Be this as it may, whenever we see a cause act, we look upon its effect as natural: when this cause becomes familiar to the sight, when we are accustomed to it, we think we understand it, and its effects surprise us no longer. Whenever any unusual effect is perceived, without our discovering the cause, the mind sets to work, becomes uneasy; this uneasiness increases in proportion to its extent: as soon as it is believed to threaten our preservation, we become completely agitated; we seek after the cause with an earnestness proportioned to our alarm; our perplexity augments in a ratio equivalent to the persuasion we are under: how essentially requisite it is, we should become acquainted with the cause that has affected us in so lively a manner. As it frequently happens that our senses can teach us nothing respecting this cause which so deeply interests us--which we seek with so much ardour, we have recourse to our imagination; this, disturbed with alarm, enervated by fear, becomes a suspicious, a fallacious guide: we create chimeras, fictitious causes, to whom we give the credit, to whom we ascribe the honour of those phenomena by which we have been so much alarmed. It is to this disposition of the human mind that must be attributed, as will be seen in the sequel, the religious errors of man, who, despairing of the capacity to trace the natural causes of those perplexing phenomena to which he was the witness, and sometimes the victim, created in his brain (heated with terror) imaginary causes, which have become to him a source of the most extravagant folly. In Nature, however, there can be only natural causes and effects; all motion excited in this Nature, follows constant and necessary laws: the natural operations, to the knowledge of which we are competent, of which we are in a capacity to judge, are of themselves sufficient to enable us to discover those which elude our sight; we can at least judge of them by analogy. If we study Nature with attention, the modes of action which she displays to our senses will teach us not to be disconcerted by those which she refuses to discover. Those causes which are the most remote from their effects, unquestionably act by intermediate causes; by the aid of these, we can frequently trace out the first. If in the chain of these causes we sometimes meet with obstacles that oppose themselves to our research, we ought to endeavour by patience and diligence to overcome them; when it so happens we cannot surmount the difficulties that occur, we still are never justified in concluding the chain to be broken, or that the cause which acts is SUPER-NATURAL. Let us, then, be content with an honest avowal, that Nature contains resources of which we are ignorant; but never let us substitute phantoms, fictions, or imaginary causes, senseless terms, for those causes which escape our research; because, by such means we only confirm ourselves in ignorance, impede our enquiries, and obstinately remain in error.