Search

To discuss Einstein’s principle of relativity here at Gottingen, where Minkowski was active, seems to me a particularly welcome task. The significance of this principle can be illuminated from several different angles. We will not speak here of the mathematical aspect of the question, which was given such a splendid treatment by Minkowski, and which was further developed by Abraham, Sommerfeld and others. Rather, after some epistemological remarks about the concepts of space and time, the physical phenomena that may contribute to an experimental test of the principle shall be discussed. The principle of relativity claims the following: If a physical phenomenon is described by certain equations in the system of reference then a phenomenon will also exist that can be described by the same equations in another system of reference Here the two systems of reference are connected by relations containing the speed of light and expressing the motion of one system with a uniform velocity relative to the other. If observer is located in the first, and in the second system of reference, and each is supplied with measuring rods and clocks at rest in his system, then will measure the values of and the values of where it should be noted that and can also use one and the same measuring rod and the same clock. We have to assume that when the first observer somehow hands his rod and clock over to the second observer, they automatically assume the proper length and the proper rate so that arrives at the values from his measurements. Either one will then find the same value for the speed of light, and will quite generally be able to make the same observations. x y z t , , ,

n/a

H.A. Lorentz: Sketches of his Work on Slow Viscous Flow and Some Other Areas in Fluid Mechanics and the Background Against which it Arose H.K. Kuiken. A General Theorem on the Motion of a Fluid with Friction and a Few Results Derived from It H.A. Lorentz. Reinterpreting the Basic Theorem of Flagellar Hydrodynamics J. Lighthill. Helical Distributions of Stokeslets Sir James Lighthill. Computation of Periodic Green's Functions of Stokes Flow C. Pozrikidis. Integral Formulation to Simulate the Viscous Sintering of a Two-Dimensional Lattice of Periodic Unit Cells G.A.L. van de Vorst. Image of a Point Force in a Spherical Container and its Connection to the Lorentz Reflection Formula C. Maul, Sangtae Kim. Axisymmetric non-Newtonian Drops Treated with a Boundary Integral Method E.M. Toose, et al. Ciliary Propulsion, Chaotic Filtration and a "Blinking" Stokeslet J.R. Blake, S.R. Otto. The Lorentz Reciprocal Theorem for Micropolar Fluids H. Brenner, A. Nadim. Motion of a Solid Sphere in a General Flow Near a Plane Boundary at Zero Reynolds Number R.G. Cox. Lorentz Theorem on the Stokes Equation H. Hasimoto. A Second Kind Integral Equation Formulation for the Low Reynolds Number Interaction Between a Solid Particle and a Viscous Drop H. Power. The Use of Stokeslets to Describe the Arbitrary Translation of a Disk Near a Plane Wall A.M.J. Davis. Asymptotics Beyond All Orders for a Low Reynolds Number Flow J.B. Keller, M.J. Ward. Stokes Flow Due to Infinite Arrays of Stokeslets in Three Dimensions N. Liron. Thermocapillary Mobility of Bubbles and Electrophoretic Motion of Particles in a Fluid B.U. Felderhof.

n/a

When, some months ago, the secretary had the kindness to ask me to deliver this lecture, I was glad, for various reasons, to accept the invitation. In the first place, and this would have been sufficient, because the great name of Benjamin Franklin, for whom I have always felt a deep veneration, is connected with this place. Secondly, because your Institute once did me the honour to award me the Franklin medal, which, to every man of science, is a very great distinction. I was not, at the time, able to come to Philadelphia to receive the medal but it would have been very unkind on my part, if I had not availed myself of this opportunity for expressing my thankfulness and appreciation.

(1941). 3. THE GOLDEN ORIOLE (Oriolus oriolus) IN HOLLAND. Ostrich: Vol. 12, No. 1, pp. 11-16.

n/a

n/a

n/a

they do strain the sacred writings, who there interpret these words for the measured quantities." But Cajori's "improvement" would have Newton say, "On this account, those violate the accuracy of language, which ought to be kept precise, who interpret these words for the measured quantities."16 For those who may wonder how Cajori could have altered those innocent words sacris litteris to "the accuracy of language, which ought to be kept precise," may I remind them that Cajori's alterations of Motte do not generally arise from a verbatim et litteratim confrontation of Newton's Latin and Motte's English versions. And in this case, Cajori's source was neither Newton nor Motte. He chose to replace Motte's correct and literal rendition by Thomas Thorp's, only changing the latter's "which ought to be kept sacred" to "which ought to be kept precise." 7 Each reader may frame his own joke on this travesty of "accuracy of language" which-all would agree-really "ought to be kept precise." 16 Motte-Cajori version, p. 11. though the prospectus, of which there are two copies in the library of the old Ashmolean 17 Only Vol. I of Thomas Thorp's transla- Museum in Oxford, announced that he had tion of the Principia was ever published, al- translated all three books. See n. 8 supra.

The electromagnetic theory of light which was formulated by Maxwell 2) in 1865 has since, especially through the experiments of various physicists on the specific inductive capacity of nonconducting media, acquired a high degree of credibility. Although I consider it exceedingly probable that a change in our conceptions as regards electric phenomena will lead also in some degree to an alteration in the theory of Maxwell, I still hold that its main principle, i.e., the hypothesis that vibrations of light are movements of the same character as electric currents, can hardly be questioned. It appeared therefore to me to be desirable to make a further investigation of the results of this theory which have as yet been only partially compared with experience. By this means it will not only be possible to estimate the value of the theory, but if it is correct there is also a chance that the investigation of light phenomena may advance to some extent our knowledge of the action of electricity.

n/a

When I had the honour to be invited to deliver a lecture in the Rede Foundation, I thought I might perhaps present to you a brief review of the electromagnetic theory of your great physicist James Clerk Maxwell. The choice seemed the more appropriate as it is now exactly fifty years ago that the work which raised him at once to the very first rank of investigators of all ages, the Treatise on Electricity and Magnetism, was published. In this work it was proved beyond all doubt that electric and magnetic actions can be conceived as being transmitted through a medium and the theory was crowned by the wonderful revelation that light is an electromagnetic phenomenon.

Terwijl ik het als een voorrecht beschouw, een bijdrage tot dit Gedenkboek te mogen leveren, scheen mij aanvankelijk, daar ik geheel buiten de muzikale wereld sta, de keus van een onderwerp moeilijk. Na eenig zoeken meen ik intusschen iets gevonden te hebben, dat hier misschien niet misplaatst is; een korte uiteenzetting van de natuurkundige verklaring der tonen van de Aolus-harp en van andere soortgelijke geluiden zal, dunkt mij, ook bij musici belangstelling kunnen vinden.

In my „Versuch einer Theorie der electrischen und optischen Erscheinungen in bewegten Korpern” (Leiden, 1895)2) I examined the propagation of light in transparent bodies having a constant translation with velocity p, the aether being supposed to remain at rest, and tried to find, in how far optical phenomena may be affected by this motion. In the case of the rotation of the plane of polarization in optically active substances, I had to leave the question undecided. Indeed, the relation between the electric force E and the electric moment M, to which I was led by certain general principles (linear form of the equations, isotropy of structure and reversibility of the motions) does not only contain the coefficient j, which determines the rotation in the quiescent medium; there is besides a second coefficient k, which is multiplied by the velocity p, and whose ratio to j I could not determine, because I wished to refrain from special hypotheses as to the mechanism of the phenomenon.

Laat ik er vooreerst op wijzen, dat, zoo het mij gelukt is, iets tot den vooruitgang der natuurkunde bij te dragen, ik daarvoor ook ruimschoots den tijd heb gehad; in de lang vervlogen dagen, toen mijn tegenwoordige promotor en ik, in zoo aangename samenwerking, te Leiden voor de collegeproeven zorgden, was ik al een twintig jaar aan het werk geweest. En niet alleen werd mij de tijd gegund; ik heb ook aan alle zijden aanmoediging en opwekking gevonden bij leermeesters, oudere en jongere vakgenooten, van wie vele goede vrienden voor mij waren en nog zijn, en bij voortreffelijke leerlingen.

In pursuance of his important researches on gravitation Einstein has recently attained the aim which he had constantly kept in view; he has succeeded in establishing equations whose form is not changed by an arbitrarily chosen change of the system of coordinates2). Shortly afterwards, working out an idea that had been expressed already in one of Einstein’s papers, Hilbert 3) has shown the use that may be made of a variation law that may be regarded as Hamilton’s principle in a suitably generalized form. By these results the “general theory of relativity” may be said to have taken a definitive form, though much remains still to be done in further developing it and in applying it to special problems. It will also be desirable to present the fundamental ideas in a form as simple as possible.

It is a great honor to me to have been requested to address you on this memorable occasion and I have many good reasons for being interested in to-day's proceedings. In the first place, I have been so kindly and warmly welcomed by the scientific men of the institute that I feel almost as if I belonged to them and as if I also were going to have a share in the facilities for scientific research that have now been put at their disposal.

Onder de hulpmiddelen die de natuurkunde den medici en biologen verschaft heeft, mag het mikroskoop bovenaan worden gesteld; elke verbetering hiervan heeft een oogst van nieuwe ontdekkingen ten gevolge gehad, en door de grens waartoe het vermogen van het mikroskoop kan worden opgevoerd, wordt in menig biologisch onderzoek het bereikbare aangegeven. Het zal daarom, naar ik hoop, aan het doel dezer vergadering beantwoorden, wanneer ik u verzoek, uwe aandacht te mogen bepalen bij de laatste uitbreidingen van het veld van mikroskopisch onderzoek; eenige opmerkingen over de beteekenis van optische verschijnselen voor ons inzicht in den bouw der materie zullen zich daarbij als van zelf aansluiten.

n/a

The discussion of some parts of Einstein’s theory of gravitation2) may perhaps gain in simplicity and clearness, if we base it on a principle similar to that of Hamilton, so much so indeed that Hamilton’s name may properly be connected with it. Now that we are in possession of Einstein’s theory we can easily find how this variation principle must be formulated for systems of different nature and also for the gravitation field itself.

On trouve, vous le savez, dans les annuaires astronomiques les donnees qui permettent d’indiquer, pour un corps celeste quelconque, la position qu’il occupera a un moment donne. Prenons, par exemple, une etoile fixe, une etoile que peut-etre on ne peut apercevoir a l’œil nu: vous pouvez savoir d’avance dans quelle direction il vous faudra braquer le telescope pour la voir a un moment arbitrairement choisi de la soiree. Si, apres avoir donne au telescope la direction voulue, vous appliquez l’œil a l’oculaire, quelques instants avant le moment indique, vous verrez bientot apparaitre l’etoile a l’un des bords du champ qu’elle va traverser. Exactement, a la seconde attendue vous la verrez obscurcie un instant par un des fils tenus tendus au milieu du champ; le pronostic de l’annuaire se trouvera ainsi confirme.

Wenn ich in dieser Stunde Ihr wohlwollendes Interesse auf einige Probleme der heutigen Physik lenke, so bietet sich mir eine grosse Auswahl dar. Zahlreich sind ja die Wege, auf welchen wir versuchen, die Naturerscheinungen unserem Geiste naher zu bringen; einige sind sicher und fuhren geradeswegs auf das Ziel hin; andere schlangeln sich um unuberwindliche Schwierigkeiten oder sind nur auf kurze Strecken durch kuhne Bahnbrecher angelegt. Individuelle Eigenschaften und Neigungen bestimmen fur jeden Forscher die Wahl; der eine wird mit Vorliebe das Gebiet unserer Kenntnisse durch neue Entdeckungen erweitern, der andere lieber das bereits gewonnene Terrain bearbeiten und ebnen.

Wenn man durch theoretische Betrachtungen den Einflus zu bestimmen versucht, den eine Translation, wie sie z. B. alle Systeme durch die jahrliche Erdbewegung erfahren, auf elektrische und optische Erscheinungen ausuben konnte, so gelangt man in verhaltnismasig einfacher Weise zum Ziel, solange nur solche Grosen betrachtet zu werden brauchen, die proportional der ersten Potenz des Verhaltnisses der Translationsgeschwindigkeit w zur Lichtgeschwindigkeit c sind. Falle, in denen Grosen von zweiter Ordnung, also von der Ordnung \(\frac{{{w^2}}}{{{c^2}}}\), wahrnehmbar sein konnten, bieten mehr Schwierigkeiten. Das erste Beispiel dieser Art ist Michelsons wohlbekannter Interferenzversuch, dessen negatives Ergebnis Fitzgerald und mich zu dem Schlusse fuhrte, das die Dimensionen fester Korper sich infolge ihrer Bewegung durch den Ather ein wenig andern.

Fur das Verstandnis der Eigenschaften der Materie und die Ergrundung des Zusammenhanges zwischen verschiedenen physikalischen Wirkungen sind diejenigen Erscheinungen von groser Bedeutung, bei welchen sich ein Einflus auserer Einwirkungen auf die optischen Eigenschaften der Korper kundgibt. Diese Einwirkungen konnen mechanischer, thermischer, elektrischer oder magnetischer Art sein. So werden im allgemeinen die optischen Konstanten durch ausere Krafte und durch Erwarmung oder Abkuhlung geandert, der Brechungsindex eines durchsichtigen isotropen Korpers z. B. in solcher Weise, das er in erster Annaherung als eine Funktion der Dichte betrachtet werden kann. Einseitiger Druck oder Zug, wodurch die Isotropie, falls sie ursprunglich vorhanden war, verloren geht, hat bei festen Korpern eine Doppelbrechung zur Folge, und ahnliches beobachtet man bei gewissen Flussigkeiten, wenn ihre Schichten sich ubereinander verschieben. Ferner hat Humphreys durch seine Beobachtungen uber die Verschiebung der Spektrallinien von Gasen bewiesen, das Druckerhohung die Lichtemission modifizieren kann, und hat man andere Verschiebungen, die, dem Dopplerschen Prinzip gemas, auf eine Bewegung der leuchtenden Teilchen zuruckzufuhren sind, in manchen Fallen wahrgenommen und zu wichtigen Schlussen verwertet.

Je suis heureux d’avoir l’occasion de dire quelques mots dans cette grande et belle ceremonie, de prononcer quelques paroles en l’honneur d’Augustin Fresnel, le grand physicien, le fondateur de l’optique moderne. Je vais exprimer, j’en suis sur, les sentiments de tous mes confreres, de tous les physiciens etrangers, de ceux qui sont presents ici, comme de ceux qui dans tous les pays du monde pensent aujourd’hui avec nous a Augustin Fresnel.

Directeuren onzer Maatschappij hebben gewenscht dat heden, nu zij en de leden voor de eerste maal na het verlies van onzen betreurden Bosscha bijeen zijn, een woord van dankbaarheid en waardeering aan zijne nagedachtenis zou worden gewijd. Aan dat verlangen, dat bij ons allen weerklank vindt, gevolg gevende, zal ik trachten in Uwe herinnering terug te roepen wat Bosscha voor de wetenschap en voor onze Maatschappij geweest is.

It was remarked some years ago by Kretschmann 2) that from observations solely concerning the course of rays of light and the motion of material particles, the values of the potentials g ab which characterize a gravitation-field can be so far deduced that only a constant factor remains undetermined. He showed, in fact, that, if two sets of values g ab and ḡ ab are in agreement with these observations, the ratio ḡ ab /g ab must be the same for all suffixes a and b, and independent of the coordinates.

The illustrious founder of our society will forever occupy a prominent place in the history of physical science, not only for his experimental researches in electricity and his invention of the lightning rod, but also for his theoretical views. Franklin tried to explain all electrical phenomena that were known in his time by means of a single electric fluid, which he supposed to be present in certain definite quantities in all ponderable bodies, when in their natural or unelectrified state, and in larger or smaller quantities in positively or negatively charged bodies. The rival doctrine was that of two electric fluids, which in the days before Maxwell served as the foundation of the mathematical theory of electricity and which was adopted by those physicists who, like Riemann, Weber and Clausius, sought to account for electrostatic and electrodynamic phenomena by one fundamental law for the mutual action of electric particles.

Il y a quelques annees Einstein 2) arriva a la conclusion que tout changement dans l’energie interne e d’un corps a pour consequence un changement de la masse m, de telle sorte qu’il existe entre les accroissements δe et δm la relation $$ \delta m\frac{{\delta \varepsilon }} {{c^2 }}, $$ (I) ou c est la vitesse de la lumiere. Je me propose de deduire d’une autre facon ce theoreme remarquable et de traiter un peu en detail deux cas particuliers.