NA TURE 



[June 27, 1901 



Lorentz then goes on to show the effect of the 

 motion of attracting bodies in modifying the ordinary 

 law of gravitation, and here he arrives at a remarkable 

 result. The deviations from Newton's law depend on the 

 ratios of the velocities of the bodies to the velocity of 

 light, but only on the second power of these small ratios. 

 Hereby he removes the grave difficulty first pointed out 

 by Laplace against the assumption of a propagation of 

 gravitation with a finite velocity, unless this velocity was 

 millions of tunes greater than the velocity of light. By 

 the peculiar way in which the condition of the ether is 

 disturbed by a moving ion the effect of the motion on 

 the apparent attraction is of a higher order of smallness, 

 and, in fact, so small that no arguments can be drawn 

 from astronomical data in their present degree of accur- 

 acy against the assumption. The latter result is inde- 

 pendent of the special form which Lorentz gives to this 

 theory, but holds for any electro-dynamical theory of gravi- 

 tation on similar lines. Thus it looks as if there were 

 no objection to applying this important unification to our 

 physical theories. How Lorentz's work, some of it well 

 known to every student of physics, is appreciated outside 

 the narrow limits of his own country was shown not so 

 many years ago when he received a call to the University 

 of Munich to be Boltzmann's successor, an offer which he 

 did not accept ; and again in the end of last year, when 

 physicists of all countries united in honouring him on 

 his semi-jubilee as a doctor of physics. The Hvre 

 jubilaire presented to him on that occasion contains 

 some si.xty contributions, about twenty of which are due 

 to Dutch physicists, several to Lorentz's own pupils. 



Not in the work of his pupils only do we trace Lorentz's 

 hand ; much of the work done by the Dutch physico- 

 chemical school has been to a certain e.xtent dependent 

 upon his collaboration. In the book just mentioned we 

 find this authoritatively declared by Bakhuis Roozeboom, 

 the creator, we may say, of a new branch of physical 

 chemistry, viz. the application of the phase-doctrine to 

 all kinds of equilibrium. As one of the latest applications 

 of this theory, we mention the attempted, and already 

 partly successful, disentanglement of the iron-steel pro- 

 blem by le Chatelier, Roberts-Austen, von Jiiptner, and 

 Roozeboom himself {/icitschrift fiir physik. Cheinie). 

 This application is instructive in showing how purely 

 theoretical investigations may suddenly begin to bear 

 upon highly practical problems and be applied for indus- 

 trial purposes. 



Roozeboom's pioneer work was carried out when 

 still in the laboratory of the Leyden University. He is 

 now at Amsterdam as van 't Hoff's successor. In his 

 laboratory we find, working on independent lines, one of 

 van 't Hoff's pupils. Dr. E. Cohen. Of the many 

 investigations carried out by Dr. Cohen none is of more 

 general interest than that on the enantiotropy of tin, 

 partly carried out in conjunction with Dr. van Eyk. 

 Tin — the white metal as we use it —has been known 

 frequently, under the influence of intense cold, to 

 change its condition completely by turning into a grey 

 modification of lower specific gravity. This fact was 

 known to the ancients, and the literature on the subject 

 which the authors took the trouble to bring together 

 forms quite a bulky collection. Nobody had succeeded 

 so far in clearing up the chaos which surrounded the 

 phenomenon and its e.xplanation ; this has now been 

 done in the papers referred to. It appears that the 

 change from white into grey tin is a reversible pheno- 

 menon, the transition temperature being 20^ C. ; this 

 point was determined both with the dilatometer and 

 electrically by the modern method of transition-cells. 

 The transformation of white into grey tin goes on with 

 increasing velocity the lower the temperature down to 

 -50' C, after which it decreases rapidly. The exist- 

 ence of a maximum in the rate of transformation is in 

 accordance with what occurs in the transformation of 

 NO. 1652, VOL. 64] 



solids and liquids, e.g. the solidification of an under- 

 cooled liquid (Tammann). The velocity is increased (i) 

 by the addition of a little grey tin at the beginning ; 

 (2) by the addition of pink-salt ; (3) by exposing the tin 

 to the low temperature for a long period, or by alter- 

 nately cooling and warming it. Above 20^ the grey tin 

 is transformed into the white modification with very 

 rapidly increasing speed the higher the temperature. 

 Measurements have been made up to 40^ 



From the above experiments it appears that the whole 

 of our tin-world, except on a few exceptionally warm 

 days, is in an unstable condition. Dr. Cohen is now 

 trying to establish the existence of similar transition- 

 points for other metals. 



\'an Bemmelen's recent work on absorption and the 

 properties of jellies is looked upon both by chemists and 

 by physiologists as fundamental. In his researches on 

 jellies he has struck out a new line in making accurate 

 determinations of the relation between the vapour pres- 

 sure of the jelly and its composition. One of the several 

 new points discovered in that manner is that jellies, when 

 taken through cyclic transformation, show hysteresis- 

 phenomena, a circumstance which would not occur if the 

 equilibrium between the jelly substance and the water 

 was of a purely thermodynamical character, in which 

 case the phase-rule with its consequences would hold. 

 The equilibrium in the jelly depends upon its history, 

 which IS in accordance with the hypothesis that capillary 

 forces are at work. Van Bemmelen looks upon a jelly as 

 a system of two phases — a solid mixture of the colloid 

 and water, and, embedded in the interstices of this 

 mixture, water. In some jellies this solid part shows 

 remarkable sudden transformation into a modification 

 of different composition, but there is no indication 

 of the existence of hydrates. It will interest the reader 

 to hear that Prof. Bemmelen, having recently reached 

 the age of seventy, has become a " professor emeritus " 

 of the Leyden University. In the light of his recent 

 experimental work there is some humour in the Dutch 

 law considering a man of seventy unfit for a professor- 

 ship. Van Bemmelen is succeeded by Schreinemakers, 

 who may be described as Roozeboom's aller-ego (I am 

 speaking from a scientific point of view). 



Each country has its own bread, its own type of boots, 

 its own characteristic music — can the same be said with 

 regard to contemporary science ? Looking broadly at 

 the nature of the scientific work which is undertaken in 

 different countries, and the manner in which the work is 

 carried out and put before the public, we observe differ- 

 ences which are the natural manifestations of national 

 characteristics. At the same time, these differences are 

 chiefly external, superficial. No science, not even any 

 special branch of a science, is now the property of any 

 one nation. What appears to direct the exertions of the 

 men of science of a country along particular lines more 

 than national character is the influence of the few 

 eminent men which the country is fortunate enough to 

 possess. This influence in a small country like Holland 

 is obvious even to the casual observer. 



The origin of the young Dutch school of chemists is no 

 doubt to be traced to van 't Hoff. In the same way we 

 mijfht speak of a Dutch school of which van der Waals 

 is the origin. Those who want to acquaint themselves 

 with the work done recently in this branch of physics are 

 referred to the new edition of van der Waals' book on 

 the continuity of the liquid and gaseous conditions. 

 (German. Leipzig : J. A. Barth, 1900.) It is unnecessary 

 to say anything of the first volume, which is a reprint of 

 the former edition, and a translation of which has been 

 available for several years. The second volume which 

 has been added to the book contains van der Waals' 

 theories of mixtures of two substances in the liquid and 

 gaseous conditions. First of all we find a reprint of 

 van der Waals's paper of 1890 in the A>\hives Nierland- 



