Kinetic Theories of Gravitation/Seguin, 1848

Marc Seguin, a French engineer, distinguished as having affirmed in 1839, from a study of the locomotive-engine, the correlation between heat and " work," and as having estimated the " mechanical equivalent " of heat, labored for many years to establish the unity of the natural forces. It is interesting to observe that like Herapath, he commenced his studies in molecular physics with an inquiry into the nature of heat ; and like him, was led to discard entirely the generally-received theory of a material caloric in favor of the kinetic hypothesis now universally adopted.

Nearly a quarter of a century before publishing his views on molecular forces generally, Seguin presented to Sir John Herschel a very original and suggestive communication on the probable nature of heat, which was published by the latter in the Philosophical Journal of Edinburgh for 1824. The writer infers from the compressibility of all known substances that their constituent molecules must be at a great relative distance from each other ; and from the characteristic odor of most solids, that the densest and hardest substances are subject to the escape ot their surface molecules, or in other words, " are capable of being evaporated." From the infinitesimal size of these escaping molecules, they of course elude all known methods of comparison or mechanical appreciation.

"In order to assign to them the condition either of a solid, a liquid, or a gas, it is necessary to suppose the existence and the combination of two forces which are sometimes in equilibrio, and sometimes predominate the one over the other. We shall admit then the supposition that these two forces may be the same as those which regulate the planetary system, and that the molecules of bodies are subject to circulate round one another, so that each body, though it appears at rest, has really a certain quantity of motion, whose measure will be a function of the mass and the velocity of the molecules in motion. Upon these suppositions it is obvious that during the impact of two bodies^ all the quantity of motion which is not employed in giving the body which is struck a motion of translation, will go to augment the quantity of interior motion which it possesses ; and if this motion lakes place in circles or ellipses, the parts will recede from the center of attraction, and the body will increase in volume. In this state it will have a tendency to transmit the excess of motion which it possesses to bodies which are near it, or to parts which it will emit in greater number in following the same law. If the quantity of motion is so great that the attraction of the molecules can no longer be in equilibrio with their angular velocities, the body will remain in the gaseous state till it has transmitted to other bodies, the excess of velocity which it possesses."

This is a very neat and perspicuous presentation of the dynamical [238] theory of temperature, expansion, conduction, evaporation, and the transformation and conservation of energy ; and although three years later than Herapath's remarkable announcement of the theory of gaseous temperature, is doubtless an independent and original discovery ; for such it is entitled to be called. There is now little question that while the molecular excursions in gases take place in straight lines or in hyperbolic trajectories, the atomic motions within the molecule (whose marvelous regularity of periodicity is attested by the fixed refrangibilities of the spectrum) are really described in elliptic orbits, as Seguin had so early preconceived.

The writer proceeds to apply this hypothesis to a variety of apparently unconnected phenomena, as to the sudden development of motion in the fracture of a "Prince Rupert's Drop" or unannealed glass tear; to the action of the steam-engine, in which a large amount of molecular orbital motion in the vaporized water is transformed into the rectilinear or translatory motion of the piston; for "if, as we suppose, an angular motion has been changed into a rectilineal motion or into a motion of trans lation, we should find after the effect only the quantity of motion which has not been employed in producing the useful effect." He shows that the same theory exi)lains satisfactorily the great degree of refrigeration observed in the higher regions of our atmosphere, while by the material theory of caloric the upper regions should be the hottest ; and he maintains that even " the motion produced by organized bodies may be explained in the same manner as the steam-engine." This is certainly a very remarkable prevision of the correlation between the physical and the organic forces.

It was not till 1848 that Seguin commenced a series of memoirs, read before the French Academy of Sciences, on the nature of the molecular forces, but dealing mainly with cohesion regarded as a phase of gravitative action. A theory of mutual impacts and reactions between the molecules of matter and the atoms of the aether was proposed but not very clearly presented. With a communication, made October 22, 1849, the author submitted the results of experiments showing actions "very analogous, if not identical in their effects, with that of gravitation." The apparatus exhibited consisted essentially of a magnet attached to a pendulum which produced motion in small iron bullets suspended a short distance therefrom.

In an editorial resume of Seguin's wonk on "Molecular Physics," in Abbe Moigno's Cosmos, in 1852, the Abbe, after alluding to Newton's speculations, affirms with characteristic confidence and earnestness : " If there is anything certain in the world, it is that the molecules of bodies and bodies themselves are not really self-attractive; it is that attraction is not an intrinsic but only a developed force ; it is that [239] notwithstanding everything occurs as though bodies mutually attracted each other, it is incontestably true that bodies do not so attract. Newton, as Euler, — as every philosopher worthy of the same, — has seen in nature but two things, inertia, and motion originally impressed by a free Will, the first and infinite Mover. And it is with these two great facts of inertia and movement that advancing science shall ultimately explain all the phenomena of the physical world. Already courageous thinkers have endeavored to explain by inertia and motion the great, the capital fact of universal attraction, but these explanations are neither so distinctly formulated nor so plausible as to enable us to give a correct idea of them." Abbe Moigno, as Seguin's interpreter, proceeds ; "The secret of cohesion has been pursued by one of our most illustrious compatriots, M. Seguin, senior, for the last twenty years, and be has certainly discovered it. It consists most essentially, as we shall proceed to show, in the incontestable fact that the molecules of bodies exceed iu number and minuteness anything that could have been imagined."

This theory of cohesion is then set forth at some length, the fundamental assumption being that there are two classes of dynamic monads occupying the universe, the one in a state of relative repose, exhibiting the various phenomena of attraction, and commonly called the ponderable elements, and the other class entirely free or independent, (improperly called imponderable elements,) actuated with extreme velocities of translation, of rotation, and of vibration, continually traversing the systems of ponderable monads in all directions.

Although the admiring editor avows himself a pupil of Seguin, it is doubtful whether he has cautiously followed him, in so enthusiastically proclaiming his development of " a vast theory from the admission of but a single principle in the universe, — the attraction of two monads in the inverse ratio of the distance squared, without recourse to any hypothetical force of mysterious attractions or of impossible repulsions."

In 1858, Seguin published in the Cosmos a somewhat elaborate essay " On the Origin and Propagation of Force," in which he seems to have abandoned a kinetic theory of gravitation. It is true that he there holds : " Matter is inert ; that is to say, it does not harbor in itself the power to put itself into movement, and still less a fortiori to communicate it, since a thing to be transmitted must first exist." And it is also true that he repeatedly speaks of " the great principle of the indefinite conservation of motion " as being " the foundation of all mechanics ;" and regards "the possibility of the destruction of motion as equivalent to " the annihilation of force," which is the very shibboleth of kinetic theorists ; and further that he disputes Poisson's proposition that two spheres of equal mass and velocity, devoid of elasticity, if [240] directly meeting, would have their motion destroyed, and be reduced to rest ; maintaining that " the idea of the possibility of the destruction of force and of the complete disappearance of motion has always been insuperably repugnant to sound and careful thinkers, who have made this question a subject of study."

Notwithstanding all which, he says, in regard to the uniform tendency of a material system to its center of gravity, " we are thus led to consider attraction as a first cause, emanating directly from the Divine Will in the creation of matter. Doubtless it is not impossible that it may hereafter be discovered that attraction in its turn is only a consequence of a more general law, comprehending in itself more implicitly the means of explaining the effects attributed to attraction. . . . But as these considerations are purely metaphysical, since observation cannot reach beyond the established fact that two confronting bodies gravitate toward each other by virtue of a force to which is given the name of attraction, it appears to me wiser not to advance further to penetrate a mystery which nothing within our knowledge as yet appears able to explain. Let us then consider matter as existing from the beginning uniformly in space, and attraction as an essential property with which it is endowed, by virtue of which the different parts or molecules composing it possess in themselves the power of mutual attraction.'

So explicit a statement would seem quite sufficient to prove that Abbe Moigno has in his zeal transcended the doctrines of the one whom he had effusively recognized as his teacher ; and that whatever may have been the earlier views of Seguin as to the origin of gravitation, he can no longer be numbered with those who conceive it to be " a mode of motion."