704 Miss Agnes M. ClerJce 



hindered, but the approach of an universally diffused element. 

 Facts learned by its use are indeed to be reckoned among the spolia 

 opima of nature ; they represent the trophies of an arduous conflict. 



Effects of Refrigeration. 



Research into the effects of refrigeration is almost co-extensive 

 with the whole realm of physics. It is concerned with the relations 

 of matter to light, heat, electricity and magnetism. Questions as to 

 the mode of action of cohesive and chemical forces come fully within 

 its scope; nor is it possible to exclude from it the consideration of 

 the intricacies of molecular structure, or even of the essential nature 

 of material substance. These ultimate problems force themselves 

 upon the attention of the least speculative " cryogenist." The nearer 

 absolute zero can be approached, the more hopeful becomes the pro- 

 spect of their definitive solution ; and towards this " pole of cold " 

 Professor Dewar has been pressing his way during two decades. Its 

 actual attainment may perhaps be impossible ; but the separating 

 interval must be reduced to a minimum. The ground already won 

 has meanwhile been carefully surveyed. Contemporaneously with 

 unceasing efforts for the liquefaction of hydrogen, experiments were 

 vigorously prosecuted at the temperature of liquid air. Resuming 

 the subject of electrical resistance, Professors l)ewar and Fleming 

 carried out in 1893, and several subsequent years, an extensive series 

 of inquiries, with more complete appliances than before for the pro- 

 duction of refrigerating material in large quantities, with greater 

 care in the preparation of the metallic wires submitted to trial, and 

 with more delicate precautions in the physical measurements executed. 

 The earlier result was confirmed that the resistivity of all pure 

 metals falls off with increase of cold, but many abnormalities and 

 peculiarities were brought to light. The various metals do not, in 

 all cases, maintain the same relative places on the scale. At — 200° 0. 

 copper is a better conductor than silver, iron than zinc, aluminium 

 than gold. The electrical eccentricities of bismuth cost the investiga- 

 tors protracted toil. They finally disclosed their origin from minute 

 chemical impurities, by disappearing when electrolytic bismuth was 

 employed. The further discovery was made that the known effect of 

 a magnetic field in augmenting the resisting power of a bismuth wire 

 is greatly intensified at the temperature of liquid air. That of so- 

 called insulators, such as glass, ebonite, guttapercha, and paraffin, 

 likewise gains as heat is subtracted. Alloys follow the opposite rule 

 — that obeyed by pm*e metals — but in a half-hearted way, and with 

 many perplexing incongruities. When liquid hydrogen was made 

 amenable to control, it became possible to push these inquiries con- 

 siderably further. At this lower depth of cold, the resistance of 

 copper diminished to T J 3 th its efficacy at the temperature of melting 

 ice, that of gold to ^th, while |4h the initial resistance of iron sur- 

 vived. The general upshot was besides most significant. It had been 



