Lapas attēli
PDF
ePub
[merged small][ocr errors][merged small]

In Fig. 8 is shown a gyroscope whose wheel, pivoted in a frame, can be rotated rapidly about its axis A. Except for the action of two springs, the frame and the axis A are free to move in altitude about a horizontal axis B, making an angle with the vertical C; and the axis B and the whole instrument can be rotated about the vertical axis C. If the wheel is spun about the axis A, and the instrument then rotated about the vertical C, the wheel tips up or down so as to make the direction of its rotation coincide more nearly with the direction of the impressed rotation about the vertical axis C. If it were not for the springs, the wheel would tip until the axes A and C became coincident. The greater the rotary speed about the vertical the greater is the tip of the wheel. When the wheel's speed about the axis A is zero, no tip occurs.

Now if the magnetic molecule is a gyroscope, it will behave like this wheel. If the body of which it is a part is set into rotation about any axis, the molecule, or magneton, will change its orientation in such a way as to make its direction of rotation coincide more nearly with the direction of the impressed rotation; the coincidence will finally become exact if this is not prevented by the action of the rest of the body. This idea was in the

mind of Maxwell in 1861, and has occurred to a number of others since.

In an ordinary ferromagnetic. body in the usual state with which we are familiar only a slight change of orientation can occur on accunt of the forces due to adjacent molecules, which perform the function of the springs in the case of our gyroscope. The rotation causes each molecule to contribute a minute angular momentum, and thus also a minute magnetic moment, parallel to the axis of impressed rotation; and thus the body, whose magnetons originally pointed in all directions equally, becomes magnetized along the axis of impressed rotation. If the revolving electrons, or rotating magnetons, are all positive, the body will thus become magnetized in the direction in which it would be magnetized by an electric current flowing around it in the direction of the angular velocity imparted to it. If they are all negative, or if the action on the negative magnetons is preponderant, it will be magnetized in the opposite direction.

If R denotes the ratio of the angular momentum of a magneton, or an electron orbit, to its magnetic moment, it can readily be shown that rotating a magneton or electron orbit about any axis with an impressed velocity N revolutions per second, is equivalent to placing it in a magnetic field with intensity H directed along this axis such that

[blocks in formation]
[blocks in formation]

Now in two investigations on cold-rolled steel by a method of electromagnetic induction, a third investigation principally on steel, nickel and cobalt by a magnetometer method, and a fourth investigation on steel, soft iron, cobalt, and Heusler alloy by another magnetometer method, Mrs. Barnett and I have found the above theory verified, except that in place of the number 7.1 we find smaller numbers; in the best work, which appears to be free from any serious systematic error, we find instead of 7.1 numbers about one half as great and even smaller.21 This work, however, is still in progress.

If these results are correct, we seem to be driven to one of two conclusions: Either negative electrons or magnetons with a value of m/e or R for the motions involved different from that ordinarily accepted are responsible for magnetism; or positive electrons or magnetons, whose rotation we have seen must produce an opposite effect, are also involved. It does not seem impossible that a ring or other type of negative magneton, with R different for the permanent rotary motion from the value obtained from cathode ray experiments and otherwise, should be involved; but the presence of positive electron orbits, or rotating positive magnetons, is also possible, especially in view of the known expulsion of a particles with great velocities from the radioactive substances. Chemical evidence is often quoted in favor of the idea that superficial negative electrons alone are responsible for magnetism; but I do not think this evidence conclusive.

[ocr errors]

Not long after our first conclusive experiments on magnetization by rotation were communicated to this society, experiments on the converse effect, viz., rotation by magnetization, first suggested by Richardson, were performed by Einstein and deHaas.22 Mag

21 Phys. Rev., 6, 1915, p. 239; 10, 1917, p. 7; Proc. American Phys. Soc. for December, 1920; Proc. Phil. Soc. of Washington for October 9, 1920. 22 Verh. d. D. Phys. Ges., 17, 1915, p. 152.

netizing a bar of iron, in turning the magnetons about until they all rotate in the same direction, produces angular momentum in this direction which must be compensated by an angular momentum within the molecules themselves, or in the bar, or in the magnetizing solenoid. If we assume that the reactions all take place upon the bar we can calculate 4(m/e) from the measurable angular momentum communicated to it when magnetized to a given intensity on the assumption that all the magnetons are alike. The result published by Einstein and deHaas agreed closely with the value to be expected on the hypothesis that only the common type of negative electron is involved; but the sign of the effect was not determined with certainty till much later, and errors in the value of the assumed intensity of magnetization and in the experiments themselves undoubtedly exist. The experiments have been repeated with great improvements by Emil Beck, 23 and experiments on the same subject but by a different method had already been made by J. Q. Stewart;24 both these investigations, on the basis of a single kind of electron and on the assumption made above with reference to the seat of the reaction to the electron momentum, give values of 4π(m/e) for iron and nickel similar to those which Mrs. Barnett and I have found by the method of magnetization by rotation, into the theory of which no assumptions appear to enter except such as can be justified completely.

If a magneton is sufficiently free it will, as stated above, when rotated about a given axis align itself with its axis completely parallel to the axis of impressed rotation. If in the unit volume there are N magnetons all alike, each with the moment of inertia C and initial angular velocity U about the magnetic axis, and if the effects of collisions and the demagnetizing field are negligible, the intensity of magnetization will be

[merged small][merged small][ocr errors][merged small][merged small][merged small][merged small]

1

tion, just as, in Voigt's equation, the first term is independent of H. The orientation is here produced by the rotation, but only the time. taken to reach a steady state is affected by its magnitude. The second term, here added to the first, corresponds to Voigt's diamagnetic term. Here we have, except for the small second term, saturation for even very small values of Ω.

If collisions are not absent, or if the magnetic fields of adjacent molecules and the demagnetizing field become appreciable, the intensity of magnetization will not reach saturation; but it will increase with , being greater for a given value of the greater the mean interval between collisions, the less their violence, and the weaker the field.

It was suggested by Schuster in 1912 and by Einstein and deHaas in 1915, and earlier by myself, that the behavior of a magnetic molecule as a gyroscope might account for cosmical magnetism, as the direction of the magnetization of the earth and sun bear to the direction of the rotation the relation required by the theory. If the theory is quantitively sufficient, the interior of the earth and sun, as pointed out years ago, must be in a very different state from that of bodies with which we are familiar. If m/e reaches enormous values for magnetons within the earth and sun, which is not probable, or if the magneton density is sufficiently high and the effects of collisions and the molecular and demagnetizing fields at the same time sufficiently small, it is possible that even the small angular velocities of the earth and sun may be sufficient to produce the observed magnetizations.25

S. J. BARNETT DEPARTMENT OF TERRESTRIAL MAGNETISM, CARNEGIE INSTITUTION

THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE SPRING MEETING OF THE EXECUTIVE COMMITTEE

THE executive committee of the council of the association held its regular spring meeting

25 See papers by Professor S. Chapman and by myself in Nature, Nov. 25, 1920, and March 3,

1921.

in the Cosmos Club, Washington, D. C., on the afternoon and evening of Sunday, April 24. The following paragraphs summarize items of business that were transacted. The personnel of the executive committee is as follows:

Simon Flexner (chairman), J. McK. Cattell, H. L. Fairchild, L. O. Howard, W. J. Humphreys, B. E. Livingston (permanent secretary of the association), D. T. MacDougal (general secretary of the association), E. H. Moore (president of the association), A. A. Noyes, Herbert Osborn, H. B. Ward. All of the members were present at this meeting, excepting Messrs. Flexner, Moore, and Noyes. The meeting was called at 4.00 P.M.

After the minutes of the last meeting of this committee (Chicago, Dec. 29, 1920) had been read and approved it was voted that the next meeting of the executive committee shall occur in New York City on the first Sunday after November 1 that shall be convenient to a majority of the members," the exact date to be arranged by the permanent secretary.

It was voted that the action thus far taken by the American Association committee on conservation, be approved and that that committee be authorized to proceed with its plans. (The committee on conservation consists of J. C. Merriam (chairman), H. S. Graves, Barrington Moore, V. E. Shelford and Isaiah Bowman. It held a meeting in New York City on April 9, jointly with corresponding committees of the National Academy of Sciences and the National Research Council, and it was recommended that these three committees form a continuing joint committee on national conservation, representing the three organizations just mentioned, and that this joint committee be authorized to set up an executive and secretarial agency for the active prosecution of its work.)

The executive committee ratified the action taken by the committee on honorary life memberships through the Jane M. Smith fund, in placing the names of the distinguished scientists, J. E. Clark and J. N. Stockwell, recently deceased, on the list of honorary life members of the Association. (Both were ac

tive members of the Association from 1875 until death.)

Dr. J. C. Fields, president of the Royal Canadian Institute, was elected chairman of the local committee of the American Association, for the forthcoming Toronto meeting.

Dr. Sam F. Trelease (assistant secretary of the association) was elected secretary of the council for the Toronto meeting.

It was voted that a special committee consisting of the president, the permanent secretary, and the general secretary should arrange, in cooperation with the local committee for the Toronto meeting, for the invitation of an eminent British man of science to attend the Toronto meeting, to give a general public lecture on the evening of Friday, December 30, and to present such scientific papers as he may be willing to give, before the section of the association or the affiliated societies to which his field of science may be related.

It was voted that the British Association for the Advancement of Science be invited to be officially represented at the Toronto meeting. A committee consisting of the president and the two secretaries was authorized to invite representation by other organizations at the Toronto meeting. Dr. J. McK. Cattell was elected to be an official delegate of the American Association to attend the forthcoming Edinborough meeting of the British Association. The committee mentioned was authorized to appoint other representatives.

It was voted that the permanent secretary and the general secretary be constituted a special committee to render a decision in the case of any fellowship nomination for which the section secretary may fail to make definite recommendation. (Nominations for fellowship in the Association may be made by any member in good standing, including the nominee himself, and they are immediately referred, by the permanent secretary, to the proper section secretary, who investigates each nomination and transmits it, with his recommendation to the permanent secretary for reference to the executive committee. The executive committee acts for the council in electing fellows at the spring and autumn meet

[ocr errors]

ings of the committee and it recommends fellowship elections to the council when a council session follows promptly upon the committee meeting-as during the annual meetings of the association. Only fellows may hold office in the association and fellows are designated by an asterisk in the list of members.)

The American Society for Testing Materials (C. L. Warwick, secretary, 1315 Spruce Street, Philadelphia, Pa.) was constituted an affiliated society. (The membership of the society includes 62 fellows of the association and the society is therefore entitled to one representative in the association council.)

. The American Society of Agronomy (P. E. Brown, secretary, Iowa State College, Ames, Iowa) was constituted an affiliated society. (The membership of the society includes 93 fellows of the association and the society is therefore entitled to one representative in the association council.)

The American Geographical Society of New York (Isaiah Bowman, director, Broadway at 156th Street, New York City) was constituted an affiliated society.

The North Carolina Academy of Science (Z. P. Metcalf, president, North Carolina Experiment Station, West Raleigh, N. C.) was constituted an affiliated academy, according to the special arrangement for the affiliation of academies. (Affiliated academies collect the association dues of those of their members who are also members of the association. They each have a representative in the association council and they are allowed to retain the entrance fees collected and one dollar of each annual dues collected. When an academy is first affiliated it receives from the association one dollar for each one of its members that have already paid to the permanent secretary association dues for the current year.)

The Maryland Academy of Sciences was constituted an affiliated academy, according to the special arrangement just mentioned.

Professor T. W. Todd, professor of anatomy, Western Reserve University, Cleveland, Ohio, was elected a member of the section committee

of Section H (Anthropology), to take the place of Dr. Berthold Laufer, resigned from the association. (The new committee member's term of office expires at the end of the 1924-25 annual meeting.)

A special committee, consisting of J. McK. Cattell (chairman), L. O. Howard, D. T. MacDougal, and B. E. Livingston, was appointed to arrange for sections C, K, L, M, and N at the Toronto meeting, this committee to cooperate with the corresponding section committees in so far as their members have been elected. It was voted that this committee should organize a committee of seven members for each of the three fields, (a) Social and Economic Sciences, (b) Engineering, and (c) Medical Sciences, each of these three committees to survey the general relations between the association and the committee's province, with the aim of securing more satisfactory representation of that field of science in the work of the association. It was recommended that the membership of these three committees include eminent scientists without regard to their membership in the association, the permanent secretary and at least one other member of the association being on each.

The question regarding the organization of the History of Science was again given careful consideration by the executive committee. The special committee that arranged the excellent program on this subject for the Chicago meeting has expressed itself as in favor of the History of Science being made the field of a new section of the association, but the consideration that this field overlaps the fields of the already existing sections has prevented the executive committee from concurring with the special committee on this point. council of the association (at its Chicago meeting) favored the organization of the History of Science as a part of Section L (Historical and Philological Sciences), not yet organized, but the special committee does not favor this arrangement. The executive committee finally concluded to suggest that a special society for the History of Science might be inaugurated and that this society might become an affiliated society of the association.

The

At the suggestion of the American Society of Zoologists, a resolution was adopted favoring the duty-free importation of scientific materials into the United States by educational and research institutions.

The executive committee expressed its regret that, owing to lack of funds, the association found it impossible to comply with a suggestion recently received from the Hall of Fame of New York University, that the association provide a bust of an eminent scientist for the Hall of Fame. Upon invitation from the chancellor, the council and the committee on the Hall of Fame of New York University, three delegates were appointed to represent the Association on the occasion of the unveiling of a tablet in honor of Louis Agassiz-a past president of the Associationthis ceremony to occur in the colonnade of the Hall of Fame, at University Heights, New York City, on May 21, 1921. Messrs. C. B. Davenport, H. F. Osborn, and E. B. Wilson were appointed.

A proposal to establish a section on the Evolution of Religion and Philosophy was given consideration and it was voted that, since the subjects referred to are already provided for by existing sections of the Association, it seems unnecessary to inaugurate a special section for them at this time."

Four new items were approved for the permanent secreary's budget for 1921, these having been omitted from the budget as approved by the council at the Chicago meeting. A statement of the entire budget follows:

[blocks in formation]
« iepriekšējāTurpināt »