220 



NA TURE 



[July 7, 1898 



philosopher, that the theory of gravitation was really 

 contained in the laws of Kepler, to whom therefore, and 

 not to Newton, the discovery of gravitational attraction 

 was due. The utterance was a remarkable one for a 

 philosopher who always contended that the object of 

 philosophy was, as no doubt it is, to find unity in 

 diversity. It only shows that even divine philosophy 

 does not always suffice to lift a man above national 

 iealousy and prejudice. The law of gravitation was the 

 one uniting principle, the unity which explained the 

 whole range of planetary motions, brought into one view 

 the motion of the moon and the fall of a stone, enabled 

 the motions of the heavenly bodies to be computed, 

 and the places of the bodies predicted for a long range 

 of future time, and gave the keynote for those great in- 

 vestigations of the future and the past of the solar 

 system, and of our own terrestrial system within it, 

 which have been carried out since Newton's time by 

 his followers. Some of the greatest of these researches 

 — we may well be proud of the fact— have been carried 

 out by scientific men of our own country, whom this age 

 has either seen or still possesses. 



Like Maxwell's electrical theory the Newtonian gravi- 

 tation raised, as does every really science-making theory, 

 questions which it did not answer. There is the further 

 problem of the rationale and mechanism of gravitationj 

 and questions of its application to close aggregates of 

 particles, and our minds are suddenly turned from the 

 stars in their courses to the structure of molecules and 

 the nature of inter-molecular action. The new problems 

 bristle with difficulties far greater than those which have 

 been surmounted, the new standing ground attained has 

 only disclosed steeper heights to be scaled. 



So it has been in the electromagnetic theory of light. 

 The conception of a plane wave of light as a propagation 

 of a disturbance in which there is electric, and at the 

 sarhe time magnetic, intensity varying as a simple har- 

 monic function of the time, and its minute verification by 

 Hertz and his pupils, and by others, has opened whole 

 vistas of problems we cannot hope to solve for many a 

 day. There are the primary questions, whether the 

 theory of the ether, according to which light vibrations 

 are transmitted as waves of distortion in a medium for 

 which the ratio of the rigidity modulus to the density is 

 enormous, has any foundation in fact, and, if so, what is 

 the relation of the varying electric and magnetic forces to 

 the material vibrations ; how do these electric and mag- 

 netic forces arise, and how are they maintained in the 

 ether : in short, how does matter act upon ether and ether 

 uopn matter. In these are involved others of perhaps a 

 more limited or special nature, the mode of localisation 

 of energy in fields in a steady state, and the mode of flow 

 of energy in cases of transference. The complete solu- 

 tion of these would yield the secret of voltaic action, and, 

 it might be, reduce the voltaic cell to a magneto-electric 

 machine, and tell us in what magnetic and electric 

 induction themselves consist. 



That Mr. Glazebrook's book can be of great interest, 

 even to those who are more or less familiar with Camp- 

 bell and Garnett's life of Maxwell, we can fully testify. 

 It is true that most of the early reminiscences given in 

 the biographical sketch are to be found in the life ; 

 but there are personal recollections of Mr. Glazebrook's, 

 NO. 1497, VOL. 58] 



and several other touches here and there, which give 

 this part of the work a charm and value of its own. 

 This is followed by one or two specimens of the verses 

 which Maxwell from time to time threw off, sometimes in 

 a serious mood, sometimes in a gay, but always with a 

 grace of expression and originality (and at times a quirki- 

 ness amounting almost to caprice) of thought peculiarly 

 his own. The specimens chosen are the inimitable 

 parody in verse of Tyndall's Belfast Address, the verses 

 on " Molecular Evolution," written on the same occasion, 

 the verses addressed "To the Committee of the Cayley 

 Portrait Fund," and the song of the Rigid Body. A it.vf 

 more might have been included without giving too much 

 illustration of this side of Maxwell's versatile nature. 

 The rapidity and ingenuity of his verse composition were 

 extraordinary. The writer well remembers seeing on a 

 sheet of the article " Elasticity," written by Lord Kelvin 

 for the ninth edition of the " Encyclopaedia Britannica," a 

 copy of verses which Maxwell had jotted down before 

 returning the proof. It began : 



' ' Vex not my ears, ye crystal spheres, 

 Your harmony's insipid, O. 

 But play again that tuneful strain, 

 My parallelepiped, O." 

 And so on, 



" Finding great fun in twenty-one 

 Elastic moduluses, O ! " 



for six or eight verses, with marvellous rhymes for 

 the numerous, and for purposes of verse somewhat in- 

 tractable, technical terms with which a mathematical 

 discussion of the elasticity of an aeolotropic solid 

 abounds. 



His letters also were very beautiful, and serve as a 

 comforting reminder that if letter-writing is a lost art, it 

 survives still in some men of playful fancy and lightness 

 of touch as a natural gift. Of these only a i^^N speci- 

 mens are given by Mr. Glazebrook, and hardly more 

 could have been included within the limits of space at 

 his disposal. 



The rest of the book consists of a sketch of Maxwell's 

 work in Colour Vision, Molecular Theory of Gases, and 

 Electricity. This we need not review. Suffice it to say 

 that it is thoroughly clear and trustworthy, and will well 

 repay perusal by the physicist already acquainted with 

 later developments of Maxwell's work. Mr, Glazebrook 

 has also found room for a valuable concluding sketch of 

 the work of Hertz and his followers, which was founded 

 on Maxwell's theory, and afforded its experimental 

 verification. 



There are one or two misprints. .At p. 68, the Don 

 referred to oddly enough turns a watch; and there is 

 another, near the beginning of the foot-note on p. 131. 

 The biographical reference to George Green, of Notting- 

 ham, on p. 158, is not quite accurate.^ 



1 It is strange that the ninth edition of the " Encyclopaedia Britannica" 

 should contain no biography of Green. He was undoubtedly a great genius, 

 and made an impression, not merely on mathematical physics, but on pure 

 analysis, which will never be effaced. It has been said in jest, but with 

 considerable truth, that applied mathematics is made up of continual 

 applications of Green's theorem. Of this enormously powerful theorem a 

 more lately discovered relation, which is very fundamental in the theory of 

 functions of a complex variable, and which is generally quoted as Riemann's 

 theorem, is only a particular case. 



Green's career was certainly very remarkable : but Mr. Glazebrook is in 

 error as to his original occupation. Up to the year 1829 he assisted 

 his father, who was in business first as a baker in Nottingham, and after- 

 wards as a miller in the neighbouring village of Sneinton. In that year, wher> 

 Green was thirty-six years of age, his father died, and not long after Green 



