590 



SCIENCE. 



[N. S. Vol. XI. No. 276. 



plain that the year is by far the more important 

 of the two. The only inconvenience that could 

 arise from not knowing the volume would be 

 that in the case of those journals in which the 

 volume does not begin with the year it might 

 sometimes be necessary to take down from the 

 shelf two books instead of one before the right 

 place is found — an inconvenience of the very 

 slightest kind. Of course every really virtuous 

 scientific writer now gives his full references at 

 the end of his paper, with year and volume 

 both, and refers to them in the body of his 

 paper thus — Dejerine-Klumpke, '94, III. — 

 when the reference is to the third paper issued 

 by Dejerine-Klumpke in the year 1894. Pend- 

 ing the attainment of perfect virtue on the part 

 of writers (and also for the convenient reading 

 of all articles of the past), I submit that a table 

 of cross-references, such as I have described, 

 would be a work deserving of heartfelt gratitude 

 on the part of an overworked scientific world. 



C. L. F. 



[A chronological table giving the year in 

 which each volume of 550 scientific journals 

 was published is included in the 'Catalogue of 

 Scientific and Technical Periodicals,' by Dr. H. 

 Carrington Bolton, the second edition of which 

 was published by the Smithsonian Institution in 

 1897.— Ed. Science.] 



the international congress of mechanics. 

 To THE Editor op Science : M. Marcel 

 Delmas, 10 Boulevard Emile Augier, Paris- 

 Passy, has charge of the report of the ' Congress 

 de Mecanique de I'Exposition universelle,' in 

 the department of applications of electricity to 

 the various apparatus of haulage, hoisting, etc. 

 (including cranes, elevators, winches, swing- 

 bridges, pumps and other such mechanisms), 

 and particularly desires information regarding 

 the economic side of the matter. He requests 

 that all, whether intending exhibitors or others, 

 who are willing to assist in the collection of this 

 data, send him, at the address given above, 

 statements of costs of installations, of exploita- 

 tion and incidental expenses, especially where 

 a comparison can be made with costs of the 

 older systems under similar circumstances. All 

 publications and illustrations will be welcome. 



if authentic and exact in statementof facts and 

 data. 



R. H. Thurston. 



NOTES ON PHYSICS. 

 LIQUID AIR. 



C. LiNDE gives some interesting data on liquid 

 air in the Physikalische Zeitschrift for January 

 6, 1900. He calls attention to the fact that the 

 commercial use of liquid air depends in the first 

 place upon the amount of energy consumed in 

 its production and upon the length of time that 

 the liquid can be kept before it is used. With 

 small machines from 3 to 4 horsepower — hours 

 are used per kilogram of liquid air, while the 

 largest machine hitherto built, produces fifty 

 kilograms of liquid air per hour and consumes 

 about 100 H. P. This latter corresponds to an 

 efiiciency of 15 fo as compared with what a per- 

 fect thermodynamic machine would accomplish. 



Small quantities (about one liter) of liquid 

 air in vacuum jacketed and silvered vessels are 

 lost by evaporation in about 14 days. In large 

 tin vessels (50 liters) covered with hair felt 

 about two liters per hour is lost by vaporization. 

 The author gives data concerning the use of 

 liquid air for refrigeration and for power. 

 When extremely low temperatures are desired 

 liquid air is perhaps the best possible means for 

 producing it. On the other hand from twenty 

 to forty times as much energy is consumed in 

 producing moderate refrigeration by liquid air 

 than is required in the ordinary ammonia re- 

 frigerator. Thus a kilogram of liquid air evap- 

 orated in a room reduces the temperature of the 

 room only about as much as the melting of two 

 kilograms of ice, and two kilograms of ice may 

 be produced by the evaporation of 1/20 horse- 

 power-hour or less. 



When liquid air as evaporated at ordinary 

 temperatures and used to drive a motor, the 

 work developed by the motor is only about 

 three or four per cent, of the energy consumed 

 in the production of the liquid air. The author 

 however points out special cases where the use 

 of liquid air for power might be desirable. 



The author mentions some experiments which 

 have been made in the Simplon tunnel, now 

 building, to test the usefulness of a mixture'of 

 liquid air or liquid oxygen and mineral oil 



