1 44 Reflection and Refraction of Light. 



as mere hypotheses ? I have therefore discarded them, and admit that 

 alone which we know lias a veal and actual existence, namely, gravitation. 

 Some are startled at this, but if it be found sufficient, why encumber the 

 subject with obstacles, weights, and barriers ? Guided then by the in- 

 fluence of correct analysis, we seize this principle, and follow it upward to 

 the celestial regions, and downwards to the centres of atoms j the legitimate 

 and only true rules of philosophizing do not allow us to stop in either 

 direction, while any space is left unexplored. This force, whose effects have 

 guided our inquiries, we find reversed in the immediate vicinity of the 

 centre; this may be called repulsion, because of its opposite direction, but 

 still it is the same force as that of the attraction, being of the same nature, 

 and regulated by the same laws. Hence nature herself leads us by the 

 hand of genuine philosophy to a just notion of matter : and places before 

 us this demand, this postulate, that an atom of matter consists of a system 

 of force, varying inversely as the square of the distance, acting a little 

 way outwardly, or from the centre, and thus forming a sphere of repulsion, 

 but towards the centre, at all greater distances, forming a sphere of at- 

 traction. Again, there is nothing to prevent a difference in the absolute 

 forces of different atoms, or in the radii of their spheres of repulsion, and 

 phaenomena requite these differences j hence nature makes a second demand, 

 viz. that the atoms of matter differ in these respects : and this difference 

 is sufficient to account for tiie many sorts of matter which come under our 

 review, or indeed ten thousand times greater varieties. 



9. Thus, for example, an atom of oxygen has a given absolute force, and 

 radius of its sphere of repulsion ; the same may be said of hydrogen ; but 

 phaenomena indicate that the force of the oxygen is about sixteen times 

 greater than that of hydrogen, while its sphere of repulsion is less. Simi- 

 larly every different sort of atom has its own peculiar force and sphere of 

 repulsion. In every system we must admit that the materials are duly 

 apportioned ; all tilings are produced according to number, weigiit, and 

 measure. Now nature points out at least two grand classes of atoms, dis- 

 tinguished by a very great differeuce in their absolute forces : those which 

 form solid bodies I call tenacious atoms, because we find them adhering with 

 great tenacity, — they constitute common matter ; atoms of the other class 

 are called ethereal, because as we observe them, they form collections, or 

 bodies, such as are denominated ethereal fluids. 



10. It is manifest that one of the former, being present in a mass of the 

 latter, will attach to its surface of repulsion a vast number of them, closely 

 crowded together : for, to conceive rightly of this, assume the absolute force 

 of oxygen to be three hundred and twenty million times greater than that of 

 an ethereal atom. It is manifest that the oxygen would draw to its surface 

 the centres of the ethereal atoms, till the force between them become nearly 

 equal to that of the oxygen at the same surface ; hence the distance between 

 the centres would be about the T^^^g^^^ part of the radius of the sphere of 



