1^6 



NA TURE 



[December 7, 1893 



divided the prize between Cartesians and Newtonians. Thus, 

 in 1734, the question being the cause of the inclination of the 

 orbits of the planets, the prize was shared between John Ber- 

 noulli, whose memoir was founded on the system of vortices, 

 and his son Daniel, who was a Newtonian. The last act of 

 homage of this kind to the Cartesian system was performed in 

 1740, when the prize on the question of the tides was distributed 

 between Daniel Bernoulli, Euler, Maclaurin, and Cavallieri ; 

 liic last of whom had tried to amend and patch up the Cartesian 

 hjrpothesis on this subject.^ 



On February 4, 1 744, Daniel Bernoulli wrote as follows to 

 Euler : " Uebrigens glaube ich, dass der Aether sowohi gravis 

 versus solem, als die Luft versus terram sey, und kann Ihnen 

 night bergen, dass ich iiber diese Puncte ein volliger New- 

 tonianei bin, vnd verwundere ich mich, dass sie den Principiis 

 Cartesianis so lang adhariren ; es mochte wohl einige Passion 

 vielleicht mit unterlaufen. Hat Gott konnen eine animam, 

 deren Natur uns unbegreiflich ist, erchaffen, so hat er auch 

 konnen eine attractionem universalem materiae imprimiren, wen 

 gleich solche attractio JM/ra fa//?</« ist, da hingegen die Prin- 

 cipia Cartesiana allzeit contra captwn etwas involviren." 



Here the writer, expressing wonder that Euler had so long 

 adhered to the Cartesian principles, declares himself a thorough- 

 going Newtonian, not merely in respect to gravitation versus vor- 

 tices, but in believing that matter may have been created simply 

 with the law of universal attraction without the aid of any gra- 

 vific medium or mechanism. But in this he was more New- 

 tonian than Newton himself. 



Indeed .Newton was not a Newtonian, according to Daniel 

 Bernoulli's idea of Newtonianism, for in his letter to Bentley to 

 date February 25, 1792,- he wrote: "That gravity should be 

 innate, inherent, and essential to matter, so that one body may 

 act upon another at a distance through a vacuum without the 

 mediation of anything else, by and through which their action 

 and force may be conveyed from one to another, is to me so 

 great an absurdity that I believe no man who has in philoso- 

 phical matters a competent faculty of thinking can ever fall 

 into it." Thus Newton, in giving out his great law, did not 

 abandon the idea that matter cannot act where it is not. In 

 respect, however, of merely philosophic thought, we must feel 

 that Daniel Bernoulli was right ; we can conceive the sun at- 

 tracting Jupiter, and Jupiter attracting the sun, without any 

 intermediate medium, if they are ordered to do so. But the 

 question remains. Are they so ordered ? Nevertheless, I believe 

 all, or nearly all, his scientific contemporaries agreed with 

 Daniel Bernoulli in answering this question affirmatively. Very 

 soon after the middle of the eighteenth century Father F.osco- 

 vich ^ gave his brilliant doctrine (if infinitely improbable theory) 

 that elastic rigidity of solids, the elasticity of compressible liquids 

 and gases, the attractions of chemical affinity and cohesion, the 

 forces of electricity and magnetism — in short, all the properties 

 of matter except heat, which he attributed to a sulphurous fer- 

 menting essence — are to be explained by mutual attractions and 

 repulsion^, varying solely with distances, between mathematical 

 points endowed also, each of them, with inertia. Before the 

 end of the eighteenth century the idea of action-at-a-distance 

 through absolute vacuum had become so firmly established, and 

 Boscovichs theory so unqualifiedly accepted as a reality, that 

 the idea of gravitational force or electric force or magnetic force 

 being propagated through and by a medium seemed as wild to 

 the naturalists and mathematicians of 100 years ago as action-at- 

 a-distance had seemed to Newton and his contemporaries lOO 

 years earlier. But a retrogression from the eighteenth century 

 school of science set in early in the nineteenth century. 



Faraday, with his curved lines of electric force, and his di- 

 electric efficiency of air and of liquid and solid insulators, re- 

 suscitated the idea of a medium through which, and not only 

 through which but by which, forces of attraction or repulsion, 

 seemingly acting at a distance, are transmitted. The long 

 struggle of the first half of the eighteenth century was not merely 

 on the question of a medium to serve forgravific mechanism, but 

 on the correctness of the Newtonian law of gravitation as a 

 matter of fact however explained. The corresponding con- 

 troversy in the nineteenth century was very short, and ic soon 

 became obvious that Faraday's idea of the transmission of electric 



1 Whewell's " History of the Inductive Sciences," vol. ii. pp 198, 199. 



- " The Correspondence of Richard Bentley, B. L).'' vol. i. p 70. 



3 " Theoria Philosophiae Naluralis redacta ad unicam legem virium in 

 natura existentium auctore P. Rogerio Josepho Boscovich, Societatis Jesu," 

 1st edition, Vienna, 1758 ; 2nd edition, amended and extended by the author, 

 Venice. 1763. 



force by a medium not only did not violate Coulomb's law of 

 relation between force and distance, but that, if real, it must 

 give a thorough explanation of that law.^ Nevertheless, after 

 Faraday's discovery - of the different specific inductive capaci- 

 ties of different insulators, twenty years passed before it was 

 generally accepted in continental Europe. But before his 

 death, in 1867, he had succeeded in inspiring the rising genera- 

 tion of the scientific world with something approaching to faith 

 that electric force is transmitted by a medium called ether, of 

 which, as had been believed by the whole scientific world for 

 forty years, light and radiant heat are transverse vibrations. 

 Faraday himself did not rest with this theory for electricity 

 alone. The very last time I saw him at work in the Royal 

 Institution was in an underground cellar, which he had chosen 

 for freedom from disturbance ; and he was arranging experi- 

 ments to test the time of propagation of magnetic force from an 

 induction coil through a distance of many yards to a fine steel 

 needle polished to reflect light ; but no result came from those 

 experiments. About the same time, or soon after, certainly not 

 long before the end of his working time, he was engaged (I 

 believe at the shot tower near Waterloo Bridge on the Surrey 

 side) in efforts to discover relations between gravity and mag- 

 netism, which also led to no result. 



Absolutely nothing has hitherto been done for gravity either 

 by experiment or observation towards deciding between Newton 

 and Bernoulli as to the question of its propagation through a 

 medium, and up to the present time we have no light, even so 

 much as to point a way for investigation, in that direction. But 

 for electricity and magnetism, Faraday's anticipations and Clerk- 

 Maxwell's splendidly developed theory have been established on 

 the sure basis of experiment by Hertz's work, of which his own 

 most interesting account is this year presented to the world in 

 the German and English volumes to which I have referred. It 

 is interesting to know, as Hertz explains in his introduction, 

 and it is very important in respect to the experimental demon- 

 stration of magnetic waves to which he was led, that he began 

 his electric researches in a problem happily put before him thir- 

 teen years ago by Prof, von Helmholtz, of which the object was 

 to find by experiment some relation between electromagnetic 

 forces and dielectric polarisation of insulators, without, in the 

 first place, any idea of discovering a progressive propagation of 

 those forces through space. 



It was by sheer perseverance in philosophical experimenting 

 that Hertz was led to discover a finite velocity of propagation 

 of electromagnetic action, and then to pass on to electro- 

 magnetic waves in air and their reflection, and to be able to say, 

 as he says in a short reviewing sentence at the end of his eighth 

 paper : " Certainly it is a fascinating idea that the processes in 

 air which we have been investigating, represent to us on a 

 million-fold larger scale the same processes which go on in the 

 neighbourhood of a Fresnel mirror, or between the glass plates 

 used for exhibiting Newton's rings." 



Prof. Oliver Lodge has done well in connection with Hertz's 

 work, to call attention -^ to old experiments, and ideas taken from 

 them, by Joseph Henry, which came more nearly to an experi- 

 mental demonstration of electromagnetic waves than anything 

 that had been done previously. Indeed, Henry, after describing 

 experiments showing powerful enough induction due to a single 

 spark from the prime conductor of an electric machine to mag- 

 netise steel needles at a distance of thirty feet in a cellar beneath 

 with two floors and ceilings intervening, says that he is " dis- 

 posed to adopt the hypothesis of an electrical plenum," and 

 concludes with a short reviewing sentence : " It may be further 

 inferred that the diff"usion of motion in this case is almost com- 

 parable with that of a spark from a flint and steel in the case of 

 light." 



Prof. Oliver Lodge himself did admirable work in his investi- 

 gations with reference to lightning rods,'* coming very near to 

 experimental demonstrations of electromagnetic waves ; and he 

 drew important lessons regarding " electrical surgings " in an 

 insulated bar of metal "induced by Maxwell's and Heaviside's 

 electromagnetic waves," and many other corresp>onding pheno- 

 mena manifested both in ingenious and excellent experiments 

 devised by himself and in natural effects of lightning. 



Of electrical surgings or waves in a short msulated wire, and 



^ " Electrostatics and Magnetism," Sir W. Thomson, Arts. I. (1842) and 

 II. (1845), particularly § 25 of Art. II. 



- 1837, "Experimental Researches," 1161-1306. 



•> " Modern Views of Electricity," pp. 369-372. 



■* "Lightning Conductors and Lightning Guards," Oliver J. Lodge. 

 F.R.S. Whittaker and Co. 



NO. 1258. VOL. 49] 



