It may be said, first: “The proof that the force of irradiation (in the case described) is directly proportional to the squares of the distances, depends upon an unwarranted assumption—that of the number of atoms in each stratum being the measure of the force with which they are emitted.” I reply, not only that I am warranted in such assumption, but that I should be utterly _un_warranted in any other. What I assume is, simply, that an effect is the measure of its cause—that every exercise of the Divine Will will be proportional to that which demands the exertion—that the means of Omnipotence, or of Omniscience, will be exactly adapted to its purposes. Neither can a deficiency nor an excess of cause bring to pass any effect. Had the force which irradiated any stratum to its position, been either more or less than was needed for the purpose—that is to say, not _directly proportional_ to the purpose—then to its position that stratum could not have been irradiated. Had the force which, with a view to general equability of distribution, emitted the proper number of atoms for each stratum, been not _directly proportional_ to the number, then the number would _not_ have been the number demanded for the equable distribution. The second supposable objection is somewhat better entitled to an answer. It is an admitted principle in Dynamics that every body, on receiving an impulse, or disposition to move, will move onward in a straight line, in the direction imparted by the impelling force, until deflected, or stopped, by some other force. How then, it may be asked, is my first or external stratum of atoms to be understood as discontinuing their movement at the circumference of the imaginary glass sphere, when no second force, of more than an imaginary character, appears, to account for the discontinuance? I reply that the objection, in this case, actually does arise out of “an unwarranted assumption”—on the part of the objector—the assumption of a principle, in Dynamics, at an epoch when _no_ “principles,” in _anything_, exist:—I use the word “principle,” of course, in the objector’s understanding of the word.