NA TURE 



[July 6, 1905 



The " Bubbling" Method and Vapour Pressures. 



In the course of an endeavour to determine the osmotic 

 pressure of a solution by measuring the relative lowering 

 of its vapour pressure, we have been led to abandon 

 Oswald and Walker's bubbling method on account of its 

 inherent inaccuracy. 



As the disabilities of this method seem to have been 

 overlooked, we think that this note may be of use to 

 other worlcers in the same field. 



Oswald and Walker, it will be remembered, bubbled 

 dry air through the solution, then through the water, and 

 absorbed the moisture by means of sulphuric acid. The 

 loss of weight of the water measures the relative lower- 

 ing of the vapour pressure of the solution, and the gain 

 in weight of the sulphuric acid represents the vapour 

 pressure of the pure solvent, water. 



Assuming the air to be at the same temperature through- 

 out, it can easily be seen that the space occupied by a 

 bubble of air, when leaving the solution, will be less than 

 that which the same bubble will occupy when leaving the 

 water, that is, the bubble expands while travelling up the 

 water column, and will have taken up more water vapour 

 than it should. The e.xpansion of the bubble (and con- 

 sequently the amount of vapour necessary to saturate the 

 space occupied by it) is proportional to the difference in 

 pressure at the top and bottom of the water column. If 

 the total depth of the latter be, say, 6 inches,- and the 

 barometer stand at 30 feet of water, then an error of 

 I part in 60 is induced. 



This can conveniently be verified by passing air through 

 two or more WinKler's tubes filled with water; it will 

 always be found that the e,xit tube has lost weight. 

 Owing to the form of the equation connecting osmotic and 

 vapour pressures, the effect of the above error is magnified. 

 Berkeley. 



Fo.xcombe, near Oxford. E. G. J. Hartley. 



Luminosity and Colour. 



In conjunction with my other methods of testing colour 

 vision, I have been using Rayleigh's apparatus for match- 

 ing yellow with a mi.xture of spectral red and green. I 

 find that the proportions of red and, green depend upon 

 the luminosity of fhe match (both the mixed colour and 

 the simple one being of similar luminositv) ; for instance, 

 I require two and a half times as much green in the 

 mi.xed colour when the match is bright compared with a 

 match at a lower luminosity. Some persons make a match 

 which is nearly the same at several luminosities, others 

 require more and more green as the luminosity is 

 diminished, and others when the luminositv is diminished 

 cannot make a match at all. So three 'normal sighted 

 persons may make a similar match at one luminosity, and 

 at another one may appear to be an anomalous trichro- 

 matic and the other colour blind. I find that a colour 

 blind person (a dichromic with considerable shortening of 

 the red end of the spectrum) may make a match like a 

 normal sighted one. F. W. Edridge-Green. 



St. John's College, Cambridge. 



MEETING OF THE BRITISH ASSOCIATION 



IN SOUTH AFRICA. 

 "T^HE arrangements for the forthcomings meeting- of 

 •*- the British Association in South Africa have now 

 been completed, and Mr. Silva White, the assistant 

 secretary of the association, sailed for Cape Town in 

 the W aimer Castle on Saturday last, July i. The 

 number of members who will proceed to South Africa 

 to attend the meeting is 385, and of these no less 

 than 276 members have intimated their intention to 

 visit the Victoria Falls at the conclusion of the 

 ordinary work of the association. The official party, 

 consisting of leading representatives of science aiid 

 guests of the association, with the general and 

 sectional officers for this meeting and the president, 

 numbers 140 in all, and will sail by the Saxon on 

 July 29. Most of the other members will proceed to 

 the meeting by the Durham Castle and the Kildonan 

 Castle, both of which sail on July 22. 

 NO. 1862, VOL. 72] 



In a previous article (May 18, p. 59) the local 

 arrangements for the meeting were described. There 

 will be receptions and social functions, excursions, 

 &c., at Cape Town, Durban, Pieterniaritzburg, 

 Johannesburg, Klmberley, and Bulawayo. The central 

 organising committee for South Africa (chairman, 

 Sir David Gill, K.C.B., F.R.S., hon. secretary. Dr. 

 Gilchrist) has carried out the coordinating work of 

 the programme. The lists of local committees and 

 subcommittees contain nearly one thousand names, 

 from which it may be concluded that much interest 

 is taken in the meeting. 



As already mentioned, lectures of a popular 

 character will be delivered at the chief towns visited. 

 These lectures have now been definitely arranged as 

 follows : — 



Cape Town : \V. J. Burchell's discoveries in South 

 .■\frica. Prof. Poulton ; some surface actions of fluids, 

 Mr. C. V. Boys. Durban : Mountains : the highest 

 Himalaya, Mr. D. Freshfield. Pieterniaritzburg: 

 Sleeping-sickness, Colonel D. Bruce. Johannesburg : 

 Distribution of power. Prof. Ayrton ; steel as an 

 igneous rock. Prof. .-Xrnold. Pretoria: Fly-borne 

 diseases, malaria, sleeping-sickness, &c., Mr. A. E. 

 Shipley. Bloemfontein : The Milky Way and the 

 clouds of Magellan, Mr. A. R. Hinks. Kimberley : 

 Diamonds, Sir William Crookes ; bearing of engineer- 

 ing on mining. Prof. Porter. Bulawayo : Zimbabwe, 

 Mr. Randall-Maclver. 



The president's address to the association will be 

 delivered at Cape Town on August 15, and at 

 Johannesburg on August 30. Mr. G. W. Lamplugh's 

 report on the geology of the Victoria Falls will take 

 the form of an afternoon address to Section C at 

 Johannesburg. 



Subjoined is a draft programme of the work of the 

 sections : — 



Section A (Mathematics and Physics). — Cape Town : 

 President's address ; progress of the arc of meridian and 

 geodetic survey of South Africa, Sir D. Gill ; to what 

 extent can the ether affect the motion of matter? Prof. J. 

 Larmor ; observations of atmospheric electricity in South 

 Africa, Prof. Beattie and Mr. Lyie ; leak of electricity 

 from certain heated substances. Prof. Beattie ; the found- 

 ations of the kinetic theory of gases, Mr. Burbury ; appli- 

 cation of the kinetic theory of nebulse, Mr. J. H. Jeans; 

 radiation at low temperatures. Dr. J. T. Bottomley. There 

 will also probably be communications from Mr. Hough on 

 tides, and from Dr. Roberts on the Algol variables. 

 Johannesburg : On the teaching of elementary mechanics 

 (jointly with Section L if possible). Prof. J. Perry; on 

 flight, Prof. G. H. Bryan ; (i) electrical conductivity in 

 relation to chemical action ; (2) magnetic survey of South 

 .'\frica. Prof. Beattie ; report of the seismological com- 

 mittee, Prof. J. Milne ; a form of dry Daniell cell, Mr. J. 

 Brown ; the strength of winding ropes in mines, Prof. 

 Perry ; the experimental foundations of the theory of heai 

 conduction, Dr. C. H. Lees. There will probably be a 

 communication from Mr. Sutton on the meteorology o( 

 South Africa. 



Section B (Chemistry). — Detailed information regarding 

 papers offered by members in South Africa has not yet 

 been received, but the following provisional arrangement 

 has been made : — Cape Town : Recent advances in agri- 

 cultural science, A. D. Hall ; vegetable assimilation. Dr. 

 Horace T. Brown ; enzyme action, Dr. E. F. Armstrong. 

 These communications are intended to serve as a basis of 

 discussion of agricultural chemical problems. Johannes- 

 burg: President's address; reports on various aspects of 

 the metallurgy of gold by local experts. Communications 

 by Dr. H. Marshall on the experimental basis of the 

 dissociation hypothesis, and by H. Ingle on the soils of 

 the Transvaal, have been provisionally accepted. 



Section C (Geology). — Cape Town : Opening remarks bv 

 the president ; the continent of Africa in relation to the 

 physical history of the earth, Prof. \V. J. Sollas ; the 

 classification of the Karroo beds of South .Africa, Prof. R. 

 Broom ; report of the committee on the fauna and flora 



