PREFACE.

that he once condescended to form an Hy-pothesis to shew that it might be done byImpulsion, and that of a very subtle ElasticSpirit or Æther. But as he was not able toprove the Existence of any such Thing, heseemed not at all delighted with the Thought,nor ever laid any Stress upon it; and accord-ingly we have not admitted it as a Principleof the Newtonian Philosophy. Besides, sup-pose this could be proved, we should stillbe at a loss to account for the material Causeof this very great Elastic Power between theParticles of this Æther; we should indeedadvance three or four Steps higher on theinfinite Ladder, but should be equally non-*plus'd with the mechanical Cause of Elajlicitythen, as we are at present with that of Gra-vity. But after all, ’tis evident by Experi-ments that this Power which actuates Bodies,whatever it be, is not either AttraSlive or'Repulsive solely; but it produces both thedifferent Effects in different Circumsances ofDi/lances. Thus the Loadstone at one Dis-tance moves the Needle towards itself atanother Distance it causes it to recede or movethe contrary Way. This Power in Iron isattractive, if touched upon the Stone in oneDirection; but if in a contrary it becomesrepulsive. The same ambiguous Propertiesof this Power obtain in Electriciiy-, and un-doubtedly