NA TURE 



533 



THURSDAY, APRIL 4, 1901. 



SPACE, ATOMS, MOLECULES AND THE 



ETHER. 



Matter, Ether and Motion. By A. E. Dolbear, Ph.D. 



English edition edited by Prof. Alfred Lodge. Pp. 



vii + 376. (London: Society for Promoting Christian 



Knowledge, 1899.) 

 La Constitution du Monde, Dynamique des Atomes. Par 



Madame Clemence Royer. Pp. xxii + 800. (Paris : 



Librairie C. Reinwald, 1900.) 

 Mutmassungen iiber das Wesen der Gravitation, den 



Elektricitdts und der Magnetismus. Von Dr. med. 



Hermann Fischer. Pp. 42. (1899.) 

 Ueber mogliche Bewegungen moglicher Atome. Von Dr. 



med. Hermann Fischer. Pp. 92. (Dresden : Hell- 



muth Henkler, 1900.) 



A QUARTER of a century ago the Society for Pro- 

 moting Christian Knowledge published a small 

 book of 125 pages on "Matter and Motion," by Prof.' 

 Clerk Maxwell, and it is interesting to reflect that the 

 necessity of adding the ether to the title of a new book 

 issued by the same publishers is largely due to the im- 

 portant modern developments of the ideas which, in his 

 more abstruse writings, the author of the original book 

 suggested. There is, no doubt, a considerable demand 

 at the present time for a book dealing in a popular way 

 with general notions about molecules and the ether ; but 

 it is desirable that, in attempting to meet this demand, 

 scientific accuracy no less than simple and popular 

 treatment should be aimed at. 



Dr. Dolbear is fortunate in having it stated conspicu- 

 ously that his book is " edited by Prof. Lodge," who in 

 his preface remarks that 



"the luminous manner in which the author deals with 

 the great problems as to the nature of electricity, mag- 

 netism and the kinetic relations between ether and matter 

 will make this book interesting and instructive to a wide 

 circle of readers." 



But even the editor is bound to admit that 



" I do not agree with all the author's statements, par- 

 ticularly that on p. 75, where he maintains that transfers 

 of energy are always from bodies having higher rates 

 of motion to those having lower rates. ..." 



An examination of the book shows that it contains 

 many statements quite as open to objection as that cited 

 by Prof. Alfred Lodge. A few extracts will give an idea 

 of the style of the book. 



On pp. 14-17 the author takes a great deal of trouble 

 to prove that we shall never be able to construct a micro- 

 scope sufficiently powerful to see individual molecules. 

 To prove this, he tries first to argue from a rather far- 

 fetched analogy between the powers of the microscope 

 and the stage-coach and the railway ; then he refers to 

 the impossibility of seeing molecules owing to their rapid 

 motions ; and finally he states that 



" there is every reason to believe that the molecules of 

 all bodies are so perfectly transparent that they could no 

 more be seen than the air, even if there were no difficulty 

 from their smallness and their motions." 



It would be more correct to refer to p. 149 and to point 



NO. 1640. VOL. 63] 



out that the limits of microscopic vision are defined by 

 the wave-length of light. 



On pp. 48-49, speaking of different kinds of motion, we 

 are told : 



" For instance, a compound of a free path motion 

 with a vibratory motion will give a wave or sinuous 

 motion if the direction of vibration be at right angles to 

 the free path." 



A little further down, on p. 49, the author says : 



" Indeed, we know that some sorts of motion are pro- 

 pagated in the ether. For instance, what we call light 

 is an example. Its form is undid at ory ; and as we have 

 seen an undulatory motion is a compound of a re ctilinear 

 and a vibratory. . . ." 



While seven lines lower down he says : 



" I am not aware that any simple rectilinear motion is 

 known to occur in the ether ; there may be, and likely 

 enough is, such." 



In speaking of non-Euclidean geometry, he suggests a 

 rather curious idea of the relations between men of 

 science of different countries : 



"This new geometry I have alluded to has been 

 worked at by the best mathematicians of all civilised 

 nations, and they agree m their conclusions. They cer- 

 tainly would not do so if there were the slightest appa- 

 rent reason for rejecting them ; for national jealousies 

 are too strong, and a sense of the value of truth too 

 great, to allow any such notions to gain currency any- 

 where if there were any possibilities of breaking them 

 down." 



Here is how the author defines mass, on p. 61 : 



"It has become necessary to find some measure for 

 matter that shall be independent of position, and this 

 has been found by dividing the weight of a body at a 

 given place by the value of gravity at that place and 

 calling the quotient the mass, so that if w represents 

 the weight of the body at a given place and g the value 

 of gravity at the same place, that is the velocity per 

 second that gravity will give to a body if left free to fall, 

 then wig = tn, the mass." 



This definition is calculated to make any reader think 

 that the mass of a body weighing i lb. is 1/32-091 at the 

 equator and 1/32-255 at the poles. How is such an 

 inference to be reconciled with the statement that it is 

 " independent of position " ? 



Further on (p. 346) we have another definition of 

 mass : 



" Mass as a property of matter is generally defined as 

 the amount of matter considered, and is measured by 

 what is called acceleration, that is, the velocity it 

 acquires in a second when acted on by a con stant force 

 or push." 



On p. 106 we have the following definition of tem- 

 perature : 



"The word 'temperature' is used to denote the 

 degree of heat there may be in a unit volume of the 

 substance. . . ." 



According to this, calorimetry would be made easy, 

 for {eg.) a cubic foot of lead and a cubic foot of air at the 

 same temperature should contain the same "• degree of 

 heat "1 As a final sample, we quote the author's explana- 

 tion of the heating of a gas by compression on p. 322 : 



" When a gas is condensed by pressure the individual 

 molecules have less free space to move in, and they con- 

 sequently collide with each other more frequently. Being 



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