Karl T. Compton

Abridgment of the electric arc

DEFINITION OF ARC. An arc is a discharge of electricity, between electrodes in a gas or vapor, which has a voltage drop at the cathode of the order of the minimum ionizing or minimum exciting potential of the gas or vapor. ARC CHARACTERISTICS. The relation of arcs to glow discharges and coronas is illustrated by discussion of “generalized” curve of the gas discharge characteristic. Empirical equations for arc characteristics are interpreted, and a dependence on the boiling temperature of the anode is shown. Seeligers experiments on the transition from glow to arc, accompanied by the development of a cathode spot, show that the mechanism of the current at the cathode is fundamentally different in the two types of discharge. CATHODE SPOT. An analysis based on heat conduction in the cathode shows that the cathode spot has no sharp thermal definition, but does have a sharp boundary if defined by visual brightness or by thermionic emission. The phenomenon of moving cathode spots presents the problem of accounting for the observed temperatures. THEORIES OF CATHODE FALL. Comptons theory is based on space charge considerations and the assumption that the thickness of the fall space is equal to the electronic mean free path. Langmuirs theory differs from Comptons in assuming this thickness to be considerably less than a free path. Considerations of energy balance at the cathode definitely support Langmuirs rather than Comptons theory. ENERGY BALANCE AT CATHODE. Calorimetric measurements permit an estimate of the fraction of the current at the cathode which is carried by electrons. Though uncertain, the data are accurate enough definitely to support Langmuirs theory and to indicate that, in many cases, thermionic emission of electrons from the cathode is supplemented by a “pulling out” of electrons by the electric field which is concentrated at the cathode surface. Factors which determine the anode drop and the potential fall and ionization in the negative glow and the positive column are briefly discussed.

Technical progress and social development

Technology has made enormous contributions to modern society, but there still remain many attention-challenging aspects of its influence upon social development; some of these aspects are discussed here by this noted scientisteducator, who says that many future social developments can be realized only through better technical developments and better management. The type of management that is most likely to be successful in the long run will direct and inspire, but not too rigidly control.

The Electron: Its Intellectual And Social Significance

WITHIN the past five years, centenaries, bicentenaries and tercentenaries have been much in vogue. Every town or institution or event which has claim to distinction has sought the excuse of the calendar to remind the world of its claims to greatness. Thus we have recently celebrated the centenary of Faradays discovery of the principles of electromagnetism and the bicentenary of Watts invention of the steam engine discoveries which have introduced the eras of electricity and of mechanical power. The city of Chicago has sought to tell us that the progress of mankind really began with the founding of that community, and has led us to spend millions of dollars to gain the impression that there is really some causal relationship between Chicago and world progress. In my part of the country, the city of Boston and its suburbs staged a succession of tercentenary celebrations, as proud of their past as Chicago is of its present. Greatest of all was last summers tercentenary celebration of Harvard University, signalizing the firm basis of intellectual freedom and leadership which is the prime requisite for a free people in a democracy.

Chemical and Spectroscopic Properties of Excited Atoms and Reversible Effects of Electron Impacts in Gases

Excited Atoms. Attention is called to the accumulating evidence that normal atoms and those which are “excited” by the displacement of an electron to an outer orbit may have very different physical, chemical, and spectroscopic properties. Thus all atoms, even the inert atoms like helium, are electronegative when excited and tend to form homopolar and heteropolar compounds and negative ions. These compounds and ions are often sufficiently stable to exist for some time in a discharge tube. In any case they profoundly affect the spectrum of the substance.Reversible Effects of Impacts. Klein and Rosseland point out reasons for believing that an excited atom may revert to the normal state by transferring its energy to a free electron at a collision as well as by radiation. Franck points out that such radiationless transfers of energy may also occur at a collision between an excited and a normal atom.Phenomena due to Radiationless Transfers of Energy. Franck and Cario show that such transfers of energy may account for (1) the quenching of fluorescence by foreign gases, (2) the excitation of the spectrum of one metal vapor by resonance radiation of another vapor which is mixed with it, (3) the dissociation of hydrogen by mercury 2536 A radiation when mercury vapor is mixed with the hydrogen. These suggestions are critically reviewed.

Engineers and national security

NO ONE COULD help but be deeply appreciative of the honor of being selected as a recipient of the Hoover Medal. Few, if any, of the recipients will have had such reason as I for a feeling of humility when we compare our attempts to serve our community and nation with the high standards set by the donor of this medal, Conrad N. Lauer, and by the great American, Herbert Hoover, in whose honor the medal was named and who was its first recipient.

ORGANIZATION OF AMERICAN SCIENTISTS FOR THE WAR

IN America we have two principal scientific societies which are broadly representative of all the fields of science and which are rather parallel to the Royal Society of London and the British Association for the Advancement of Science. Dr. Frank B. Jewett, president of the National Academy of Sciences, has asked me to deliver his personal message to the president of the Royal Society of London, Sir Henry Dale, and in addition he requested me to express the admiration which is felt by the members of the National Academy of Sciences for the magnificent manner in which the scientific men of Great Britain have thrown the whole weight of their energies and abilities to master the innumerable technical problems arising in this War. He wanted me to assure you that in so far as we can do likewise, we in America are making a sincere effort to handle our similar problems and co-operatively to supplement the great work which you are doing.

Gerard Swope — Hoover medalist

GERARD Swope is presented for the Hoover Medal on the ground of his “constructive public service in the field of social, civic, and humanitarian effort.” One of his humanitarian efforts has been to help me on many occasions in the consideration of measures for improving the educational work of the Massachusetts Institute of Technology, of which he is an executive committee member.

Frank Baldwin Jewett — John Fritz medalist

The qualifications of the 1939 recipient of the highest American engineering honor are those of a leader, a statesman, and a nobleman of science.

What's Next in Science?

IT IS AN ALL TOO COMMON practice of scientific publicists and prognosticators to give free vent to their imaginations in a most unscientific way by picturing our descendants as flying through interplanetary space, after the manner of Buck Rogers or operating a navy with a thimbleful of transmuting atoms or banishing old age by administration of glandular extracts. No doubt many of the past triumphs of science were, relatively to the times, as spectacular and even more unexpected than these would be. However, scientific progress is not a great leap of imagination, but a steady process, like the advance of a great army; at times strategic positions are captured, as when the positive electron (positron) was discovered;at times there is a steady “mopping up” process all along the line, as when the systematic search for chemical isotopes followed the first discovery; at times there is retreat, as when a theory is proved untenable; at times a new powerful engine of this scientific war is invented, like the radio tube amplifier. While the scientific campaign is generally well planned in advance and directed toward certain main objectives, it also, on occasion, is opportunistic in that its center of activity may quickly be shifted by some new discovery or idea which discloses new territories to be conquered.

What's Next In Science?

* President, Massachusetts Institute of Technology. Address delivered before the American Association for the Advancement of Science, St. Louis, Mo., Dec. 30, 1935. IT is an all too common practice of scientific publicists and prognostieators to give free vent to their imaginations in a most unscientific way by pieturing our descendants as flying through interplanetary space, after the manner of Buck Rogers-or operating a navy with a thimbleful of transmuting atoms-or banishiug old age by administration of glandular extracts. No doubt many of the past triumphs of science were, relatively to the times, as spectacular and even more unexpected than these would be. Howevcr, scientific progress is not a great leap of imagination, but a steady process, like the advance of a great army; at times strategic, positions are captured, as when the positive electron (positron) was diecovered; at times there is a steady &dquo;mophing up&dquo; process all along the line, as when the systematic search for chemical isotopes followed the first discovery; at times there is a retreat, as when a theory is proved untenable; at times a new powerful engine of this scientific war is invented, like the radio tube amplifier. While the scientific campaign is generally well planned in advance and directed toward certain main objectives, it is also, on occasion, opportunistic in that its center of activity may be quickly shifted by some new discovery or idea which discloses new territories to be conquered. A better analogy to scientific progress is geogralhical exploration. Just as the discovery of the Great Lakes and the Ohio, Mississippi and Missouri Rivers led to their use as avenues of colonization, so great scientific discoveries and theories are the channels for widespread advance of Scientific knowledge. Similarly there are desert and mountain barriers in