November 6, 19 19] 



NATURE 



247 



rated. The main asset of both the aeroplane and 

 the airship is speed, and here the importance of 

 long distances will be evident on little considera- 

 tion. In a country like England, with well- 

 organised railway trunk lines and journeys of the 

 order of 500 miles, the saving of time in the 

 carriage of mails is small, particularly since the 

 mail trains travel by night, whereas aeroplanes 

 wait for the dawn before commencing the journey. 

 Where the route includes a sea passage the 

 advantages are much greater, and the enterprise 

 of our two leading transport companies has shown 

 the possibility of a remarkable degree of certainty 

 in the service between London and Paris. It is, 

 however, on much longer journeys than these that 



the saving of time by aerial transport presents its 

 most attractive possibilities. 



On the other hand, the initial outlay and run- 

 ning expenses are roughly proportional to the 

 length of journey, and the inception therefore 

 represents a formidable undertaking. The returns 

 are problematical, and from the nature of the case 

 it will be obvious that until the special facilities 

 have existed for some time no estimate of value 

 can be made as to the charges which will prove 

 remunerative to an operating company and suffi- 

 ciently attractive to the users of the new form of 

 transport. 



Civil aerial transport is therefore still in its 

 infancy as an addition to our industrial life. 



THE LIQUEFACTION OF GASES. 



By Prof. C. H. Lees, F.R.S. 



T N 1869, when the first number of Nature ap- 

 *- peared, Andrews had just completed his 

 experiments on carbonic acid, and established the 

 fact that for each gas there is a critical tem- 

 perature above which it is impossible to liquefy 

 the^as by pressure. Faraday, by using low tem- 

 peratures and considerable pressures, had liquefied 

 chlorine^ sulphurous and hydrochloric acids, 

 cyanogen, and ammonia in 1823, by 1844 had added 

 eight other gases to the list, and had solidified 

 sulphuretted hydrogen, ammonia, and nitrous 

 oxide. Cailletet, in 1878, by suddenly reducing 

 the pressure on oxygen, nitrogen, and carbonic 

 oxide compressed to 300 atmospheres, obtained 

 mists which he ascribed to fine drops of the lique- 

 fied gas. Pictet, about the same time, by employ- 

 ing greater pressures and cooling his apparatus 

 with other liquefied gases, succeeded in obtaining 

 a small quantity of liquid oxygen which was of a 

 slightly blue colour. 



In 1883, at Cracow, Wroblewski and Olszewski 

 succeeded in obtaining small quantities of liquid 

 oxygen, nitrogen, and air, which evaporated in a 

 few seconds. By 1887 Olszewski could obtain a 

 few c.c, and by igoo 100 c.c, of liquid oxygen 

 before an audience of his students. Dewar had 

 been able to produce quantities exceeding 20 c.c. 

 since 1886, and had already made determinations 

 of the properties of substances at the low tempera- 



tures thus attainable. In 1892 he introduced the 

 double-walled vacuum vessels with a little mercury 

 within to convert the internal surfaces into mirrors, 

 now known as Dewar flasks. These reduced the 

 rate of evaporation of a liquid gas stored in them 

 to about a thirtieth of the rate for ordinary vessels. 

 The utilisation of the Joule-Kelvin cooling effect 

 by Linde and by Hampson in 1895 enabled each 

 to produce a machine capable of liquefying air, 

 oxygen, and nitrogen on a commercial scale. In 

 1898 Dewar produced for the first time liquid 

 hydrogen, using the Joule-Kelvin effect in the gas 

 pre-cooled to 68° A. by a bath of liquid air 

 evaporating in vacuo. Next year he solidified it, 

 and determined its melting point to be 14° A. In 

 1908, at Leyden, Kamerlingh Onnes liquefied 

 helium and determined its boiling point to be 4° A. 

 In the meantime, Olszewski had liquefied and 

 solidified argon in 1895, and Ramsay and Travers 

 had by 1900 liquefied krypton and xenon. 



The commercial production of liquefied gases 

 gave facilities for the examination of the physical 

 properties of substances at low temperatures, and 

 in this work Dewar and Kamerlingh Onnes and 

 his pupils have played prominent parts. It is to 

 the Leyden professor we owe the discovery of 

 the disappearance of the electrical resistances of 

 many metals at temperatures a few degrees above 

 absolute zero attained by the use of liquid helium. 



PROGRESS OF METEOROLOGY. 



By W. H. Dines, F.R.S 



'"T^HE progress of meteorology during the last 

 -•- fifty years has been very marked, as may 



astronomy as an exact science from the old 



astrology, but it must be confessed that the 



be seen by a casual reference to the current ! Newton of meteorology has not yet appeared. 



meteorological literature of the period 1865-75 ; , Fifty years back the student of meteorology 



to a great extent, it resembles the emergence of spent much of his time in a vain hunt for weather 



NO. 2610, VOL. 104] 



