Page:Popular Science Monthly Volume 65.djvu/571

Rh and an address by Professor J. H. Poynting on 'Radiation in the solar system.' A number of papers were presented to the section by foreign visitors including two by Professor Wood, of the Johns Hopkins University, one describing some recent improvements in the diffraction process of color photography and another on the anomalous dispersion of sodium vapor. Section A includes mathematics and astronomy as well as physics. Among the papers was one by Sir David Gill, director of the observatory at the Cape of Good Hope, entitled 'Problems of Astronomy.' which discussed some of the questions in practical astronomy now pressing for solution.

Before the Chemical Section Sir James Dewar gave an address on very low temperature phenomena with interesting demonstrations. He showed by a series of beautiful vacuum-tube experiments the behavior of nitrogen, oxygen, hydrogen and argon when submitted in contact with charcoal to the cooling influence of liquid air. The nitrogen tube exhibited the usual violet color when the spark passed through it, but as soon as the charcoal was immersed in the liquid air the tube passed through various stages of attenuated brilliancy until ultimately the vacuum became so high that the current could scarcely overcome the resistance. When the liquid air was removed the changes were passed through in the reverse order. Oxygen passed through a similar series of changes, but in the case of hydrogen the absorptive power of the charcoal at the temperature of liquid air was not great enough to render the tube non-conductive. Lord Kelvin, in proposing a vote of thanks to Professor Dewar, said that he was filled with expectation as to the condition of things that would be disclosed at a temperature of 5° absolute, where there would be 110 motion. What would become of electric conductivity, of magnetism, of thermal conductivity? He wished Sir James would continue his electroconduct ivity experiments and bring him copper highly conductive at 8° but as great an insulator as glass at one or two or three degrees. Sir William Ramsay, speaking on the changes produced by the β-rays, said that he had obtained 105 milligrams of radium bromide, which, being too precious to risk in one vessel, were divided amongst three bulbs. These bulbs were placed in glass vessels, and were each provided with a tube to take away emanations. The vessels were colorless to start with, and were some of potash and some of soda glass, but in course of time the former became brown and the latter violet in color. The glass, too, became radio-active, but this property was removed by washing with water, although the color remained. When a solution of radium bromide was evaporated an invisible residue was left which was radio-active and dissolved to a radio-active solution. Radium formed chloride, sulphide, hydroxide and sulphate similar to lead, except that they were radio-active. The radium emanations rendered silver and platinum as well as glass radioactive. Professor W. O. Atwater, of Wesleyan University, presented two papers, one on the agricultural experimental work in the Smithsonian Institution and one on the experiments in nutrition carried out under his direction.

Mr. Aubrey Strahan's presidential address before the geological section was on earth movements, and this was taken as a subject for special discussion. In opening it Mr. Straham said that the subject proposed for discussion was the nature and origin of those movements of the earth's crust which have manifested themselves in the factoring, overthrusting and folding of strata. These movements have been in operation from the earliest to the latest geological periods; and, though they have been intermittent so far as anyone region is concerned, there is reason to believe that they have been more or