MODERN SCIENCE. 257 



of gases have (in January, 1893) been supplemented by 

 the beautiful discovery of Prof. Dewar, who succeeded in 

 LIQUEFYING AIR ITSELF, as distinguished from its con- 

 stituents. This result was obtained by getting a vacuum 

 approaching a point vastly nearer the ideal vacuum than 

 had ever been obtained before, since exhausted vessels con- 

 tain less than the Qoopooth of the air which the best air- 

 pumps of thirty years ago left in them. This almost perfect 

 vacuum is, he found, an absolute barrier to the passage of 

 heat rays, and allows the liquid air to remain permanently 

 in its vacuum envelope. Should verification permit the 

 formulation of a new law, this law, it is surmised, would 

 lead to a revision of some of our astronomical conclusions. 

 These discoveries, it is almost needless to add, imply the 

 highest skill in investigation, not to speak of an adequate 

 command of means. 



b. 1 8 . Faure invented the ELECTRIC ACCUMULATOR 

 a new and fruitful apparatus for storing power, which makes 

 the electric train or car an inexpensive possibility. 



1832 1 8 . Kirk invented an ICE MACHINE depending 

 upon the cold produced by the expansion (or rarefaction) 

 of air gas compression causing a rise, and expansion a 

 decrease, of temperature (because a quantity of sensible heat 

 disappears when a gas increases in volume). This law 

 explains the cold produced by nocturnal radiation. In 

 Bengal the nocturnal cooling is used in manufacturing ice. 

 " Large flat vessels containing water are placed on non- 

 conducting substances such as straw or dry leaves." In 

 consequence of the radiation the water freezes, even when the 

 temperature of the air is ten degrees Centigrade. 



b. 1832. Crookes invented a SPECTRUM MICROSCOPE 

 which overcomes some of the difficulties due to slightness 

 of light dispersion; discovered (1861) Thallium with the 

 spectroscope the third metal found by that means; in- 

 vented the RADIOMETER (April, 1875), b y means of which 

 he claimed to have discovered and proved light to be a 

 motive power a conclusion which, however, has not found 

 general acceptance, for it is suggested that the mechanical 

 action seen in the instrument is probably due to the more 



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