There is scarcely any thing to which an inquisitive mind, such as a philosopher possesses, submits with more reluctance, than to the inability of assigning the causes of the most interesting appearances or phenomena of nature. That every effect has a cause, is a first or self evident principle, and the mind is not easily brought to acquiesce in its utter ignorance of the cause, when the effect is visible and striking.—From this circumstance proceeded the numerous wild, fanciful, and delusive systems of natural philosophy, which existed before the time of the great Lord Bacon.—His penetrating and discriminating mind saw that nothing solid could ever be achieved in that noble science, unless such a procedure were relinquished;—unless men would consent to confess their ignorance of causes which were actually unknown;—unless they would cease to rely on hypotheses, however plausible, until they were verified by experiment;—consent to take facts as they are found, and by experiments alone endeavour to ascend to their causes. On this immoveable base the Newtonian philosophy is founded, and it will of course prove as durable as nature herself. Two things, however, in regard to this subject, are of some importance to be remarked.—The first is, that experiments may sometimes be supposed to ascertain causes which will afterwards be found not to exist, or to be wrongly assigned; because the experiments had not been accurately or extensively made. The second remark is, that though hypotheses are not to be taken for philosophy, till they have stood the test of experiment; yet in the process of the mind in making discoveries, hypothesis is perhaps always used, where the discovery is not merely accidental. No man can rationally make experiments till he has conceived a notion, supposition, or hypothesis in his mind, which he imagines experiment may serve to verify.—It is this which prompts him to his researches and guides him in conducting them. In regard to electricity, it is remarked by Dr. Priestley, that “no other part of the whole compass of philosophy affords so fine a scene for ingenious speculation. Here the imagination may have full play, in conceiving of the manner in which an invisible agent produces an almost infinite variety of visible effects. As the agent is invisible every philosopher is at liberty to make it whatever he pleases, and ascribe to it such properties and powers as are convenient for his purpose. And, indeed, if he can frame his theory so as really to suit all the facts, it has all the evidence of truth, that the nature of things can admit.”