TRANSACTIONS OF SECTION A. 537 



4. The work of Amagat and Young has sufficiently indicated the general 

 course of the isothermals and their general correspondence. Work is now wanted 

 •which is sufficiently accurate and extended to show the differences from the law 

 shown by various groups of substances. For many problems an accuracy of tttVit 

 at least is required, and this can only be attained by the greatest care in the 

 measurement of pressure volume and temperature. Such has been the object and 

 the result of the work carried on at Leiden for some years. 



The isotherms of argon would enable many problems to be attacked owing 

 to the probable physical constancy of the molecule, and would form standard 

 isothermals. Present results are rarely standard, as they usually depend upon 

 the readings of a gas manometer filled with air or nitrogen, and thus are in- 

 fluenced by the imcertainty in the isotherms of these gases. The only really 

 accurate isotherms at present known are those of hydrogen and oxygen, of 

 which gases the latter is unsuitable for standard instruments. A systematic 

 use of the hydrogen manometer at a standard temperature would obviate the 

 difficulty. 



Starting from the hydrogen isotherm ' at 20° C. as standard, the isotherms of 

 oxygen at pressures up to 60 ats. and at temperatures between 20° and — 120° C. 

 have been studied, and the isotherms at 20°, 15-6°, 0-0° published.'- The other 

 isotherms will shortly be given, together with very accurate determinations of the 

 critical constants, which will make possible an accurate equation of four terms 

 for oxygen. The other data rt;quired to completely check the differences in the 

 general equation are not to hand, except the compressibilities of hydrogen ^ at a 

 few pressures and at temperatures between 0'0° and —196° C, where hydrogen 

 corresponds to oxygen between 0-0° and 100"0° C, and hence where the minimum 

 of pv can be found experimentally. The numbers allow the value of f8 to be 

 fairly accurately fixed. 



4. On the Graphical Re2Jresentation of Ramsay aiid Young's Law for the 

 Comparison of Vapours at Equal Pressures. By Professor J. D. 

 Everett, F.R.S. 



5. Dependence of Pitch of Minute Closed Pipes on Wind Pressure.^ 

 By a S. Myers, 3LJ). 



The author gave a preliminary account of recent experiments on the varying 

 pitch of tones produced from Galton whistles according to the wind pressure 

 employed. He showed that for every pipe-length there is an optimum wind 

 pressure for the production of the highest tone ; that under certain conditions 

 the pressure can be so adjusted as to give no audible sound, while a note can j'et 

 be heard if the pressure is in the least degree increased above or diminished below 

 that point ; and that, under other conditions, increase of wind pressure may 

 produce a sudden decrease instead of the more common rise of pitch. 



G. A Lens for Ultra-violet Therapy. By J. William Gifford. 



Reference is made to a photographic doublet of quartz and calcite described at 

 the Bradford Meeting in 1900, and a triple achromatised similarly for the chemical 

 and visual maxima (wave-lengths 2748 and 5607) is recommended for the 

 purpose. 



The chief requirements are — 



1. That the calcite lens be protected. 



' Schalkwijk, Communications, Leiden, No. 70. 



■■' Onnes and Hyndman, ibid., Leiden, Nos. 69 and 78. 



' Ibid., Leiden, No. 82, January 1903. 



■" Full data are given in Journ. of Physiol., vol. xxviii., No. 6, 1902. 



