104 



THE POPULAR SCIENCE MONTHLY 



low temperatures, by which Ormes was 

 enabled to maintain and control the 

 temperature ranges from — 23° to 



— 90° (methyl chloride), from — 105° 

 to —165° (ethylene), and —183° to 



— 217° (oxygen). This goal may be 

 said to have been attained about 1894. 

 The second stage was characterized by 

 the introduction of liquid hydrogen and 

 the production of temperatures below 



— 217°. The abnormal behavior of hy- 

 drogen gas when it is allowed to ex- 

 pand under reduced pressures made it 

 impossible to liquefy it at higher tem- 

 peratures; and the condensation of this 

 gas was first achieved by Dewar, of 

 London, on May 10, 1898. This added 

 a new range of available low tempera- 

 tures from — 253° to — 250° in which 

 Dewar made a number of highly re- 

 markable observations, including the 

 solidification of hydrogen. But Onnes 

 very promptly appropriated this new 

 range for his research work, and con- 

 structed novel and very efficient appa- 

 ratus for the production and utilization 

 of the new refrigerant. 



The Netherlands government, realiz- 

 ing the importance of the work, now 

 granted considerable appropriations for 

 the extension and equipment of the lab- 

 oratory, and with its completion a new 

 era of constantly increasing low tem- 

 perature research began. New methods 

 and instruments for the exact measure- 

 ment of temperatures below the boil- 

 ing-point of liquid hydrogen were de- 

 vised, and the behavior of mixtures of 

 hydrogen and helium was systematically 

 investigated. Finally, the apparently 

 incoereible gas, helium, was reduced to 

 the liquid state. This crowning tri- 

 umph of low temperature research 

 was achieved on July 10, 1908. This 

 achievement aroused universal interest 

 in the work of Onnes and doubtless 

 j>rompted the award to him, in 1913, of 

 the Nobel Prize in Physics. 



During the past few years Onnes has 

 made some most remarkable discoveries 

 with reference to the electrical resist- 

 ance of certain metals at temperatures 



zero of temperature. The resistance of 

 metals ordinarily varies approximately 

 with the absolute temperature, but at 

 temperatures only a few degrees above 

 the absolute zero it suddenly becomes so 

 small that it can hardly be measured. 

 For mercury this "critical tempera- 

 ture" is 4.2° absolute; for lead it is 

 6.1°, and for tin 3.8°. Below these 

 temperatures the resistance is prac- 

 tically nil, and Onnes terms this the 

 "supraconductive " state. In this state 

 the metals no longer obey Ohm 's law — 

 there is neither a potential drop nor a 

 production of heat. 



SCIENTIFIC ITEMS 



We record with regret the deaths of 

 Joseph Johnston Hardy, professor of 

 mathematics and astronomy at La- 

 fayette College; of Dr. Samuel Bald- 

 win Ward, since 1884 dean of the Al- 

 bany Medical College and professor of 

 the theory and practise of medicine, 

 and of James Blaine Miller, of the 

 Coast and Geodetic Survey, a passenger 

 on the Lusiianiii. 



The Barnard gold medal awarded 

 every fifth year by Columbia Univer- 

 sity, on the recommendation of the Na- 

 tional Academy of Sciences, "to that 

 person who, within the five years next 

 preceding, made such discovery in phys- 

 ical or astronomical science, or such 

 novel application of science to purposes 

 beneficial to the human race, as may 1 e 

 deemed by the National Academy of 

 Sciences most worthy of the honor," 

 will be given this year to William IT. 

 Bragg, D.Sc, F.R.S., Cavendish pro- 

 fessor of physics in the University of 

 Leeds, and to his son, W. L. Bragg, of 

 the University of Cambridge, for their 

 researches in molecular physics and in 

 the particular field of radio-activity. 

 The previous awards of the Barnard 

 medal have been made as follows : 

 1895 — Lord Rayleigh and Professor 

 William Ramsay; 1900 — Professor Wil- 

 helm Conrad von Ri'mtgen ; 1905 — Pro- 

 fessor Henri Becquerel; 1910— Pro- 



only a few degrees above the absolute fessor Ernest Rutherford. 



