Septembee 14, 1906.] 



SCIENCE. 



347 



one sixth of the present market price, and 

 give promise of an ultimate low price of a 

 fraction over two cents per gallon. The re- 

 sult is secured by purely mechanical means, 

 without an atom of added chemicals. At- 

 mospheric air is first purified and then com- 

 pressed by stages to 2,500 pounds to the square 

 inch. It is finally reduced to 125 pounds to 

 the square inch, which then cools and liquefies 

 the high-pressure air. The oxygen gas pro- 

 duced by separating the nitrogen from the 

 liquid air is claimed to be purer than that of 

 the old method, and can be supplied in the 

 liquid as well as in the gaseous form. One 

 gallon of liquid air equals approximately 128 

 cubic feet of oxygen gas, which retails at six 

 cents per cubic foot. The new price is one 

 cent. Liquid air has been successfully used 

 in coal as an explosive, being quite safe where 

 fire damp and other explosive gases exist. 

 Liquid oxygen is also used for welding steel 

 pipes, boiler shells and plates for shipbuilding 

 instead of riveting. That oxygen and nitro- 

 gen can be separated from liquid air and sold 

 retail at $1.20 per gallon shows great com- 

 mercial possibilities. The use of nitrogen for 

 agricultural purposes opens yet another field. 

 The maturing of liquors will be helped by 

 liquid air, as also the preservation and purifi- 

 cation of milk. As a motive power its use is 

 considered to be quite practicable for small 

 powers. The British government is already 

 carrying out a number of experiments with a 

 view to the utilization of liquid air for various 

 purposes. 



RADIUM} 



I venture to think that the thanks of the public 

 are due to Lord Kelvin for his timely and out- 

 spoken protest against the conclusion being drawn, 

 from the evidence at present before us, that it is 

 proved that there is a 'gradual evolution of one 

 element into others.' No one has yet handled 

 ' radium ' in such quantity or in such manner 

 that we can say what it is precisely. That 



' Correspondence in the London Times, called 

 forth by a letter from Lord Kelvin, reprinted in 

 the issue of Science for August 24, p. 255. 



helium can be obtained from ' radium ' appears to 

 be proved; but no proof has yet been given that 

 it is not merely contained in it. As I remarked 

 at York last week, physicists are strangely inno- 

 cent workers; formulae and fashion appear to ex- 

 ercise an all-potent influence over them. There 

 was a time when the expression ' scientific cau- 

 tion ' meant the highest degree of caution, and 

 it was supposed to be the attribute of workers in 

 science. Workers in the radium school appear to 

 have cast caution to the winds and to have sub- 

 stituted pure imagination for it. Among our- 

 selves, we should always be at liberty to postulate 

 the most crack-brained of hypotheses, to dream 

 the wildest of dreams, as a means of guiding 

 inquiry; but we should not court popularity on 

 such a basis. By so doing we lose all claim to 

 guide public opinion. Henry Armstrong. 



I am glad to have contributed towards eliciting 

 Lord Kelvin's views on this subject. Those in- 

 terested will no doubt judge for themselves 

 whether or not the precautions adopted by 

 Ramsay and Soddy, Himstedt and Meyer, and 

 Curie were such as to make it certain that helium 

 is continuously evolved from radium, as those 

 writers supposed. 



As to the internal heat of the earth, Lord Kelvin 

 quotes the generally accepted conclusion that the 

 life of radium is limited to a few thousand years. 

 From this he argues that the radium now in ex- 

 istence has not been there long enough to heat 

 the earth to its present high internal tempera- 

 ture. To this I reply that it is true that the 

 actual radium now in existence has not done the 

 work throughout, but that the supply of radium 

 in the earth is maintained at a constant level by 

 the production of fresh radium by uranium, con- 

 tained in a small proportion in the rocks. Lord 

 Kelvin, anticipating this reply, expresses his dis- 

 sent from the view, current among workers on 

 radioactivity, that radium is continuously pro- 

 duced by uranium. I should like to ask a simple 

 question. Lord Kelvin disbelieves that radium 

 is being generated from any parent substance. 

 How does he explain the existence of radium in 

 the earth at present? On his own showing the 

 identical radium now existing has not been there 

 long. Is he prepared to assume that it was 

 miraculously created in comparatively recent 

 times? E,. J. Strutt. 



In your yesterday's issue I see letters of Sir 

 Oliver Lodge and Mr. R. J. Strutt, replying to 



