« PreviousContinue »
travelling with its plane perpendicular to the direction of motion.
It is clear from the experiments with hydrogen that, for distances of the order of the diameter of the electron, the a-particle no longer behaves like a point charge, but that the a-particles must have dimensions of the order of that of the electron. The closest distance of approach in these collisions in hydrogen is about one tenth the corresponding distances in the case of a collision of an a-particle with an atom of gold.
The results obtained with hydrogen in no way invalidate the nucleus theory as used to explain the scattering of a-rays by heavy atoms, but show, as we should expect, that the theory breaks down when we approach very close to the nucleus structure. In our ignorance of the constitution of the nucleus of the a-particle, we can only speculate as to its structure and the distribution of forces very close to it. If we take the a-particles of mass 4 to consist of four positively charged H nuclei and two negative electrons, we should expect it to have dimensions of the order of the diameter of the electron, supposing, as seems probable, that the H nucleus is of much smaller dimensions than the electron itself. When we consider the enormous magnitude of the forces between the a-particle and the H nucleus in a close collisionamounting to 6 kg. of weight-it is to be expected that the structure of the a-particle should be much deformed, and that the law of force may undergo very marked changes in direction and magnitude for small changes in the closeness of approach of the two colliding nuclei. Such considerations offer a reasonable explanation of the anomalies shown in the number and distribution with velocity of the H atoms exhibited for different velocities of the a-particles.
When we consider the enormous forces between the nuclei, it is not so much a matter of surprise that the nuclei should be deformed as that the structure of the a-particle or helium nucleus escapes disruption into its constituent parts. Such an effect has been carefully looked for, but so far no definite evidence of such a disintegration has been
observed. If this be the case, the helium nucleus must be a very stable structure to stand the strain of the gigantic forces involved in a close collision.
We have seen that the recoil atoms of all elements of atomic mass less than 18 should travel beyond the range of the a-particle, provided they carry a single charge. Preliminary experiments, in which the a-particles passed through pure helium, showed that no longrange recoil atoms were present, indicating that after recoil the helium atom carries a double charge. In a similar way no certain evidence has been obtained of long-range recoil atoms from lithium, boron, or beryllium. It is difficult in experiments with solids or solid compounds to be sure of the absence of hydrogen or water-vapor, which results in the production of numerous swift H atoms. These difficulties are not present in the case of nitrogen and oxygen, and a special examination has been made of recoil atoms in these gases. Bright scintillations were observed in both these gases about 2 cm. beyond the range of the a-particle. These scintillations are, presumably, due to swift N and O atoms carrying a single charge, for the ranges observed are about those to be expected for such atoms. The scintillations due to recoil atoms of N and O are much brighter than H scintillations, although the actual energy of the flying atom is greater in the later case. This difference in brightness is probably connected with the much weaker ionization per unit of path due to the swifter H atom.
The corresponding range of the recoil atoms was about the same in oxygen, nitrogen and carbon dioxide. Theoretically, it is to be anticipated that the N recoil atom should give a somewhat greater range than the O atom. The recoil atoms observed in carbon dioxide are apparently due to oxygen, for if the carbon atoms carried a single charge they should be detected beyond the range of O
The number of recoil atoms in nitrogen and oxygen and their absorption indicate that these atoms, like H atoms, are shot forward mainly in the direction of the a-particles. It
is clear from the results that the nuclei of the atoms under consideration can not be regarded as point charges for distances of the order of the diameter of the electron. Taking into account the close similarity of the effects produced in hydrogen and oxygen, and the greater repulsive forces between the nuclei in the later case, it seems probable that the abnormal forces in the case of oxygen manifest themselves at about twice the distance observed in the case of hydrogen, i. e., for distances less than 7 X 10-18 cm. Such a conclusion is to be anticipated on general grounds, for presumably the oxygen nucleus is more complex and has larger dimensions than that of helium.
In his preliminary experiments Marsden observed that the active source always gives rise to a number of scintillations on a zinc sulphide screen far beyond the range of the a-particle. I have always found these natural scintillations present at the sources of radiation employed. The swift atoms producing these scintillations are deflected in a magnetic field, and have about the same range and energy as the swift H atoms produced by the passage of a-particles through hydrogen. The number of these natural scintillations is usually small, and it is very difficult to decide definitely whether such atoms arise from the disintegration of the active matter or are due to the action of the a-particles on hydrogen occluded in the source.
These natural scintillations were studied by placing the source in a closed box exhausted of air about 3 cm. from an opening in the end covered by a sheet of silver of sufficient thickness to stop the a-rays completely. The zinc sulphide screen was fixed outside close to the silver plate. On introducing dried oxygen or carbon dioxide into the vessel, the number of scintillations fell off in amount corresponding with the stopping power of the column of gas. An unexpected effect was, however, noticed on introducing dried air from the room. Instead of diminishing, the number of scintillations was increased, and for an absorption equivalent to 19 cm. of air the number was about twice that observed when the air was exhausted. It was clear
from the results that the a-particles in their passage through air gave rise to long-range scintillations which appeared of about the same brightness as H scintillations. This effect in air was traced to the presence of nitrogen, for it was shown in dry, chemically prepared nitrogen as well as in air. The number of scintillations was much too large to be accounted for by the presence of traces of hydrogen or water-vapor, for the effect observed was equivalent to the number of H atoms produced by the mixture of hydrogen at 6 cm. pressure with oxygen. The measurements were always made well outside the range of the recoil nitrogen and oxygen atoms, which we have seen are stopped by 9 cm. of air.
These swift atoms which arise from nitrogen have about the same brightness and range as the H atoms produced from hydrogen, and, presumably, are charged hydrogen atoms. Definite information on this point should be obtained by measuring the deflection of a pencil of these atoms in a magnetic and electric field. The experiments are, however, exceedingly difficult on account of the very small number of the scintillations to be expected under the experimental conditions. It should be mentioned that the evidence so far obtained is not sufficient to distinguish definitely whether these are H atoms or atoms of mass 2, 3, or 4, for the range and brightness of the latter would not be very different from those shown by the H atom.
It is difficult to avoid the conclusion that these long-range atoms arising from the collision of a-particles with nitrogen are not nitrogen atoms, but probably charged atoms of hydrogen or atoms of mass 2. If this be the case, we must conclude that the nitrogen atom is disintegrated under the intense forces developed in a close collision with swift a-particles, and that the atom liberated formed a constituent part of the nitrogen nucleus. It may be significant that from radio-active data we should expect the nitrogen nucleus of atomic mass 14 to consist of three helium nuclei of mass 4, and either two hydrogen nuclei or one nucleus of mass 2.
The effect produced in nitrogen would be
accounted for if the H nuclei were outriders of the main nucleus of mass 12. The close approach of the a-particle leads to the disruption of its bond with the central nucleus, and under favorable conditions the H atom would acquire a high velocity and be shot forward like a free hydrogen atom. Taking into account the great energy of the particle, the close collision of an a-particle with a light atom seems to be the most likely agency to promote its disruption. Considering the enormous intensity of the forces brought into play in such collisions, it is not so much a matter of remark that the nitrogen atom should suffer disintegration as that the a-particle itself escapes disruption. The results, as a whole, suggest that if a-particles or similar projectiles of still greater energy were available for experiment, we might expect to break down the nucleus structure of many of the lighter atoms.
SECOND AWARD OF THE ELLIOT
THE Elliot Medal is awarded annually by the National Academy of Sciences to the author of the leading publication of the year in zoology or paleontology. The first award Iwas made for the year 1917 to Frank M. Chapman for his volume "The Distribution of Bird-Life in Columbia," published by The American Museum of Natural History. The second award for the year 1918 was to William Beebe, of the New York Zoological Society, on the completion of the first volume of his work on the "Pheasants."
In presenting Mr. Beebe to the Academy for the award, Professor Henry Fairfield Osborn made the following remarks:
Daniel Giraud Elliot, to whom the Academy is indebted for the Elliot Medal, was a leading ornithologist and mammalogist of the old school. He produced a series of splendid monographs on birds and mammals, and closed his scientific career with an exhaustive revision of the Primates. With the exception of a journey in Africa the greater part of his life was spent in museums, yet I believe if he
were living he would not hesitate a moment to award the Elliot Medal for the Year 1918 to William Beebe on the completion of the first volume of his great work "A Monograph of the Pheasants."
This is a profound study of the living pheasants in their natural environment in various parts of eastern Asia. There are nineteen groups of these birds; eighteen were successfully hunted with the camera, with field-glasses, and when necessary for identification, with the shotgun. The journey occupied seventeen months, extended over twenty countries, and resulted in a rare abundance of material, both literary-concerning the life histories of birds-and pictorial, photographs and sketches. The journey extended over 52,000 miles; it ended in the great Museums of London, of Tring, of Paris, and of Berlin, for the purpose of studying the type collections. Thus the order of the work was from nature to the museum and to man, rather than from man and the museum to nature. It is this distinguished note of direct observation of natural processes, under natural conditions, which is needed to-day in biology to supplement the note of the laboratory and of experiment. Living birds and living mammals have as much to teach us in their natural surroundings as they taught Darwin and Wallace and we must endeavor to keep the eyes and minds of these great naturalists in our modes of vision.
The monograph covers the blood partridges, the tragopans, the impeyans, the gold and silver pheasants, the peacocks, the jungle fowl, and the history of the ancestry of our domestic fowls. It has important bearings on the Darwinian theories of protective coloration and of sexual selection, and on the De Vries theory of mutation. The full-grown male and female characters, the changes of plumage from chick to adult, the songs, courtships, battles, nests and eggs of nearly one hundred species are included and systematically described. The illustrations are by leading American and British artists. The haunts of the pheasants are shown in the author's photographs ranging from the slopes of the Himalayan snow-peaks, 16,000 feet
above the sea, to the tropical seashores of Java. Like Chapman's "Birds of Columbia," to which the Elliot Medal was awarded last year, this monograph puts the living bird, in its living environment, into the forefront.
It is for these reasons that the committee was unanimous, especially when its decision was confirmed without hesitation by Dr. J. A. Allen, the Nestor of American zoologists. It is not the magnificence of this monograph, not the superb illustrations, not the delightfully written text, but the truly Darwinian spirit which animated the author and which sustained him through seven years of continuous research and his arduous labors in the preparation of this monograph. When completed, we believe that it will come nearer to depicting the actually living forms of this great group than any book which has ever been written on a single family of birds.
PROPOSED CONSTITUTION AND BYLAWS OF THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE
THIS Copy of the Constitution and By-laws is the one presented to the Committee on Policy by the subcommittee on revision. It was adopted by the committee and presented to the association at the Baltimore meeting. It will be presented for adoption at the St. Louis meeting.
EDWARD L. NICHOLS, Chairman of the Committee on Policy
CONSTITUTION OF THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE
Article 1. Objects
The objects of the Association are to promote intercourse among those who are cultivating science in different parts of America, to cooperate with other scientific societies and institutions, to give a stronger and more general impulse and more systematic direction to scientific research, and to procure for the labors of scientific men increased facilities and a wider usefulness.
Article 2. Membership
Persons willing to cooperate in the work of the Association may be elected to be members by the
Council. Members who are professionally engaged in scientific work or who have advanced science by research may be elected to be Fellows. The admission fee for members is five dollars; the annual dues are four dollars.1 A member who pays at one time the sum of seventy-five dollars to the Association becomes a life member and is exempt from further dues. A person who gives one thousand dollars to the Association may be elected to be a sustaining member and is exempt from further dues.
Article 3. Officers
The officers of the Association shall be elected by ballot by the Council, and shall consist of a President, a Vice-president from each section, a Permanent Secretary, a General Secretary, a Treasurer and a Secretary of each section. The President and the Vice-presidents shall be elected for one year, the other officers for four years. The officers shall perform the usual duties of these offices under the direction of the Council.
Article 4. Council
The Council shall consist of the President, the Vice-presidents, the Permanent Secretary, the General Secretary, the Secretaries of the Sections, and the Treasurer, of one fellow elected by each affiliated society and one additional fellow from each affiliated society having more than one hundred members who are fellows of the Association, and of eight fellows, two elected annually by the Council for a term of four years. There shall be an Executive Committee of the Council, consisting of the President, the Permanent Secretary, the General Secretary, and eight members elected by the Council, two annually for a term of four years. The Council may appoint standing or temporary committees to make reports, to assist in the conduct of the work of the Association and to promote its objects.
Article 5. Sections
The Association shall be divided into the following Sections: A, Mathematics; B, Physics; C, Chemistry; D, Astronomy; E, Geology and Geography; F, Zoological Sciences; G, Botanical Sciences; H, Anthropology and Archeology; I, Psychology and Philosophy; J, Social and Economic Sciences; K, Historical and Philological Sciences; L, Engineering; M, Medicine; N, Agriculture; 0,
1 The Committee on Policy recommends that the annual dues be five dollars and the life membership fee one hundred dollars.
Manufactures and Commerce; P, Education. Members of the Association shall be members of that Section or of those Sections under which their work or their interests fall. Members of the Section shall nominate to the Council a Chairman, who becomes ex officio a Vice-president of the Association and whose term of office shall be one year, and a Secretary, whose term of office shall be four years. These officers, together with four fellows, one elected annually by the Section for a term of four, years, and the representatives on the Council of affiliated societies in the same field shall form a Sectional Committee. This committee shall arrange the scientific programs of the meetings and may form sub-sections or hold joint meetings with other sections or other societies. It may appoint committees and shall in all ways promote the objects of the Association within its own field.
Article 6. Divisions and Branches Regional Divisions and Local Branches of the Association may be formed by vote of the Council. Such Divisions and Branches may elect officers, hold meetings, appoint committees, enter into relations with other societies and promote within their fields the objects of the Association.
quests and gifts will be administered in accordance with the provisions of the donors. The payments from sustaining and life members form part of the permanent fund, and the income (after the death of the member) shall be used for research, unless otherwise directed by unanimous vote of the Council or by a majority vote at two consecutive annual meetings.
Article 11. Alteration of the Constitution This Constitution may be amended at a General Session by unanimous vote or by a majority vote at two consecutive annual meetings.
BY-LAWS AND RULES OF PROCEDURE
The Association is American, its field covering North, Central and South America. Inhabitants of any country are eligible to membership.
1. An incorporated scientific society or institution or a public or incorporated library may become a member by vote of the Council.
2. Associates on payment of four dollars may be admitted to the privileges of a meeting, except voting.
3. Foreign associates may be admitted without fee to the privileges of a meeting, except voting. 4. All members who are professionally engaged in scientific work, or who have advanced science by research, may be elected by the Council to be fellows on nomination or on their own application. This qualification is understood to have been met by members of affiliated societies having a research qualification.
5. The Council may exclude from the Association any one who has made improper use of his membership or whose membership is regarded as detrimental to the Association.
1. The Permanent Secretary, the General Secretary and Treasurer of the Association and the Secretaries of the Sections shall be elected at the larger convocation week meetings held once in four years beginning the last week of the year 1916. Vacancies in these offices shall be filled by the Council.
2. The President of the Association shall give an address at a general session of the Association at the annual meeting following that over which he presided.