Principles of Energetics. 353 
the object of the latter “is to clear the way for speculation *,” 
rather than to advance a complete general theory. 
In examining Professor Challis’s ‘ fundamental hypothetical 
facts,” I hope to show that they are opposed (1) by Newton’s 
Rules of Philosophizing; (2) by the principles of Metaphysics, 
as the modern Science of the Conditions of Thought; and (3) by 
the conceptions of matter, of the interaction of its different parts, 
and of motion and force, to which modern experimental researches 
have led. 
21. “The fundamental hypothetical facts on which the [Prof. 
Challis’s| theory rests are, that all substances consist of minute 
spherical atoms, of different, but constant, magnitudes, and of the 
same intrinsic inertia, and that the dynamical relations and 
movements of different substances are determined by the mo- 
tions and pressures of a uniform elastic medium pervading: all 
space not occupied by atoms, and varying in pressure in propor- 
tion to variations of its density+.” Prof. Challis further says 
that he has “been guided by Newton’s views on the ultimate 
properties of matter, especially as embodied in the Regula Tertia 
Philosophandi in the Third Book of the ‘ Principia’; ” and that 
he has merely “‘ added to the Newtonian hypotheses two others, 
viz. that the ultimate atoms of bodies are spherical, and that they 
are acted upon by the pressure of a highly elastic medium ft.” 
But on reference to the cited rule, no “ Newtonian hypotheses” 
will be found, only a statement of the.actual general qualities of 
matter. And, setting aside the “additional hypothesis” of 
sphericity, so far are the hypotheses of ultimate indivisible 
atoms, and these of an indeterminate number of different sizes, 
though of the same intrinsic inertia, Newtonian, that Newton 
says, ‘At si vel unico constaret experimento quod particula 
aliqua indivisa, frangendo corpus durum et solidum, divisionem 
pateretur; concluderemus vi hujus regule, quod non solum 
partes divisee separabiles essent, sed etiam quod indivise in infi- 
nitum dividi possent.”” And Le Seur and Jacquier add in their 
note: “Hine patet differentia Newtonianismi et hypotheseos 
Atomorum; Atomiste necessario et metaphysicé atomos esse 
indivisibiles volunt, ut sint corporum unitates ; Metaphysicam 
hane queestionem missam facit Newtonus . . . . omnem hace de re 
Theoriam Metaphysicam experimentis facile postponens.” So 
that not only are Professor Challis’s hypotheses as to “ ulti- 
mate” bodies unwarranted by the rule he vouches, but he 
appears as of that very metaphysical school of Atomists, New- 
* «The Theory of Molecular Vortices applied to Magnetic Phenomena,” 
Phil. Mag. March, p. 162. 
+ Phil. Mag. Feb. 1861, p. 106. t Ibid. Dec. 1859, pp, 443 and 444, 
Phil. Mag, 8. 4. Vol. 21. No. 141, May 1861. 2A 
