LOW-TEMPERATURE RESEARCHES 



about liquid water, or liquid mercury, or liquid iron. 

 Long before air was actually liquefied, it was perfectly 

 understood by men of science that under certain con- 

 ditions it could be liquefied just as surely as water, mer- 

 cury, iron, and every other substance could be brought 

 to a similar state. This being known, and the princi- 

 ples involved understood, had there been nothing 

 more involved than the bare effort to realize these con- 

 ditions all the recent low - temperature work would 

 have been mere scientific child's-play, and liquid air 

 would be but a toy of science. But in point of fact 

 there are many other things than this involved ; new 

 principles were being searched for and found in the 

 course of the application of the old ones ; new light was 

 being thrown into many dark corners; new fields of 

 research, some of them as yet barely entered, were be- 

 ing thrown open to the investigator; new applications 

 of energy, of vast importance not merely in pure 

 science but in commercial life as well, were being made 

 available. That is why the low-temperature work 

 must be regarded as one of the most important scien- 

 tific accomplishments of our century. 



At the very outset it was this work in large measure 

 which gave the final answer to the long-mooted ques- 

 tion as to the nature of heat, demonstrating the cor- 

 rectness of Count Rumford's view that heat is only 

 a condition not itself a substance. Since about the 

 middle of the century this view, known as the mechan- 

 ical theory of heat, has been the constant guide of the 

 physicists in all their experiments, and any one who 

 would understand the low-temperature phenomena 

 must keep this conception of the nature of heat clearly 



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