166 



SCIENCE, 



[N. S. Vol. IV. No. 84. 



Times, the lecturer showed that the conductiv- 

 ity of a pure iron wire, at ordinary tempera- 

 tures only about one-sixth of that possessed by 

 a copper wire of equal size, was increased nine 

 or ten times under the influence of the cold of 

 liquid air. But while pure metals had their 

 conductivity immensely increased by intense 

 cold it was shown that alloys, such as brass or 

 German silver, experienced in the same circum- 

 stances a comparatively small increase in con- 

 ducting power, not more than about ten per 

 cent. By carefully examining with a suitable 

 form of resistance coil the variations in the 

 electric resistance of a large number of chemi- 

 cally pure metals cooled to about 190 degrees, 

 Profs. Dewar and Fleming have established 

 that every pure metal would in all probability 

 have no electrical resistance at the zero of ab- 

 solute temperature, or, in other words, would 

 become a perfect conductor of electricity. In 

 this condition the passage of an electric current 

 would generate no heat in it. Another conse- 

 quence would be that a pure metal at the abso- 

 lute zero would form an absolutely opaque screen 

 to electro-magnetic radiation. These experi- 

 ments furnished an additional proof that the pro- 

 cess, by which an electric current was conveyed 

 from place to place was primarily dependent on 

 actions going on outside that which we usually 

 spoke of as a conductor. At the absolute zero 

 any electric power, however large, could be 

 transmitted along metallic wires, however 

 small, without loss of energy, the wire becom- 

 ing then a mere boundary and the energy-con. 

 veying processes being all effected in the non- 

 conductor outside of it. Diagrams were shown 

 illustrating the great increase in the conductiv- 

 ity of mercui-y on freezing. At its freezing 

 point its conductivity rose fourfold, and beyond 

 that point increased in such a way as to show 

 that at the absolute zero its conductivity would 

 be perfect. The peculiar differences in the re- 

 sistance of pure and slightly impure bismuth 

 were described, and proof was adduced that the 

 result of taking the electric resistance of a wire 

 of any metal in liquid air afforded a conclusive 

 test of its chemical purity. It was found that 

 the remarkable property possessed by bismuth 

 of undergoing a great increase in electrical resist- 

 ance when placed in a magnetic field was in- 



creased several hundred per cent, by the cold of 

 liquid air. In contrast with metals, carbon and 

 non-metallic bodies increased in electric resist- 

 ance as their temperature was reduced, this in- 

 crease continuing to take place as far as the low- 

 est temperature reached. In conclusion. Prof. 

 Fleming laid stress on the value of the knowl- 

 edge gained about the electrical resistance of 

 metals at low temperatures as a means of test- 

 ing the purity of a metal almost rivalling the 

 spectroscope in delicacy, and said that the facts 

 collected would prove of importance in judging 

 the validity of existing hypotheses of electric 

 and magnetic action, while at the same time 

 they opened out a wide field for fascinating 

 research in a region hitherto but little explored. 



THE DIMINUTION OF CONSUMPTION. 



Dr. Arthur Ransome contributes to the 

 Lancet (July 11) an article on ' Tuberculosis 

 and Leprosy,' in which he draws a parellel be- 

 tween the two diseases, (1) in their specific 

 causation and in their morphology; (2) in their 

 pathology; (3) in their distribution; (4) in their 

 general history and the conditions favorable or 

 otherwise to their existence; and (5) in their in- 

 fectiveness and hereditary transmission. 



There are many points of similarity between 

 them, and the author states that many authori- 

 ties are inclined to believe from a study of their 

 morphology that they are identical in character 

 and that their bacilli are modifications of one 

 species altered only by their environment. Dr. 

 Ransome does not, however, regard the dis- 

 eases as absolutely identical, but believes that 

 they are at least so far alike as to make it per- 

 missible from a study of the decline of one com- 

 plaint and its causes to attempt to glean some 

 idea of the most hopeful means of diminishing 

 the other; and that it is possible to go further and 

 prophesy that as one disease, leprosy, has dis- 

 appeared from our midst, so the other, tubercle, 

 may also be made to vanish, and that from the 

 recognition of its predisposing causes we may 

 learn in what way it may best be attacked and 

 finally driven from amongst civilized nations. 



Leprosy was banished mainly through gen- 

 eral sanitary measures and was scarcely affected 

 by direct efforts at preventing conta:gion. The 

 author considers it, therefore, only necessary 



