stance in a manner as simple and straightforward as possible so as to give the reader some help towards an understanding of the profound changes which modern researches have brought about in the fundamental ideas and theories of physics; and, of course, in a brief discussion of this subject it is necessary to assume that the reader has considerable knowledge of classical physics and that he knows something of the principle of relativity and a little of the quantum hypothesis.

The first really effective method to be employed in the physics was the method of mechanics. This method was founded by Galileo and Newton, and, as the method was developed and more and more successfully applied, it came more and more to dominate the philosophy of physics, until, about the middle of the nineteenth century, the "mechanical conception," as Planck briefly calls it, was generally believed to be an adequate basis for the analysis of all the phenomena of nature; the "mechanical conception" aimed to explain everything in terms of motion; the "mechanical conception" is the view that all phenomena can be reduced to movements of particles or elements of mass.

The discovery of the principle of the conservation of energy (which was at first thought to be a purely mechanical principle) tended to strengthen the "mechanical conception" and the development of the kinetic theory of gases was looked upon as a sample of the unlimited conquests which the "mechanical conception" was destined to make. The latter part of the nineteenth century was the Golden Age of the "mechanical conception."

An interesting consequence of the complete dominance of the "mechanical conception" in the philosophy of physics during the latter part of the nineteenth century was a reaction against the widespread acceptance as ultimate realities of such mechanical pictures as that afforded by the kinetic theory of gases, and this reaction was most effectively voiced by Ernst Mach. There was no definite experimental knowledge of the atom fifty years ago; the atom was only an idea at that time, and the proud philosophy of the "mechanical conceptionists" drove many physicists back to a notion of reality as old as Greek philosophy; and some philosophers like Ernst Mach placed what seems to us now too great an emphasis on this old point of view, namely, the point of view that nothing is real but our sense perceptions and that all science and all philosophy is an economic adaptation of our ideas to our perceptions, an adaptation growing out of our struggle for existence. This economic point of view can hardly explain a

Newton or a Faraday, and Planck points out that it seems to be incompatible with the most important characteristic of the sciences, namely, the progressive attainment of a more and more general and unified point of view, which, while being kept in accord with experiment, becomes more and more nearly independent of the individuality of separate intellects, more and more nearly free from purely human bias, more and more nearly non-anthropomorphic.

Nevertheless the "mechanical conception" was a strong philosophy and under its stimulus important scientific work was done and some results of permanent value obtained. Planck mentions the kinetic theory of gases as one of these valuable results. Indeed the kinetic theory of gases is of very great value, although it is based on postulates which ascribe purely mechanical properties to the atom, whereas we have now renounced the purely mechanical conception of the atom.

The method of mechanics may be said to be still retained in modern physics and to be applicable to everything in nature where irreversible processes do not exist or where irreversible processes are neglected, and the method of mechanics thus widely used can be defined as including everything that conforms to and falls under the principle of least action; but the method of mechanics so defined, which Planck calls the method of dynamics, is by no means the same thing as the "mechanical conception" because in many cases it is independent of any knowledge of or any postulate concerning things or substances or particles which move. In particular it includes in its realm such things as electromagnetic disturbances (light) without requiring the existence of the ether, and it is entirely in accord with the principle of relativity.

It is apparently absurd to speak of a method as a mechanical method or as dynamics (after Planck) when there is no thought of motion of concrete things but at best only motion of energy (as in the case of light); but the method, in its mathematical aspects, in the kind of correlation which it accomplishes and in the kinds of measurements involved in its experimental researches, is the same old method of mechanics.

The reader will be left, as it were, in a mental vacuum by the above reference to the principle of least action as the thing which characterizes the method of mechanics, and it needs to be pointed out that the most advanced students of mathematical physics are but little better off than the reader in this respect, for no one as yet has any intuitive appreciation of the principle of least action nor any concep

tual insight into its meaning. The mathematical physicist only knows how to formulate the principle mathematically and how to derive its consequences. The principle of least action applies to all mechanical phenomena, to all electromagnetic phenomena (including light) and to all thermal and chemical phenomena; but it fails in all these fields when there is any irreversible action. Because of this failure of the principle it is better to say that it is useful in correlating mechanical, electromagnetic, thermal and chemical effects when the accompanying irreversible action is negligible. All these effects are highly idealized when irreversible action is ignored because every phenomena in nature is accompanied by some irreversible action, and, of course, irreversible action is very much in evidence in many thermal and chemical phenomena.

Another method in physics, the method of thermodynamics, overlaps the method of mechanics, but goes beyond the method of mechanics inasmuch as it recognizes the existence of irreversible or sweeping processes in nature; but the method of thermodynamics has nothing to do with irreversible or sweeping processes themselves, but only with their results, and indeed with only one result, namely, the increase of entropy.

Another method in physics is the atomic method, or atomics, as it is often called. It is certainly true that atoms themselves are now the objects of observation and measurement in the laboratory, but only when the fourth method, the statistical method, as described below, is used. The great theoretical structure which is called the atomic theory, especially that branch of it which is called statistical mechanics (Gibbs) of which the kinetic theory of gases is a special case, is based even now on postulates; for no one could maintain that our real knowledge of atoms is of the kind that could be used as a foundation for any elaborate mathematical structure. The atomic method is the building up of elaborate pictures or conceptions of physical conditions and things, and its chief function is to make physical conditions and things intelligible or thinkable. The kinetic theory of gases, as it exists in the mind of a physicist, is pretty nearly a working model of a gas, and it enables the physicist to "see" the properties of a gas as effectively or even more effectively than he could see them in an actual working model.

A fourth method in physics is the statistical method. The best examples of the use of this method in the laboratory are, perhaps, Perrin's experimental studies of the Brownian motion and Rutherford's experimental studies of the scattering of alpha and beta rays. The statistical method as used in the kinetic theory of gases and in statistical mechanics is a purely

theoretical structure and it belongs to the atomic theory, whereas by "the" statistical method we mean the laboratory study of actual erratic things and the interpretation of the observed results by the use of the theory of probability.

The characterization of physics in terms of methods seems to be more significant than the older subdivision of physics into branches according to subject-matter. Thus mechanics, hydrostatics, hydraulics, heat, optics, acoustics, electricity and magnetism are the old branches of physics, and the boundaries between these branches are rapidly disappearing with the advancement of physics, in fact, chemistry can no longer be thought of as a distinct branch of physical science. The branches of physical science grow less and less distinct as physical science develops, but the methods as above enumerated and briefly described are being more and more clearly recognized as distinct methods; and, what is even more important, every one of these methods has been more and more strengthened (in the field to which the method is really applicable) by modern discoveries. Thus Maxwell's theory has very greatly strengthened the dynamic method in the study of light although the electromagnetic theory of light is not a mechanical or dynamic theory in the older narrow meaning of these terms, and the altered points of view which have come from the principle of relativity have strengthened the method of dynamics.

Profound changes in our so-called fundamental ideas in physics have come about in recent years because of two things, namely, (a) an increasingly clear appreciation of the significance of irreversible actions in nature has led us to recognize definite limitations to the method of mechanics (Planck's dynamics), for an irreversible process is beyond the range of the mechanical method, and (b) the principle of relativity has modified our ideas of time and space and has extended the idea of energy to include the idea of mass; but these changes in our so-called fundamental ideas seem to be merely formal or at most these changes seem to have eliminated only what is non-essential from our fundamental ideas, leaving our methods essentially unaltered; but the quantum hypothesis seems to strike more deeply.

The quantum hypothesis denies the principle of continuity as used throughout the method of mechanics. Atomic processes take place by jumps so that the idea of time as a continuous flux is brought into question, and if time as a continuous flux is objectively non-existent then the whole structure of theoretical dynamics must be purely idealistic and at best only applicable to large scale phenomena. Indeed, the atomic theory itself raises the presumption that continuous space is an idea, not a physical fact, as

was pointed out by Riemann many years ago, and thus the purely idealistic character of theoretical dynamics is again indicated.

The whole of statistical mechanics, which includes the kinetic theory of gases, is a theoretical structure based upon purely mechanical postulates concerning atomic action whereas the quantum hypothesis rules out the purely mechanical conceptions of atomic action and it seems therefore that the quantum hypothesis is likely to lead to profound changes in the atomic method.

As stated above the methods of physics have remained almost wholly unchanged by modern developments, and, although the principle of continuity is in danger of being thrown out by the quantum hypothesis, the other principles of physics seem to be altered by being made more general. (a) The principle of the conservation of energy still stands, but the principle of the conservation of man has become a part of it. (b) The principle of the conservation of momentum retains its validity in a decidedly widened field. (c) The second law of thermodynamics is untouched. Many men who hold a principle narrowly seem to feel that the principle is destroyed by a change which on careful scrutiny turns out to be only a generalization of the principle.

WM. S. FRANKLIN MASSACHUSETTS INSTITUTE OF TECHNOLOGY

SPECIAL ARTICLES

HIGH VOLTAGE CATHODE RAYS OUTSIDE

THE GENERATING TUBE1

LENARD succeeded in getting electrons from a cathode-ray tube out through a thin metal window into the air. The voltage employed was that necessary to produce a 3 cm. spark between small spheres. The window consisted of a piece of aluminum foil 0.00265 mm. thick and 1.7 mm. in diameter.

With a specially designed hot cathode, high vacuum tube, it has been found possible to operate with as much as 200,000 volts and several milliamperes, using a window as large as 8 cm. in diameter. The general design of this tube would seem to permit of the use of still larger windows and higher currents.

The maximum range of the electrons in the air in front of the window has been measured approximately by the luminescence of lime. It is a linear function of the voltage applied to the tube and for an aluminum window 0.0254 mm. thick, is given by the equation:

Range (cm.) = 0.254 × Kilovolts (max.) -17.8. The 1 Preliminary communication.

lowest peak voltage at which there is appreciable intensity in front of and close to the window is 70 kilovolts, and the maximum range at the highest voltage used, 250 kilovolts, is 46 cm.

The luminosity of the air in the path of the discharge is very beautiful, especially at the higher voltages, where, due to scattering, the beam is seen to spread out and bend around until it finally extends more than half as far back of the window as it does in front of it. The appearance is then that of a solid ball of purple glow with its center a little front of the window.

Calcite crystals, upon being rayed, fluoresce strongly in the orange and remain highly luminous for several hours after raying. In addition to this they may show bright bluish white scintillations. These have been observed while the crystal is undergoing bombardment and for as long as a minute after raying. By slightly scratching the rayed surface of the crystal with any sharp instrument, the scintillations may be produced for as long as an hour after raying.

The area in the neighborhood of a scintillation loses all of its luminosity as the scintillation takes place and then appears dark against the bright orange background.

Under the microscope the spot where the scintillation took place is marked by a little crater with many tiny canals leading into it.

The high voltage electrons from this tube when brought into gases cause various reactions somewhat as Lind finds for radium emanation. The quantity relations are such that large amounts of the resulting substances may be made. For example, with such a tube there has been produced from acetylene relatively large quantities (grams) of a yellow compound which resembles the product previously obtained in small quantities both from the corona discharge in acetylene and from the use of radium emanation.

Many liquids and solids also undergo marked chemical changes under the influence of the high speed electrons. For example, castor oil changes rapidly to a solid material. Crystals of cane sugar turn white in color and, upon subsequent gentle heating, evolve considerable quantities of gas. An aqueous solution of cane sugar becomes acid to litmus upon being rayed.

The effect on organized tissues is very pronounced, as may be seen from the following examples.

When a portion of the leaf of the rubber plant (Ficus Elastica) is rayed with 1 milliampere for as long as 20 seconds, the rayed area becomes immediately covered with white latex, as though the cell walls had, in some way, been ruptured. An exposure of as little as 0.1 milliampere for 1 second produces a visible color change with subsequent drying out of the

rayed area to a depth corresponding to the penetration of the rays.

The ear of a rabbit was rayed over a circular area 1 cm. in diameter with 0.1 milliampere of current for 0.1 second. Within a few days the rayed skin became deeply pigmented and the hair came out. It was not until seven weeks after the treatment that new hair appeared.

A second similar area was rayed with 1 milliampere of current for 1 second. After several days a scab formed over the rayed area and a few days later the scab came off taking the hair with it. Two weeks later a profuse growth of snow white hair started and soon became much longer than the original gray (drab colored) hair.

A third area on the ear was rayed with 1 milliampere for 50 seconds. In this case a scab developed on both sides of the ear and these scabs later fell out leaving a hole in the ear. The periphery of this hole was at first devoid of hair but is now covered with a growth of snow white hair.

Fruit flies, upon being rayed for a small fraction of a second with 1 milliampere, instantly showed almost complete collapse and in a few hours were dead.

Bacteria have been rayed and an exposure of 1/10 second has been found sufficient to kill even the highly resistant spores of b. subtilis.

The phenomena of luminescence, phosphorescence, thermo-luminescence and change of color which take place as a result of electron bombardment from the tube are very striking and easily demonstrated, and many substances which could not be brought into a vacuum can be subjected to electron bombardment in this way.

Detailed reports of this work are now being prepared for publication.

W. D. COOLIDGE

RESEARCH LABORATORY, GENERAL ELECTRIC COMPANY, SCHENECTADY

THE TRANSFER OF TOBACCO AND TOMATO MOSAIC DISEASE BY THE PSEUDOCOCCUS CITRI1

AMONG Several thousand tobacco and tomato seedlings in the greenhouse during a year and a half, in no instance was there observed spontaneous mosaic disease. Almost all these plants were repotted during this period, many were cut back and over two hundred were injured and injected with non-mosaic materials. These observations support the opinion of Allard and others that mosaic disease in these species 1 I am indebted to Mr. Peter P. Haselbauer for his technical assistance and for his hearty cooperation.

does not arise spontaneously in healthy growths. They are not, however, in agreement with the belief of Woods and of Heintzel that the active agent is an enzyme present in all healthy tobacco plants, or of Hunger and of Sturgis, among others, that mosaic is a physiological disease which arises as a result of unfavorable conditions. In addition, three hundred plants, grown from seeds obtained from a tobacco growth that had had this affection for at least six months, remained healthy; thus we have demonstrated, as others have done previously (Allard, Gardner and Kendrick), that the disease is not seed-borne.

Recently-in June, 1925-an infestation occurred in the greenhouse with the Pseudococcus citri (family Coccidae; sub-family Dactylopinae). These "mealy" bugs were found not only on the normal, but also on the mosaic plants, all having been kept under the same roof. About one month after the insects appeared, twenty of fifty tobacco plants, uninoculated or uninjured, but infested with the bugs, showed typical mosaic disease. Twenty-four normal tomato plants, similarly infested, were removed from the greenhouse and replanted in a field. After a month all developed into typical mosaic growths. On the other hand, thirty-six tomato plants free from Pseudococcus citri remained normal after transfer to the field. Insecticides were applied and the greenhouse was freed from these insects. At least five hundred tobacco and tomato plants, forty of which were injured by thoroughly scratching two leaves of each, were subsequently grown there. All these remained healthy. Finally, the pseudococci were removed from mosaic tissues on which they had been feeding and three to five were gently transferred to each of nine tomato and five tobacco plants. Of the former, seven, and of the latter, three exhibited typical mosaic disease after incubation periods of from ten to twenty-one days.2

It appears, therefore, that the Pseudococcus citri is a vector of the mosaic virus.

To summarize, it may be stated that spontaneous mosaic does not occur in healthy or injured tobacco or tomato, or in these plants injected with non-mosaic materials; nor is the disease seed-borne. If the affection occurs under these conditions, care should be taken to eliminate as a factor the Pseudococcus citri, which is a carrier of the mosaic virus in greenhouses, in the same way as are the Aphididae in the field. PETER K. OLITSKY

THE ROCKEFELLER INSTITUTE

FOR MEDICAL RESEARCH

2 The incubation period, after injection of mosaic virus, is generally about ten days. Concentration of the virus, however, to one tenth of its original volume shortens this period to five days.

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

THE regular fall meeting of the executive committee of the association was held at the Cosmos Club in Washington, on October 25, in three sessions. The following paragraphs summarize the business transacted. The forenoon session convened at 10:10, with the committee chairman, Dr. J. McK. Cattell, in the chair. The following members were present: Cattell, Fairchild, Humphreys, Kellogg, Livingston, Moulton, Noyes, Pupin, Ward. Absentees were Duggar and Wilson. By invitation Dr. Rodney H. True, secretary of the committee of one hundred on scientific research, was in attendance.

1. The permanent secretary's annual report on the affairs of the association was presented and accepted. It will be published in SCIENCE.

2. It was reported that the permanent secretary's office is arranging to have one or more representatives of the association in each state, to make prompt reports on legislative and other occurrences and activities that may tend to advance or retard the progress of science and education. It is planned that reports, as they come in, are to be digested and published in SCIENCE, for the information of members and others interested in the advancement of knowledge. The divisions of the association and the affiliated academies have aided in selecting the representatives for their respective states. The executive committee requested the permanent secretary to ask these representatives to report from time to time important movements or actions that are favorable to the progress of science and education as well as unfavorable ones.

3. A plan was approved by which persons in arrears for membership dues may at any time become life members by paying the life-membership fee ($100), without also paying up their arrearage. Each such member is to be reinstated and his life membership is to date from the receipt of the fee.

4. It was voted that new members who join the association during the current year may omit the payment of the regular five-dollar entrance fee if they become life members, paying the regular life-membership fee. New members may be credited with payment of $10 towards the life-membership fee if they pay the entrance fee and the first annual dues on joining and if they pay the remaining ninety dollars at any subsequent time during the year. Any member in good standing may become a life member at any time by paying ninety-five dollars, the annual dues already paid for the current year being credited to his account as regards life membership.

5. The committee approved a general campaign for an increased number of life members. (Forty-one new life members were enrolled in the fiscal year ended September 30 last.)

6. The executive committee recommended to the council the following appropriations for the current fiscal year, from the available funds in the treasury. This recommendation will be brought before the council at the Kansas City meeting.

a. To the American Association Table at the Naples Zoological Station

b. To the International Annual Tables of Physical, Chemical, and Technological Data

c. To the American Institute of Sacred Literature

......

$500

$200

$60

d. To individual grants for research, to be allotted by the Committee on Grants $3,000 7. The executive committee appropriated the sum of $500 from the available funds of the treasury, to care for the expenses of the Committee of One Hundred on Scientific Research for the current year.

8. It was voted that Dr. Henry B. Ward be requested to visit Kansas City and be given charge of certain features of the preparations for the Kansas City meeting.

The afternoon session convened at 2:30, with Dr. Cattell in the chair and the following members present: Cattell, Fairchild, Kellogg, Livingston, Moulton, Noyes, Pupin, Ward. Dr. True was present by invitation.

9. It was voted that the association heartily approves suggestions presented by President Pupin, that steps be taken as far as possible to further cooperation between the engineering societies and the association. According to these suggestions, Dr. J. McK. Cattell (chairman of the executive committee of the association) and Dr. Ira N. Hollis (past vice-president for the engineering section) were named as representatives of the association to work toward this end with representatives of the four Founder Societies in engineering.

10. President Pupin explained a plan to have an evening session at the Kansas City meeting to emphasize the relations of engineering to the other science groups in the association, with the hope that Mr. Herbert Hoover, secretary of commerce, may accept an invitation to address the association on that evening. The committee heartily approved the suggestions made by President Pupin and extended to Mr. Hoover a very cordial invitation to attend the Kansas City meeting and deliver an evening address. The permanent secretary was in

structed to transmit this invitation to Mr. Hoover.

11. The auditor of the association, Dr. Robert B. Sosman, was named as one of three members, any two of whom are authorized to have access to the safetydeposit drawer of the Association in the American Security & Trust Company in Washington. (The other two, already named, are the treasurer and the permanent secretary. It is required that two of these three members shall present themselves whenever access to the drawer is desired.)

12. The permanent secretary was authorized to complete the roll of the prize award committee for the Kansas City meeting.