For further information the reader may consult W. L. Hardin, _Rise and Development of the Liquefaction of Gases_ (New York, 1899), and Lefèvre, _La Liquéfaction des gaz et ses applications_; also the article CONDENSATION OF GASES. But the literature of liquid gases is mostly contained in scientific periodicals and the proceedings of learned societies. Papers by Wroblewski and Olszewski on the liquefaction of oxygen and nitrogen may be found in the _Comptes rendus_, vols, xcvi.-cii., and there are important memoirs by the former on the relations between the gaseous and liquid states and on the compressibility of hydrogen in _Wien. Akad. Sitzber._ vols. xciv. and xcvii.; his pamphlet _Comme l'air a été liquéfié_ (Paris, 1885) should also be referred to. For Dewar's work, see _Proc. Roy. Inst._ from 1878 onwards, including "Solid Hydrogen" (1900); "Liquid Hydrogen Calorimetry" (1904); "New Low Temperature Phenomena" (1905); "Liquid Air and Charcoal at Low Temperatures" (1906); "Studies in High Vacua and Helium at Low Temperatures" (1907); also "The Nadir of Temperature and Allied Problems" (Bakerian Lecture), _Proc. Roy. Soc._ (1901), and the Presidential Address to the British Association (1902). The researches of Fleming and Dewar on the electrical and magnetic properties of substances at low temperatures are described in _Proc. Roy. Soc._ vol. lx., and _Proc. Roy. Inst._ (1896); see also "Electrical Resistance of Pure Metals, Alloys and Non-Metals at the Boiling-point of Oxygen," _Phil. Mag._ vol. xxxiv. (1892); "Electrical Resistance of Metals and Alloys at Temperatures approaching the Absolute Zero," _ibid._ vol. xxxvi. (1893); "Thermoelectric Powers of Metals and Alloys between the Temperatures of the Boiling-point of Water and the Boiling-point of Liquid Air," _ibid._ vol. xl. (1895); and papers on the dielectric constants of various substances at low temperatures in _Proc. Roy. Soc._ vols. lxi. and lxii. Optical and spectroscopic work by Liveing and Dewar on liquid gases is described in _Phil. Mag._ vols. xxxiv. (1892), xxxvi. (1893), xxxviii. (1894) and xl. (1895); for papers by the same authors on the separation and spectroscopic examination of the most volatile and least volatile constituents of atmospheric air, see _Proc. Roy. Soc._ vols. lxiv., lxvii. and lxviii. An account of the influence of very low temperatures on the germinative power of seeds is given by H. T. Brown and F. Escombe in _Proc. Roy. Soc._ vol. lxii., and by Sir W. Thiselton Dyer, _ibid._ vol. lxv., and their effect on bacteria is discussed by A. Macfadyen, _ibid._ vols. lxvi. and lxxi. (J. Dr.) FOOTNOTES: [1] Figs. 1, 5, 6, 7, 10, 11, 12, 13 in this article are from _Proc. Roy. Inst._, by permission.