154 SCIENCE PROGRESS 



In a lecture delivered in Edinburgh, a short account of which commences this 

 volume, he remarks : " Lucretius' atom does not explain any of the properties 

 of matter without attributing them to the atom itself. It is as easy (and as im- 

 probable—not more so) to assume whatever forces may be required in any 

 portion of matter which possesses the (Wirbelbewegung) as in a solid indivisible 

 piece of matter." 



The extraordinary skill displayed in finding the solutions of given mathe- 

 matical problems is only surpassed by the insight, clearness of thought and 

 power to translate physical phenomena into mathematical language shown 

 in these pages. The reader feels that here he is dwelling with one who is on 

 the verge of wresting from Nature some of her hidden secrets ; but alas ! with 

 all the wonderful insight and mathematical skill, the theory could not yield a satis- 

 factory explanation, to use Thomson's own words "of universal gravitation or 

 any other property of matter"; and even less could he see hope of it "explaining 

 chemistry and electro- magnetism." The quest was a grand one and he pursued 

 it unflinchingly, even though he had to admit, ten years after the time of writing 

 the last of the papers on Vortex Motion given in this volume, that it was to the 

 end— failure. 



The second part of the book consists of three papers on the " Theory of the 

 Tides," the first being the famous paper " On an alleged error in Laplace's 

 Theory of the Tides," in which he defends Laplace against Airy and Ferrel, 

 showing that the procedure of Laplace was correct ; with rare skill in this and the 

 following two papers he developes and improves the beautiful theory of the famous 

 French mathematician. 



The third part is closely allied with the second, consisting of eleven papers on 

 " Waves on Water," a subject, as also that of tides, to which the author, from a 

 practical and theoretical standpoint, the former not being dealt with in this volume, 

 made such notable contributions. The last paper in this section is a short note on 

 the " Physical Explanation of the Mackerel Sky." All that is essential to the forma- 

 tion of a mackerel sky " is that portions of air should be moving up and down ; and 

 further, that the up-and-down motion should seem as though it resulted from the 

 slipping of one stratum of air upon another and the production thereby of waves ; 

 and the second essential is that one or other of the two portions of air should be 

 very near the point of saturation — that it would be clear when down at its lowest 

 point and cloudy when up at its highest." Space forbids many remarks on the 

 papers on Waves, but in the one on "Deep-Water Ship-Waves," written ten years 

 after the last of the papers on " Vortex Motion," he admits that the motion in the 

 Helmholtz circular ring is unstable, and if the water in the whirlpools formed by a 

 ship " suddenly loses viscosity and becomes a perfect fluid, the dynamics of vortex 

 motion tells us that the rotationally moving water gets left behind by the ship, and 

 spreads out in the more distant wake and becomes lost ; without losing its kinetic 

 energy, which becomes reduced to infinitely small velocities in an infinitely 

 large portion of the liquid." The fourth section includes a number of papers on 

 General Dynamics, in some of which one sees how the author was endeavouring 

 to conceive dynamical models to illustrate the properties of matter. He deals with 

 " Elasticity viewed possibly as a mode of motion " and concludes by suggesting that 

 there is yet in store for the world a beautiful work bearing this title. 



In the paper " On the Gyrostatic Working Model of the Magnetic Compass," 

 it is shown how gyrostats suspended in suitable manners can be made to act as a 

 dipping needle and magnetic compass respectively ; and in an abstract from a 

 lecture on Gyrostatic Experiments given at Belfast, he expresses the belief that 



