6o4 



NA rURE 



[April 27, 1893 



determine that on the whole no energy shall flow from 

 one to the other when placed in contact or radiating to 

 one another. 



There are many other matters treated of in the book, 

 but if one were to take " Waterdale " at his word and 

 judge " whether the rest of the book is worthy or not of 

 careful perusal" by one's experience of Appendix II. and 

 its supposed proof, nobody would read another word, and 

 unless one had a great deal of leisure to devote to specu- 

 lative conjectures, or were well paid for it, there does not 

 seem much inducement to wade very carefully through 

 it. " Waterdale " professes to e.xplain gravitation by a 

 sort of hotch-potch of Bjerknes' sound wave attractions 

 and Osborne Reynolds's theory founded on dilatancy. 

 He seems to think that any attempt to explain gravi- 

 tation is very remarkable. " The author would have 

 thought that when the unusual occurrence of the publi- 

 cation of a work announcing the discovery of gravity 

 and other original theories as important arises, that the 

 scientific world would display sufficient interest in the 

 subject as to read and examine the arguments, although 

 the work might be by an unknown pen." " " Wateriale " 

 seems ignorant of the fact that the scientific world has 

 been inundated with theories of gravity and other original 

 theories. To mention only a few of the better known 

 ones, there are Le Sage's corpuscular theory, worked out 

 very carefully by Mr. Tolver Preston and Mr. George 

 Forbes, Others founded on wave motion and fluid flow, 

 such as Bjerknes has popularized, and which Mr. Karl 

 Pearson has devoted so much ingenuity to, though he 

 takes refuge in nondynamical suggestions, such as a 

 fourth dimension, which might just as well be introduced 

 as a region in which a convenient series of strings existed 

 to hold atoms together without any action at all going on 

 in our stupid tridimensional space. What the difference 

 is between such a theory and the good old hypothesis of 

 inherent qualities seems difficult to discover. Then there 

 is the suggestion that every atom is connected to every 

 other by means of vortex filaments, though how the poor 

 things work when they get tangled is rather a difficulty 

 nere. Finally, there is Osborne Reynolds's interesting 

 theory founded on dilatancy, which very possibly has a 

 future before it, especially if we consider that the ether 

 is probably full of vortices, and that vortices cannot cut 

 one another. These theories almost all suffer from the 

 apparently incurable defect to which " Waterdale's" is also 

 liable, that they give a rate of propagation of gravity 

 comparable with that of light. Parents are proverbially 

 partial to their children, and " Waterdale " probably will 

 cherish his suggestions as very valuable, notwithstanding 

 this and other serious objections. The confident way in 

 which, after pages of suggestions as to what might happen, 

 he staies that a current from right to left will produce one 

 eff'ect, while one from left to right will not neutralise it is 

 quite refreshing, but is not an attractive investigation to 

 those who are accustomed to call nothing a proof that is 

 not founded upon something better than suggestions. 

 That gravity is propagated with such amazing rapidity 

 as it is seems to show that it must be an action of 

 the medium to whose structure the electromagnetic 

 properties of the ether are due. Such actions are known 

 to exist in a perfect liquid, and it is natural to attribute 

 gravity to such actions. The reasons for attributing great 

 NO. I 226, VOL. 47] 



velocity of propagation to gravity are not apparently 

 very well known. The difficulty is owing to the com- 

 ponent of the force at right angles to the radius vector 

 that would come in, owing to the aberration of the force,, 

 and which would cause an acceleration of areas of planets. 

 This might be partly neutralized by a resisting medium, 

 but hardly completely, especially in the case of comets, 

 because the resisting force would be tangential to the 

 path, while the aberration component would be at right 

 angles to the radius vector. It is possible, by assuming 

 an increase of force due to velocity of approach and a 

 decrease due to recession, to get over this latter difficulty ; 

 but even then it is hard to explain the persistent rotation 

 of the earth when the surface is not moving freely as a 

 projectile, and when consequently the supposed exact 

 balance between gravitational acceleration and resistance 

 of medium does not hold. Even then there is the pos- 

 sible suggestion that cohesional and other forces, being 

 similarly propagated in time, would prevent any possible 

 eff'ect being produced by the resisting medium, and so 

 matters return to much as they were at first, and no 

 final answer be given to the questions, " Is gravity pro- 

 pagated in time ?" " Does the ether off"er resistance to 

 motion ?" It remains much in the same position as the 

 question of the motion of the ether at the surface of the 

 earth. 



" Waterdale " and others seem to think that fluidity 

 necessarily implies that a medium is divisible into hard 

 or soft particles. No ordinary mind is forced to this 

 conclusion. Most minds look upon water, for instance,, 

 as a perfectly continuous medium, any part of which can 

 flow past any other part with perfect freedom. Hard- 

 ness, softness, and so forth may require structure, but 

 mere fluidity does not. Again, " Waterdale " and others 

 seem to imagine that elasticity essentially involves the 

 compressibility of the elastic body : i.e. that it must 

 consist of atoms that are themselves compressible. 

 "Waterdale" himself invents a structure for an atom 

 that resists deformation without its constituents being 

 themselves compressible, and the existence of voitex 

 rings shows how a perfect liquid can have a real elas- 

 ticity to deformation given to a part of it by giving it 

 motion without any part being composed of particles, or 

 any part of it being at all compressible. 



The rest of " Waterdale's Researches" concern sug- 

 gestions as to how cohesion, chemical action, light, 

 electricity, &c., may at some future time be explicable by 

 the structure he proposes for the ether, which is to 

 all intents and purposes the same as Osborne Reynolds 

 already has suggested, a whole collection of absolutely 

 hard bodies of different sizes, or, as " Waterdale " sug- 

 gests, spheres of two different sizes. There is consider- 

 able cleverness displayed in the way he has reasoned out 

 for himself such a well-known theorem as that a body 

 moving in a perfect liquid will behave as if its mass 

 were increased, but the labour bestowed upon such a 

 well-known theorem does not entice the reader to try 

 and follow the vague suggestions that follow, and that 

 are much the same as have been over and over again 

 given to show how every theory as to the nature of the 

 ether explains a lot of things which can on ths face of 

 them be explained by any ether through which bodies 

 can move, and upon which they exert pressures. Mixed 



