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Essai sur la Notion de Th6orie physique de Platon a GalilBe. B y Pierre Duhem. Extrait des A n d e s de Philosophie Chr6tienne. 16 X 25 cm; Pp. 143. Paris: A . H e r m a n n , 1908. Price: paper, 5 jrancs.-“ -4ccording to Plato the heavenly bodies move with a circular, uniform and entirely regular‘ motion. H e places this problem before the mathematicians: What circular, uniform and entirely regular motions must be assumed in order to account for the apparent motion of the planets? “This aim of astronomy is here presented with great clearness. This science combines circular and uniform movements in such a way as to give a resultant motion corresponding to t h a t of the stars, IThen the geometrical construction assigns to each planet a motion resembling t h a t which is actually seen, the goal of the astronomer has been reached for his h3,fiothese.r h a w acco ti )i ted )or t he # h e tz o me nu,’ ’ “Though the astronomer may he fully satisfied when the hypotheses, which he has devised, account for the phenomena, has not the mind of man a right to ask for something more? Can i t not discover and analyze some characteristics depending on the nature of the heavenly bodies? May not these characteristics enable him to point out certain fundamentals to XThich the astronomical hypotheses must necessarily conform? Ought i t not be possible to exclude certain hypotheses as not conforming to these fundamentals even though these hypotheses account for the phenomena? “ I n addition to the method o j the astronomer, so clearly defined by Plato, Xristotle maintains the existence and legitimacy of other criteria ; he calls this the incthoti of the ph~~sici;t.” “Xristotle insists t h a t the universe is spherical, t h a t the celestial bodies are solid, t h a t each one of them has a circular and uniform motion around the centre of the universe, and that this centre is occupied by the stationary earth. These are restrictions which he imposes on the hypotheses of the astronomers and he would not hesitate to reject a n y combination of movements which seemed to violate any of these conditions. H e does not impose these conditions because he believes them indispensable in accounting for the phenomena which have been observed. ilccording to him they are made necessary by the perfection of the essence from which the heavens are formed and by the nature of circular motion. IThile Eudoxius and Calippus adopt the method of the astronomer and check their hypotheses by seeing whether they account for the phenomena, Xristotle undertakes to restrict the choice of hypotheses by means of certain propositions justified by speculations on the nature of matter: his method is t h a t of the physicist.” I n this volume Duhem sketches the developments of these two points of view from the time of Plaro to t h a t of Galileo. T h e matter is of fundamental importance and the question whether the particular restrictions imposed by Aristotle are correct is one of entirely secondary importance. T h a t the probleni is not purely a n academic one is shown b y the fact t h a t Hipparchus was able to account for the apparent motion of the sun round the earth by two distinct hypotheses. Here again i t is quite unimportant t h a t we now know t h a t neither hypothesis was right. In a different form the difference of opinion between Always in the same direction.
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Plato and Aristotle is a live question to-day. Nost physicists and chemists recognize as one goal the representation of phenomena by means of a kinetic hypothesis. Others are searching-so far in vain-for some criterion which will enable them to exclude the kinetic hypothesis from the list of permissible hypotheses, quite irrespective of the success with which the kinetic hypothesis may represent the facts. Until the appearance of Svedberg’s “Studies on Colloidal Solutions,” Ostwald was unquestionably an Aristotelian. I t is not certain whether he still is or not. I n the summary Duhem says: “Many philosophers since Giordano Bruno have reproached A4ndr6Osiander bitterly for the preface which he wrote for the book of Copernicus. The advice given to Galileo by Bellarmine and by Urban VI11 has been treated with little less severity ever since i t was published. However, the physicists of our time have been more careful than their predecessors in their examination of the exact value of the hypotheses made use of in astronomy and in physics. They have seen many things change t u illusions, in spite of having been considered as certainties not very long ago. They are obliged to recognize and to declare to-day t h a t logic n-as on the side of Osiander, of Bellarmine, and of Urban VI11 and not on the side of Kepler and of Galileo; t h a t the former had understood the exact limitations of the experimental method while the latter had been confused in regard to i t . “The history of science nevertheless exalts Kepler and Galileo whom it places in the ranks of the great reformers of the experimental method, Tyhile i t does not pronounce the names of Osiander, of Bellarmine and of Urban T‘III. Is not this because those, who had a false idea of the value and limitations of the experimental method, have developed this method much more and much better than those, \Those appreciation of i t had been a t first more exact and more thorough ? ” TI-ilder D . Uaizcrojt
Trait6 de Physique. B y 0.D . C;huolsoiz. Ourrage ivaduif SILY les Editions riisse et allemaiide par E . Daraiix. Editioiz rerue et consid&ablcmeizt auginentde p a r l’.Auteur, suivie de S o f c s s11r la Phj,sique tit6oriqite par E . Cosserat et I;.Cosserat. A z c c Z L ~ CPrhface de E.-H. Anzagat. T o m e pvern ier, qi~atribincfascicide. 16 X 2 5 c m ; p p . 873-1092. Paris: A. Ifermav~17,rgo8.-This volume is devoted entirely to acoustics and while there is not as much of immediate interest to the physical chemist in i t as in some of the preceding numbers, the book contains a good deal which can be read with profit. On p. 902 we find the following general remarks on acoustics: “ T h a t part of physics vhich \ye call acoustics deals v i t h the phenomena of sound, It has some distinct peculiarities. In the first place i t is characterized b y the lack of any special hypothesis of great importance, such as the hypotheses on which rest the study of radiant energy, of heat energy or of electrical energy. The vibrations of matter, which are closely connected v i t h the phenomena of sound, are usually to be perceived by our senses. l y e can see them or feel them and we have no doubt of their reality. In so far aS acoustics is a study of a definite group of phenomena, i t approaches more closely than the other divisions of physics to t h a t ideal toviards ryhich science tends, and according to which the facts of nature are accounted for completely by the principles
