among other valuable results, that those portions of the fluid which at any time possess rotation preserve it for ever, and are thus as it were marked off from the others; also that these portions must be arranged in filaments whose direction is at each point the axis of rotation, and that the filaments are either endless, i.e. form closed curves (whether knotted or not), or terminate in the free surface of the fluid.

Hence Sir William Thomson's idea that what we call matter may consist of the rotating portions of a perfect fluid, which continuously fills space. This definition involves the necessity of a creative act for the production or destruction of the smallest portion of matter, because rotation can only be produced or destroyed by us in a fluid in virtue of its viscosity (or internal friction), and in a perfect fluid there is nothing of the kind.

134. Of course it may be objected to this theory that it merely shifts the difficulty one step further back,—after all, explaining what we call matter by certain motions of something which, as it must have inertia, it would appear we are bound to call matter also. We have mentioned this (latest) speculation as to the nature of matter for two reasons: 1st, because it shows one way of at once thoroughly accounting for the conservation of tangible matter; 2d, because it shows the possibility of forming an idea of a true atom which shall not require, even for perfect elasticity, the inconceivable quality of perfect hardness necessary to the atom of Lucretius. In fact, the few words which we have given above about Helmholtz's investigations show that, to cut a vortex atom, it would be necessary to give a free surface to the perfect fluid which on this theory is supposed to fill space, i.e. virtually to sever space itself! This

idea promises to be very valuable from one point of view at least, viz., the extension and improvement of mathematical methods; for in its very elements it requires the application of the most powerful of hitherto invented processes, and, even with their aid, the mutual action of two ring-vortices (the simplest possible space-form) has not yet been investigated except in the special cases of symmetrical disposition about an axis. Hence we are at present altogether unable to guess whether this idea will or will not pass with credit some of the most elementary examinations to which a theory of the ultimate nature of matter must of course be subjected.

135. Take them for what they are worth. The four forms of speculation we have just sketched represent the most plausible guesses yet propounded as to the ultimate nature of matter, the second being, probably because the most artificial and the most arbitrary, the most completely developed. For in it the representation is self-contained as it were; it does not base itself upon extraneous postulates, as of ultimate hard particles (of what?), nor upon vortex motion (of what? again), nor, finally, upon mere intense heterogeneity (of what? once more), as do the other three. But we naturally object to it as refining away altogether the idea of stuff or substance which the mind seems to require as something underlying the notion of anything which is found to be directly capable of affecting our senses.

136. The reader who has followed us so far, must now see that our notions of the nature of matter are, at best, but hazy. We know, it is true, a great many of its properties very exactly, so much so indeed, as to be able to deduce from them mathematically an immense variety of con

sequences which subsequent experiment shows to be correct, at least within the limits of accuracy of our methods of observation and measurement. But as to what it is we know no more than Democritus or Lucretius did, though as to what it may be or may not be we are perhaps considerably better prepared with an opinion than they could possibly be.

137. We have seen in the preceding chapter that energy is never found separate from matter, so that we might, with perfect propriety, define matter as the seat or vehicle of energy that which is essential to the existence of the known forms of energy, without which, therefore, there could be no transformations of energy, and therefore no life such as we now know it.

138. Now the transformability of a given amount of energy, or, at least, the modes of its transformation, depend in a very curious manner upon the relative quantity of matter with which it is associated. A pillow or bolster (stuffed with eider-down, let us say) of 30 lbs. weight, and moving at 10 feet per second-i.e. as if it had fallen from a height of considerably less than two feet,-has nearly the same energy as a pellet of No. 1 shot when it leaves the muzzle of a fowling-piece. How different the quality of these equal quantities even of energy of the same kind! Yet, delivered horizontally, the one would correspond to a staggering push which few men could resist if it came unexpectedly; while the other would scarcely affect one's equilibrium, though it might easily kill by penetrating a vital organ. [In the brutal pastimes of the last generation, as we now in our advanced humanitarianism call them, this was well known as the difference between the effects of a slow knock-down' blow by a heavy-weight, and a "punishing facer" from a feather

weight. Alas for the good old times! for our comparison, apt as it is, is too probably thrown away on the degenerate inhabitants of (once) merry England, erewhile the home of the "Miller," with his honest quarterstaff, of jolly and chivalrous wrestlers, boxers, and bowmen, now the hell of running-kicks, garrotting, gouging, and stabbing.

Aetas parentum, pejor avis, tulit

nos nequiores, mox daturos

progeniem vitiosiorem.

The dissipation of energy is a great fact in a moral as well as in a physical sense. In those good old times men fought with men, -irrepressible energy, rather than any sordid passion or uncontrolled vice, constantly pulling the trigger! Now creatures in the likeness of men vent their despicable passions in murderous assaults upon women and children. But science hints at an effectual cure. It is probable that before many years have passed, electricity, which by some mysterious means enables our nerves to call our muscles into play, which enables us to converse with one another at distances of thousands of miles, which alike plates the teaspoon and illumines the lighthouse, will be called upon by an enlightened legislature to produce absolutely indescribable torture (unaccompanied by wound or even bruise), thrilling through every fibre of the frame of such miscreants.]

139. After inertia, which is not accounted for by any of the hypotheses as to the ultimate nature of matter which we have just given, the most general property of matter which we recognise is that of universal gravitation, in virtue of which portions of matter, if situated at a distance from one another, are possessed of potential energy. We are apt to hold exaggerated notions of the immense power of gravity;

but a little consideration will show us that it is in reality one of the most trivial of the forces to which matter is directly or indirectly subject.

Think for a moment of the fundamental experiments in electricity and magnetism, known to men for far more than 2000 years, the lifting of light bodies in general by rubbed amber, and of iron filings by a loadstone. To produce the same effects by gravitation-attraction, at least if the attracting body had the moderate dimensions of a handspecimen of amber or loadstone,—we should require it to be of so dense a material as to weigh at the very least 1,000,000,000 lbs., instead of (as usual) a mere fraction of a pound. Hence it is at once obvious that the imposing nature of the force of gravity, as usually compared with other attractive forces, is due not to its superior qualitative magnitude, but to the enormous masses of the bodies which exercise it.

In fact, the excessively delicate Torsion-balance of Michell was absolutely requisite to demonstrate, much more to measure, the mutual attraction between a large and a small leaden sphere. And (unless the third of the hypotheses as to the nature of matter above given be correct, in which case the form of our statement would require modification) small or even moderately large pieces of matter are held together entirely by cohesion, gravitation being absolutely insensible; though in a huge mass like the earth, the force exerted by one hemisphere on the other (i.e. the force which would be called into play to prevent its being split in two) depends mainly upon gravitation, in comparison with whose enormous amount even a cohesive force of 500 lbs. per square inch over a circular surface of 4000 miles radius sinks into utter insignificance !