herbaceous character known struc- 

 turally. The megasporophylls, which were identified by 

 Dr. D. H. Scott, F.R.S., in 1901, show a more advanced 



